1. CPU Board Repair.
To many, Gottlieb System80 CPU boards are regarded as a repair "challenge". This
notion exists largely because of the lack of a power-on LED test
system (as 1977-1985 Bally CPUs have).
With a Bally CPU board, the "seven flashes" pretty much tells the user
what is wrong on the board at power-on. Since Gottlieb's System80 does not have this
power-on LED test system, it is slightly more difficult to diagnose problems
(apparently Bally's convenient test system makes Gottlieb repair look "difficult").
But once the user knows the "systematic approach", most System80 CPU boards
can be diagnosed quickly and easily.
Assumptions.
The following relates to fixing just the CPU board on System80 and System80A
and System80B (there are some slight variances with sys80B). It assumes
the power supply is good, and is outputing +5, +8, 42 and 60 volts
(or that the CPU board is being tested on a work bench with an external +5 volt power supply).
Also it assumes the original Gottlieb power supply trim pot is adjusted so the
CPU board is getting 5.0 to 5.2 volts (the only voltage needed for
the CPU board is +5 volts; the other voltages are used for the score displays).
And finally that the big 6800 mfd capacitor in the bottom of the cabinet should
was replaced with a new 10,000 mfd cap (or higher, up to 15,000 mfd). If this cap
is the original, go and replace it now!
Also for testing purposes, all CPU board connectors should be
removed except A1J1 (+5 volt power and ground to the CPU board),
A1J2 and A1J3 (these two connectors go to the score displays, and
are on the right side of the CPU board). Connector A1J5 (slam and tilt,
test, credit and replay/start switches) may also be needed.
The rest of the CPU connectors should be removed (disconnected).
The last assumption is that the slam switch modification is made
to the CPU board. The normally closed slam switch is located
at the coin door of the game. If this switch is open (or the switch's
wires are cut/damaged, or the A1J5 connector is bad), the CPU board will
never boot. For those reasons, this modification should always be
performed. A picture of this modification is shown below.
If this modification is made, connector A1J5 should be
removed when testing the CPU board.
If the slam mod as outline at the link above is not done,
at minimum CPU connector A1J5 pin 10 must be grounded.
This does the same thing as the slam switch modification,
but in a non-permanent manner.
When working on any CPU board, this modification
should be made. Otherwise the CPU board will never
boot, unless CPU connector A1J5 is connected, and the
slam switch is closed. Alternatively A1J5 pin 10
can be shorted to ground.
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If the slam switch modification is not made, and the slam switch
is open (or connector A1J5 removed), the score displays will
"strobe" immediately at power-on. That is, when the System80 or System80A
CPU board is powered on, immediately (no five second delay!)
the displays will show zeros and strobe. On System80b CPU's,
a message will display saying the slam switch is open.
For later diagnostics, connector A1J6 (the switch matrix) can be
attached. This will enable the playfield switches.
Using an External Power Supply for CPU board Bench Testing.
If the entire game is not available, or it is just easier to
work on the CPU board on a work bench, an external power supply
can be used to power the CPU board. This won't test every
aspect of the system80, sys80a or sys80b CPU board, but
most things can be tested in this manner. Note the slam switch
should be performed for this testing method too.
If the slam mod as outline above is not dones,
at minimum CPU connector A1J5 pin 10 must be grounded.
This does the same thing as the slam switch modification,
but in a non-permanent manner.
On the left is a video game switching power supply.
On the right is a used computer power supply. Either
will work fine for a test power supply. Note the computer
power supply connector on top of the box is the one
that will supply our +5, GND and +12 volts. This plug
was used to power drives (hard drive, CD rom, etc).
Red is +5, black is GND, and yellow is +12.
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Using alligator clip leads, jump the +5 volts from the power supply (computer power
supply red wires) to the CPU board connector A1J1 pin 1 and/or pin 2
(the two pins on connector A1J1 closest to the bottom edge of the CPU board).
Then jump ground from the power supply (computer power supply black wires)
to the CPU board connector A1J1 pin 4 and/or pin 5
(the two ground on connector A1J1 closest to the top edge of the CPU board).
Now the external power supply is ready to be used with the system80 CPU board
(don't forget to do the slam switch mod).
A. Prelimary Work.
Battery Corrosion.
All Gottlieb System 80 boards use a recharagable "DataSentry" nicad 3.6 volt battery.
When these batteries don't get used regularly and get old, they can leak the
alkaline potassium hydroxide and volatile gases that destroy the
CPU board components and connectors.
Battery leakage causes more CPU board problems than anything else!
Remove the old battery from the CPU board immediately, and throw it away.
Until the battery corrosion on the CPU board is fixed, all bets are off!
It is really not even worth trying to fix a CPU board until the battery is
removed and all the battery corrosion is neutralized and removed.
Of course this means also replacing all the effected parts too.
The problem with battery corrosion is this: intermittent behavior! Some times
the board will work, some times it will not. This intermitten behavior is
almost always attributable to battery corrosion.
The Gottlieb DataSentry battery. This battery
has leaked only slightly (note the corrosion to the
crystal). This board was lucky. Also shown below the
battery are the Z3 (7404) and Z2 (7474) chips.
These are often affected by battery leakage.
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Battery Corrosion and the CPU Board's Reset/Clock Circuits.
Battery corrosion can do nasty things to the left side of the CPU board.
This is the "reset" section of the CPU board (and below the crystal Y1 is
the "clock" section). See
index1.htm Battery Corrosion1 section
for info on fixing this.
Fortunately
Great Plains Electronics (GPE)
sells a kit that includes all the parts needed to fix the reset section.
For less than $10, this kit is a bargain and makes fixing battery corrosion
in the reset area a lot easier.
Using a Dallas/Maxim DS1811 in the Reset Section.
There is also another way to fix the reset section with just a four parts (that
replaces nearly 25 parts!)
This involves using the new Dallas/Maxim Semiconductor D1811 reset chip (TO-92 package).
This inexpensive device looks like a transistor, but is really a three leg chip
in a TO-92 transistor package. See the
index1.htm Dallas section for more details.
Removing the Old Battery and Fixing Corrosion.
See the index1.htm Battery Corrosion2 repair
section for help with that.
The HOT Chip Feel Test.
Any TTL (74xx chip) that is hot to the touch should be suspected and tested. Sometimes
this is a quick and dirty way to find a problem chip. Note the 6532 RIOT chips at U4,U5,U6
do run quite warm. But the other 20 pin and less CPU chips should not be hot to the touch.
B. Testing the Reset Section.
Now that the battery corrosion is handled, we can actually start testing the
CPU board. When the CPU board is first powered-on, the Reset pin 40 on the U1 CPU chip
(6502) is held low. This allows the board voltages to come up smoothly to +5 volts.
After this, the Reset pin 40 should go high to about 4.5 volts.
With this in mind, the first thing to test is U1 pin 40. Using a DMM (Digital Multi-Meter)
put the red lead on pin 40 of U1, and black lead on ground. Turn the CPU power on, and
the DMM should go from 0 to about 4.5 volts DC, in about one second.
If anything else happens (like Reset staying
at zero, or only going to 2.5 volts), the reset section of the board is bad!
Of course the reset section was rebuilt in the above section, so pin 40 should go
to 4.5 volts, right?
The most common culprits in the reset section are transistors Q1 to Q4,
and the resistors (which can go open) and diodes
around these transistors. If the reset section was rebuilt in the
above steps, all these components should be new. So the only thing
left is the wrong part was installed, or a part was installed "backwards".
Occassionally the Z4 CMOS 4081 chip can die (which is
included in GPE's system80 reset kit), but this is rare.
Again the GPE reset kit is very useful here, as it contains all
the parts needed to fix the reset section.
Also check for a broken trace (common, especially on boards with battery corrosion).
For example, the ground trace goes around the negative battery solder pad before
going to the areas at the bottom left of the board (the clock circuit).
Often battery corrosion can cause a loss of continuity to this area.
Often I will scrape the whole reset section of the CPU board and go
with the Dallas DS1811 reset transistor.
This will fix the reset section with just a four parts (that
replaces nearly 25 parts, which can be removed).
The advantage to the Dallas DS1811 is great: if a system80 CPU board
has had some battery corrosion and perhaps some circuit board traces
are questionable, the new Dallas part will not utilize most of that.
So even a board with lots of corrosion can have 25 reset parts cut out,
and just the Dallas installed. So most of the questionable traces
on the component side of the circuit board are eliminated too, making
battery corrosion less of an issue.
Here are the installation steps for this Dallas DS1811 chip:
- Remove reset parts: chip Z1, trans Q1-Q4, diodes CR33, CR35, VR1, resistors R8, R9, R43-R50,
caps C2, C25, C36.
- Install a jumper from Z1 pin 5 to Z1 pin 9.
- Install a jumper from Z1 pin 11 to Z1 pin 13.
Be careful not to accidentally connect pin 12 to the jumper,
as it will cause the reset modification to not work.
- Install a jumper where R45 was installed.
- Install a jumper between the two top holes of Q3 (the Emitter and Base).
- Install the Dallas DS1811 (TO-92 package) into the top pads of R50, R44, R49 (pin 1=R50, pin 2=R44, pin 3=R49).
Note the flat edge of the DS1811 faces downward away from Z1, toward the dip switches.
- Retain reset parts CR34, R7 and C3.
- Note R10 and C14 can be remove or left installed.
Since Z1 has been removed, R10 and C14 are no longer used, and can be
removed (or left installed).
Picture of the Dallas DS1811 installed in the Sys80 CPU board.
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After the reset is tested successfully at the CPU chip pin 40, repeat the test
on the RIOT chips U4,U5,U6 pin 34. If the reset
is not behaving as on the CPU chip (going low for just a moment, and
then staying high), look for a broken trace. The reset signal on the CPU
chip pin 40 should have continuity with all the RIOT chips' reset pin 34.
C. Testing the Clock Circuit.
After the Reset section is tested and working, and the board still does not work,
next test the Clock circuit. The clock is required for CPU timing, and
is handled by the Y1 crystal, chips Z2/Z3, and resistors R3-R5. If the reset section
was rebuilt with GPE's kit, a new crystal, chips Z2,Z3 and the
resistors should have been installed (yet another reason for GPE's kit).
The Radio Shack logic probe showing the Clock signal on the CPU chip U1 pin 37.
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Here are the steps for testing the clock section:
- Get a logic probe and connect it to power.
A DMM can be alternatively used, but really a logic probe is better.
- Put the logic probe on U1 pin 37. This is the CPU's clock signal
(also known as "phase 1 clock").
- Turn the power to the CPU on. About one second after power is applied,
the clock signal should appear. It should be a pulse
signal. If using a DMM, about 2 volts DC should be seen (but again, a logic probe should be
used). If this signal is missing, there is a
problem in the clock circuit at chips Z3/Z2 which supplies the CPU. Skip to the next section.
- Next put the logic probe on U1 pin 39. This is the "shifted" clock
signal (also known as "phase 2 clock") from the CPU (if both pin 37 and pin 39 were
put on an oscilloscope, the time shift can be seen between the two signals).
If no phase 2 clock signal at pin 39, the CPU chip U1 (6502) is bad.
- Put the logic probe on Z3 input pin 11. The same shifted clock signal as
seen in the previous step. Then check Z3 output pin 10, which then feeds
to Z3 input pin 13. Finally the check Z3 output pin 12 (which feeds the shifted clock
to the rest of the CPU board). If any output signals at Z3 are missing, this chip is bad.
- Check the shifted clock signal at the RIOT chips U4, U5, U6. The shifted clock should
be present on these chips at pin 39. If the signal is missing, there is probably
a broken trace.
The Radio Shack logic probe showing the Clock signal on Z3 pin 1
(looks about the same for the leads of the crystal, chip Z3 pins 2-6,
and Z2 pins 3,11).
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If Pin 37 of U1 has no pulsing clock signal, try these tests:
- Put the logic probe on either lead of the crystal Y1. A tight pulsing
clock signal should be seen. Check both leads of the crystal. No signal,
replace the crystal and/or check resistors R3,R4,R5.
- If there is still no clock signal at either/both legs of the crystal
(and the crystal/resistors R3-R5 are good), try this: connect a 10pf or 20pf capacitor from
each leg of the crystal to ground. If it solves the problem, leave the capacitors
installed. If it does not, remove the capacitors.
- Make sure chip Z3 is a 7404, and not a 74LS04 or 74S04 or 74HCT04.
- Check chip Z3 pins 1,2,3,4,5,6. If the clock is missing on any of those
pins, Z3 is bad.
- Check chip Z2 pins 3,11. The same clock signal as the previous
step should be seen, as this is the clock input from chip Z3 to Z2.
- Check chip Z2 pins 2,5,8,9,12. A more square clock signal should be seen.
If missing, chip Z2 is bad. Note chip Z2 pin 9 goes directly to the CPU U1 pin 37.
The Radio Shack logic probe showing the Clock signal on Z2 pin 12 (looks about the
same for Z2 pin 2,5,8,9, and CPU U1 pin 37).
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D. Test the RDY and IRQ.
Now that the Reset and Clock are tested and working, it is time to test
the RDY and IRQ signals.
The RDY (Ready) is easy to test. Put a DMM set to DC volts on CPU chip U1
pin 2. Power-on the CPU board. The DMM should show +5 volts,
and stay at +5 volts. There is not much to fix here. RDY is connect directly
to +5 volts through a 4.7k ohm resistor at R2.
Next test the IRQ signal. For system80, put a DMM set to DC volts on CPU chip U1 pin 4.
Power-on the CPU board. The DMM should show +5 volts DC (IRQ high) for the initial five seconds,
and then change to about 3 volts (pulse) when the score displays turn on (and the CPU board is
fully initialized). If using a logic probe, again the IRQ will be high for the
first five seconds, and then pulse when the displays come on.
On system80A and 80b, the IRQ should go straight to about 3 volts DC upon
power-on. There is no 5 second delay, as there is with the earlier
System 80 CPUs.
If the IRQ is low, then chances are one of the 6532 RIOT chips is damaged. The most likely
RIOT culprit is U4 (switch matrix), or one of the TTL chips that feeds it (Z11, Z12,
Z13, Z14, Z15). Also note IRQ is connected to +5 volts through resistor R1 (3k ohms);
verify that resistor is not damaged. If the IRQ is stuck high and never starts to
pulse, this can often mean the U2/U3 game rule ROMs are damaged.
E. Test the Address/Data Lines.
If the CPU board is still not booting, the next step is to check the address and data lines.
Each of the following chips have the address and data lines: U1 (CPU), U2/U3
(2332 game rule ROMs), U4/U5/U6 (RIOT chips), and PROM1 (the 2716 EPROM).
Also the address lines and some data lines will be at chip
Z5 (the 5101 RAM chip).
There are twelve address lines, labeled A0 to A11. And
there are eight data lines, labeled D0 to D7. The above chips' address and data
lines are all tied together. Therefore if the A0 address line is pulsing at the
U1 CPU, it should also be pulsing on U2/U3, U4/U5/U6, and PROM1. If it is missing
on one of these chips, that means there is a broken circuit board trace.
Test for address and data lines is done with a logic probe. Start with address
line A0, and have the probe on that pin of the chip to test. Turn the CPU board
power on, and watch the logic probe. The CPU board often can not just be left on.
Sometimes an address or data line will start to pulse,
and then stop. This often happens if the U2/U3 ROMs or PROM1 (game EPROM) is bad.
So powering the CPU board off and on between address/data line tests may be required.
What if *none* of the address or data lines are pulsing? (That is, they are either
high or low.) This usually means the program in the ROM chips at U2/U3 and PROM1
could not be selected and read (hence the program is not running). The ROMs chips
at U2,U3 or PROM1 could be bad, or the chips that select the ROMs (Z7, Z10, Z12)
could be bad. Finally Z1 in the "up/down memory protect logic" circuit
could be bad too.
F. The RIOT Chips.
Chip U4, U5 and U6 are 6532 RIOT chips. These are large 40 pin chips, and often they fail.
If any one of the RIOT chips fails, that can lock up the CPU board. RIOT U4 handles
the switch matrix. This chip is particularly troublesome. If any of RIOT U4's input
TTL chips at Z11, Z12 (switch strobes/row) and Z13, Z14, Z15 (switch returns/columns)
fail, this can lock the CPU board. For example, if Z12 is missing or failed, the CPU
board will not boot. Also if chip Z14 is missing or failed, the CPU board comes up
immediately with "000000" in the displays (like the slam switch is open). Chips
Z11, Z13 can be missing and the CPU board will still boot.
Switch matrix chips Z13, Z14 (returns/columns) input pins 1,2,4,5,9,10,12,13
can be viewed with a
logic probe. They should be strobing, as they are the switch returns, and
connect directly to the playfield switches. None of these should
be stuck low! If one is stuck low, the CPU board may not boot (by forcing the IRQ low).
Then test the Z13, Z14 output pins 3,6,8,11. If these outputs are all strobing,
but an input is not, replace the chip (7400). If neither the input or outputs
are strobing, then the U4 RIOT
chip is probably bad. Also note that Z15, the switch enable chip, could be causing
problems here too (and this also uses one gate from Z12, pins 12/13).
The switch matrix strobes/rows should also be tested. This is mostly chip Z11, with two
gates on Z12 also used. Check Z11's input pins 2,4,6,8,10,12 (these go directly to the
playfield switches). Then check Z11's output pins 1,3,5,9,11,13. Also Z12's input
pins 2,4 and output pins 1,3 should be checked.
RIOT U5 (score display control) and RIOT U6 (lamp and solenoid control) are slightly
less troublesome. But they can still cause problems. A bad U5 score display RIOT can
lock on the CPU board and destroy a score display.
Also test the CS1 and CS2 lines on the RIOT chips U4,U5,U6, pin 38 (CS1) and pin 37 (CS2). If
CS1 (pin 38) is not pulsing, chips Z7 and Z8 handle this (the schematic has an "input/output
device selection").
G. Chips Needed (or Not Needed!) for CPU to Boot.
Chip Z5 (5101 RAM) can be removed, and the
System80 board will still boot. Sometimes a bad 5101 will stop the CPU board from
booting, so temporary removal can help diagnose this.
Unfortunately, all the RIOT chips (U4,U5,U6) must
be installed for the CPU board to boot.
Fortunately,
Leon Borre has developed a test program
for the RIOT chips. The procedure for this testing follows.
Also GPE has a test board, and there is a NOP test that
can be run.
The GPE Test Board QuickScan80 (QS80).
Great Plains Electronics has a very nice test board for
System80 CPUs, and is selling it for about $55. It basically encorporates
the ideas of the Leon test EPROM (including the LED flashing) in a simple "plug and play"
board via the empty 40 pin socket across the top of any system80 CPU board.
If you don't want to do any soldering or EPROM chip programming,
this may be a good alternative. The board is available from
Great Plains Electronics
(www.greatplainselectronics.com) and is called thier QuickScan80.
I highly recommend this product for those not interested in making
a similar item themselves.
Connecting the QS80.
Make sure the QS80 has its DIP switch set correctly:
For system80 or sys80A use these settings:
- DIP1=off
- DIP1=off
- DIP1=off
- DIP1=on
For a sys80B uses these settings:
- DIP1=on
- DIP1=off
- DIP1=off
- DIP1=off
The unboard jumper on the QS80 is used to control the watchdog timer.
This should be disabled and set to the OFF position.
Connect the ribbon cable connector to the empty TC1 socket at the top
edge of the system80 CPU board.
The QS80 has a "CP2" jumper wire that is necessary for the QS80 to work.
This jumper disables the U2/U3 ROMs on the system80 and sys80A CPU boards,
so the board will use the ROM space on the QS80. Connect the jumper
to the top side of resistor R42 (this resistor is in the upper left corner of the CPU board
near the main power connector and near chips Z9, Z10). On sys80B CPU boards the jumper is not
needed, but the 2764 u2/u3 EPROM must be removed from the CPU board.
Make sure you have a good +5 volts going to the CPU board.
Never connect/disconnect the QS80 with the power on. Never change
any DIP settings, jumpers or connectors with the power on.
Important! If you connect the Quickscan board "one pin off" on the
40 pin ribbon cable, you will blow up the PAL chip on the GPE board!
Running the QS80.
Before the QS80 will work, the CPU board must have good Reset and Clock
signals. This is easy to identify as the QS80 has two LEDs - if either Clock or Reset
LEDs are red, the QS80 won't work. IF the IRQ LED is red there is no IRQ activity
(green means IRQ is active, meaning the ROM firmware is running).
If Reset and Clock are good, the self test will begin. Here are the tests,
THOUGH YOU WILL NOT SEE THESE TESTS, the are indeed happening (unless
otherwise noted):
- Test 1: Make sure U4 is alive and responsive.
- Test 2: Make sure U5 is alive and responsive.
- Test 3: Make sure U6 is alive and responsive.
- Test 4: Interupt test. Disable all RIOT interupts and turn on CPU interupt enable.
If this test fails the QS80 reports a "0" "F" (IRQ Error).
- Test 5: U4 hex 55 memory test.
- Test 6: U4 hex AA5 memory test.
- Test 7: U4 random memory test.
- Test 8: U4 port B I/O test.
- Test 9: U4 timer test.
- Test 10: U5 hex 55 memory test.
- Test 11: U5 hex AA5 memory test.
- Test 12: U5 random memory test.
- Test 13: U5 port A I/O test.
- Test 14: U5 port B I/O test.
- Test 15: U5 timer test.
- Test 16: U6 hex 55 memory test.
- Test 17: U6 hex AA5 memory test.
- Test 18: U6 random memory test.
- Test 19: U6 port A I/O test.
- Test 20: U6 port B I/O test.
- Test 21: U6 timer test.
- Test 22: Z5 5101 RAM hex 5 test.
- Test 23: Z5 5101 RAM hex A test.
- Test 24: Z5 5101 RAM random test.
After completion of the Z5 5101 test the RAM memory is clear
(high scores, configurations, credits, etc).
If any of the above tests fail, the following number is reported on
the numeric LED display along with a "F" (for fail):
- 4 = U4 6532 RIOT bad. "4" and "F" will flash repeatedly if bad.
- 5 = U5 6532 RIOT bad. "5" and "F" will flash repeatedly if bad.
- 6 = U6 6532 RIOT bad. "6" and "F" will flash repeatedly if bad.
- 1 = Z5 RAM 5101 bad. "1" and "F" will flash repeatedly if bad.
Important! If you get an error that U4 and another PIA have "F"ailed,
replace the higher order PIA chip FIRST. For example on a System80b board I was
testing, the U5 and U4 chips both showed "F"ailed. But in reality, only
the U5 chip was bad. Because how U4 chip is tested, sometimes the QS will
report U4 as "F"ailed, because U5 or U6 is tainting the Quickscan test results for U4.
If the clock, IRQ and reset are good and the QuickScan can boot properly,
the Quickscan80 will test the U4/U5/U6 RIOT chips and the Z5 5101 RAM.
A good way to use the QuickScan80 is to pull all three RIOT chips and the 5101 RAM and
boot the CPU with the QuickScan80 installed.
The QuickScan80 should sit in a continuous loop saying all three RIOTs and 5101 are
bad (via it's numeric LED display),
and should never jump out of this test mode. If this does not happen, there's a good
chance the QuickScan80 is not running correctly, perhaps because of a broken
address or data line trace on the board or a bad 6502 chip. But if the QuickScan80 is stuck saying all
three RIOTs and the 5101 are bad, power off and then
replace each pulled chip back into its socket one at a time,
and re-boot with the QuickScan80.
As the chips are replaced, the QuickScan80 test should not report the replaced
chip as bad. If it does, obviously that chip has a problem.
Start with the RIOT U4, then U5, then U6, and finally end by replacing the Z5 5101 RAM last.
If the QuickScan80 no longer reports any of the RIOTs or 5101 as bad, the system80 CPU
board is probably in pretty good shape.
There are some other QuickScan80 tests that
can be run after ther RIOT chips and 5101 RAM are tested. These tests are
run using the start button. This includes
Continuous retest (good for burn-in testing),
Lamp testing, Solenoid testing, Sound testing, Switch testing, and
Score display testing (For System 80 and 80A only).
After completely testing the MPU board, the QuickScan80 allows the user to
enter one of several modes:
- 1 -- Continuous retest (good for burn-in testing)
- 2 -- Lamp testing
- 3 -- Solenoid testing
- 4 -- Sound testing
- 5 -- Switch testing
- 6 -- Score display testing (For System 80 and 80A only)
The Leon Gottlieb Test EPROM.
This information was originally developed from Leon's web page.
The following instructions are my version of this web page (Leon is French,
so his version is a French-to-English translation). To use this
procedure, a 2732 (or 2764) test EPROM will need to be downloaded, burned
and plugged into the system80 CPU board at chip location U3.
Unfortunately, system80 and system80a CPU boards are not able to
use an EPROM directly at this location.
To modify a CPU board for a single 2764 EPROM to replace the U2/U3 masked 9332
ROMs, see the system80 repair guide part two here.
System80 games do not have a socket at U2/U3, so
sockets need to be added and the CPU board modified to accept an EPROMs at
U2/U3 (the stock ROMs are 9332 masked ROMs). The large 40 pin TC1 socket across the
top of the CPU board can also be used, but that involves a bit of
tricky wiring. Details of using TC1 are at the link above on Leon's web page.
EPROM Test File Images.
The Leon system80 Test EPROM test files can be downloaded by clicking
here.
This file is in ZIP format.
Introduction.
The basic idea was to create the same test-program for
Gottlieb System80 as was done for the other pinball CPUs including Bally and
Williams. That is, an output test on the RIOT chips so these ICs could
be tested, and included a way to deal with
the other basic elements, such as the CPU and select lines needed
to start up the CPU-board. I made such a
program but than came the question from the marvin3m.com site
to add a visual control to this test. Because Gottlieb has no
LED indicator or display to give any hint when the CPU is
booting on your work-bench. As that was a very good idea I
added the LED, and finished the whole thing that way. We
tested the program and everything was OK, but as the whole
thing was looking more and more like the 1977-1985 Bally CPU self test.
Hence marvin3m.com suggested to make a Bally-like test program with the classic
"LED flashes". An easy question but not an easy thing to
do. As I already put a lot of time in this project, why not
make a 100% job of it? So again I did some testing
and found out how to do the "flash" test and how to
avoid the inconveniences of the Bally test, because the Bally
test has some weak points (for example, on the Bally CPU,
the test LED is connected to PIA
U10, and when one PIA output is dragged down or failed,
the whole test may not work as the
outputs of the PIAs are not really tested).
The big advantage though to the Bally CPU is that the CPU and PIA chips are
socketed, where on Gottlieb's CPUs this is not normally the case. So
there's one more reason to have a good diagnosis before unsoldering a lot
of parts on a Gottlieb CPU board.
A company has also made a similar device to this System80 test ROM,
and is selling it for about $55. It basically encorporates
the ideas of this test EPROM (including the LED flashing) in a simple "plug and play"
board. If you don't want to do any soldering or EPROM chip programming,
this may be a good alternative. The board is available from
Great Plains Electronics
(www.greatplainselectronics.com) and is called thier QuickScan80.
I highly recommend this product for those not interested in make
one themselves. Also below there are instructions for an alternative
to a test EPROM (the NOP Generator). This is an useful alterative too.
Fitting the Test EPROM:
The test is in an EPROM, which can be
fitted to the Gottlieb board in different ways. Because the
Gottlieb SYS80 come with 3 different CPU boards: SYS80, SYS80A
and SYS80B. I have an "universal" solution, with more preliminary
work and soldering (but will easily adapt to any of the three
System80 CPU board types), and a "simple" solution which can be
impliemented for those who repair only an occasional System80 pinball or
perhaps are confronted only with only SYS80A or SYS80B boards (because
the original SYS80 CPU board does not have chip U3 socketed, which is needed
to implement the "simple" solution). But the choice is yours which method
to use.
The Tests:
The test works as follows. The test EPROM
controls the 6502 CPU, then the 5101 RAM, and then the select lines
of the three RIOT chips (remember the RIOT chips are the I/O chips which
interface the 6502 CPU to the game's peripheral coils, switches and lamps).
If each of the components tests good,
a flash is seen on a connected LED for each device (except for the
inital test of the 6502 CPU). After
the first four LED flashes, the test goes on and will continuously test the outputs
of the three RIOT chips by pulsing them between 5 volts and 0 volts, on and off.
This last part of the test is non-blocking; this means that when
one or more RIOT outputs are dead, the test continues to run.
It's up to you to measure the outputs of the RIOTs
to see if they "dance" (pulse/move) between 5 and 0 volts (a logic probe works
best for this, but a DMM can often be used). But keep in mind when the
initial tests find a CPU/RAM/RIOT select fault at power-on,
it will continue the failed test on
the bad component, until the fault is repaired (much like the stock
1977-1985 Bally boot-up test). Then after the first four flashes (tests),
the test program will continue checking the RIOT outputs.
This means that only a failed RIOT output would be broken if the test
gets to the continual LED flashing faze
(as the 6502 CPU, 5101 RAM, and the select lines of the three RIOT
chips have already been tested). This works better than the
Bally test EPROM, because it avoids using an
indicator LED connected directly to the address A6 line.
The tests are contained in its own EPROM, and are not depended of the game
ROMs or PROMs. The outputs of the RIOTs are controlled in the
second part of the test, and I added a special trick which allows
you to skip the initial 5101 RAM test. This is convenient because the 5101 RAM
often fails, and are expensive/hard to find. Note the
Gottlieb system80 CPU does not require the 5101 RAM to be present to boot
(it only saves the game's audits and high scores).
So if you would like to keep working on the CPU board after a one flash
diagnosis (a failed 5101 RAM), and continue and test the RIOT chips,
it can be easily done.
Important Note:
When applying the 5 volts to the board there is always
a automatic reset, which puts the internal CPU and RIOT registers in
their start (reset) position.
During this brief moment the state of the address bus
A6 is not stable and the control LED connected to it can
flash. This is an uncontrolled "flash", and can mix-up
our LED flash counting. To avoid this, the test program gives the first
MEANINGFUL "flash" only after about 5 seconds (which we
should all be used to on Gottlieb CPUs because all System80 {not 80a/80b} CPU
boards have a five second boot-up delay anyway). So if
you see a LED flash immediately after power-up, do not
count that one!! At power-up count to yourself "1,2,3,4,5", and then start
counting the meaningful LED flashes. Be sure the uncontrolled
power-on flash (if present) is not counted.
A "flash" means the LED lights up and then
turns off, and is counted as a sucessful "flash".
If the LED lights up and stay on, this is NOT counted
as a "good flash".
After several days of corresponding with
Marvin3m.com, I came up with an universal solution which works fine
with ALL system80 CPU boards (SYS80, SYS80A, SYS80B).
There is a more simple solution, but the Test EPROM
works a little different for the three board types, and
you have to put a socket at CPU board location U3 on the SYS80
CPU board (this essentially allows the SYS80 CPU board to be treated
as a SYS80A board). Lets take a look at both solutions.
Simple version:
Here we use a free logic port on one unused CPU board TTL chip
to invert and combine the two selection signals BAB12
and BAB13. We also make a provision for a
"easy to come-by" A11 signal. After this modification
the three signals are always available for our test EPROM.
We must combine and invert the two BAB12 and BAB13 signals
on a SYS80 board because the board expects a ROM and not
an EPROM at board location U3 (which have slightly different
pin-outs). Hence
there are three signals that are slightly modified and
used on the U3 chip at pins 18,20,21.
Here you see the three wires, and these can stay on the
CPU board forever.
- Now Insert the modified socket in the CPU board socket at U3.
- Burn the Test EPROM code into a blank 2732 EPROM.
- Put the Test EPROM in the modified socket.
- On the parts side of the board, hook the yellow grip-pin to the "little star".
- On the parts side of the board, hook the blue grip-pin to Z9 pin 8.
Here you see the completed and working installation on
a SYS80A CPU board. To do this on a SYS80 you have to place
a socket at U3.
A test mounted simple version sys80 (a socket at U3 is
necessary) or SYS80A board, with the LED connected via red and
green grips, and the adapter inserted in U3 and connected with the
yellow and blue grip. In the middle of the board you see a little
red temporally jumper necessary to test the outputs of the U4 RIOT
(more on that later).
The test EPROM mounted on a SYS80B board. Plug in the Test EPROM
(2764) into the piggy board, and connect the LED.
The Universal Solution:
For those who want to use the test EPROM without changing
anything on the CPU boards or installing a socket at U3.
Also the test EPROM implemented
in this style can be used on ALL the system80 CPU board types,
as we use the empty TC1 connector present on ALL system80 cpu types.
Unfortunately some soldering work is required. But once done,
it can be re-used on other system80 CPU boards. But because of
the amount of work involved, and a similar version is available
for $55 from Great Plains Electronics, I don't really suggest
using this version of the test EPROM. In addition, there is an
alternative version (the NOP Generator) available which does
not even need an EPROM (see below). But the instructions are listed
here for those so inclined to go this route.
Parts Needed:
- (1) Perforated circuit board
- (1) LED
- (1) 1.2k ohms resistor
- (1) 47 nF capacitor
- (2) strip pins, 20 pins each (do not use wire wrap or large header
pins, as these will destroy the mating socket at TC1 on the CPU board).
- (1) 24 pin chip socket
- (1) 14 pin chip socket
- (1) 7404 IC chip
All pieces mounted on the board.
The two 2x20 pins strips are mounted on the component
side of the board, when the board will be fitted on the cpu it
will be reversed. Before you start soldering it is a good idea to
mark on the corners of the connector and sockets with their respective pin numbers,
as it helps counting for the right pin while soldering.
Here are the 32 connections required, and a few hours of
soldering! You can see the pin numbers on the corners of the TC1
connector.
This is the interconnections of the two ICs (2732 and
7404), and the LED.
Now connect the TC1 pins to the 2732 as stated in the list below:
| TC1 |
to |
2732 |
| pin 1 |
to |
pin 17 |
| pin 2 |
to |
pin 16 |
| pin 3 |
to |
pin 9 |
| pin 4 |
to |
pin 10 |
| pin 5 |
to |
pin 11 |
| pin 6 |
to |
pin 12 |
| pin 7 |
to |
pin 24 |
| pin 8 |
to |
pin 15 |
| pin 9 |
to |
pin 14 |
| pin 10 |
to |
pin 13 |
| pin 25 |
to |
pin 21 |
| pin 26 |
to |
pin 19 |
| pin 27 |
to |
pin 22 |
| pin 28 |
to |
pin 23 |
| pin 29 |
to |
pin 1 |
| pin 30 |
to |
pin 2 |
| pin 31 |
to |
pin 3 |
| pin 36 |
to |
pin 8 |
| pin 37 |
to |
pin 7 |
| pin 38 |
to |
pin 6 |
| pin 39 |
to |
pin 5 |
| pin 40 |
to |
pin 4 |
| pin 32 |
to 7404 |
pin 9 |
| pin 33 |
to 7404 |
pin 11 |
This tool will require a few hours of work. But once finished you have a
very good repair tools that will always serve you!
The test-board fixed on the cpu and working, the led is pointed
"upwards" to see it better. While testing, U2 and PROM1 can stay
mounted on the board.
Manual:
Simple solution:
- For a SYS80A (or a SYS80 with socket at U3),
place the test EPROM in the CPU socket at U3.
- For a SYS80B CPU board place the 2764 test-eprom in the piggy board socket.
- Connect the control LED's red grip on +5 volt and
the green on pin 15 of U1.
- Connect 5 volt to CPU board connector J1 pin 1.
- Connect Ground to CPU board connector J1 pin 5.
Universal solution:
- Place the test-board on the TC1 connector
- Remove U3 in case of a SYS80A.
On a SYS80B CPU board remove the game eprom (2764 on the daughter board).
In case of a SYS80 with a soldered U3,
you have to make one temporally connection in order to eliminate the selection of
on-board U2 and U3 ROM. Ground signal BAB13 temporally by connecting Z10 pin 6
to pin 7.
- Connect 5 volt to CPU board connector J1 pin 1.
- Connect Ground to CPU board connector J1 pin 5.
Although this is an SYS80A board, I mounted the universal solution
it like a SYS80 (as an example) with all
chips are still on the board (U3,U2,PROM1: the
selection of the on-board program chips is eliminated by the Z10 pin 6 to
pin 7 connection in the left upper corner). The second little red
wire you see in the middle is a temporally connection to test
outputs of the U4 (RIOT, as explained above). This test was
performed when I had the replacement RIOT for U4, while was
dead when I received this board. I used this dead RIOT to do my research and
testing, that is why on the other photographs the U4 socket is
empty.
Start:
When you power-on the 5 volts, count to five and then start
counting the LED flashes. Remember to ignore any immediate power-on flash
(which may or may not be present).
NO Flashes.
We start with the worst case of NO flashes.
The lack of any flash means there is a problem with
either the reset or clock circuits, or the CPU chip itself.
I assume you have reviewed the document at
www.marvin3m.com/sys80/index3.htm
and addressed any problems with the reset and clock circuits.
That only leaves the U1 6502 CPU processsor chip.
Simple solution: On SYS80A remove all ROMs, PROM1 and the Test EPROM. On
SYS80B remove the test EPROM and do not replace the game EPROM.
Universal solution: Remove the test-board from TC1. On SYS80 temporarily
connection must stay on Z10. On SYS80A remove U3 and U2. On
SYS80B leave the game EPROM out, and remove the PROM1 too.
As always we will look first at the processor and the selection
circuitry. Again as for the other repair methods, we work
without any program present. That way we force the cpu to pass
through all its addresses in a very fast manner. We look at the basic
signals the CPU chip needs to run.
First Check the CPU chip U1 itself. Check the following:
- pin 8 for +5 volts (main +5 volt feed)
- pin 1 for Ground (main ground feed)
- pin 40 for about +4 volts (reset pin)
- pin 4 for +5 volts (pull up from +5 volts)
- pin 2 for +5 volts (pull up from +5 volts)
- pin 37 for about +2 volts (clock signal)
- pin 34 for about +2 volts (R/W signal)
If something is missing, take out the schematic and follow the missing voltage back
to its origin. Both signals on pin 2/4 are only a pull-up
resistor tied to +5 volts.
Reset on pin 40 is the reset circuit which uses only two
chips. Pin 37 brings the clock-signal, again two chips.
Pin 34 is the R/W signal, and if missing the CPU chip itself
is bad or the signal is shorted. Bend or cut CPU U1 pin 34 from the
board, and recheck it. When pin 34 is free and there is still no signal,
the CPU chip is dead. When pin 34 is free and there is a signal,
there is a short somewhere on the CPU board pulling pin 34 down.
When these basic signals are
present, it's time to look at the address and data bus signals.
They must all be present, and between 0.5 and 3 volts. When
measuring them with the DMM voltmeter, the load on the
signals sometimes causes the processor to a halt (it is better
to use a logic probe to check for signals). So if one signal is
missing, switch the CPU board on and off and check again or look at another
good signal and then return to the missing
signal. If it will not "dance" the processor is broken or the
signal is shorted. As always release (cut or bend) the pin of the missing
signal. If the pin is free yet the signal is still missing,
it's for sure a bad CPU chip.
If the signal is present when the pin is bent/cut,
look for a short on the board in the manner described above.
The Selection of U3:
The program may not work because the processor does not
find the program chip. In the simple solution there is only one
signal to select the program chip at U3. The signal coming at
U3 pins 18/20 must be about 1 volt. The rest of the
selection is by the other address signals and these are already
controlled on the processor and chip Z7. In
case of the universal solution the selection signal is formed on
the test board itself so no control is needed (I need to verify this).
With a SYS80B simple solution control of the selection of the
2764 should show pin 21 at 3 volts, pin 23 at 4 volts, and pin 24 at 1 volt.
On the 7404 mounted on the piggy board measure pin 1 at 4 volts and
pin 2 at 0 volts. If not OK these signals are easy to follow with
the schematic.
One Flash:
The processor is OK but the 5101 RAM at Z5 is suspect. To skip this
test after the first flash, momentarily ground, for just a brief
moment, U1 pin 6. This causes an interrupt and the program
jumps directly to the RIOT test. As there is no reset involved
the flashing LED will occur immediately (assuming the RIOT is OK)
and you can continue your testing until Z5 is fixed.
In most cases it will be the RAM itself. But to be 100% sure we
will control the selection signals of this RAM. Restart the test
and after the first flash the program will continuously test the
RAM, and we measure the selection signals:
- Z5 pin 20 = 3.5 volts
- Z5 pin 19 = 3.5 volts
- Z5 pin 17 = 0.2 volts
- Z5 pin 18 = 0.2 volts
Also look at the data signals at Z5 pin 9 to pin 16, which should
be around 0.2 volts. Are these signals OK? If not replace the RAM.
Two flashes:
The second flash tests the U4 RIOT chip selection signal.
Three flashes:
The second flash tests the U6 RIOT chip selection signal.
Four flashes:
The second flash tests the U5 RIOT chip selection signal.
Selection Signal of the RIOT chips U4, U5, U6.
If the test is failing at flash 2,3 or 4, there is a RIOT chip
selection signal problem.
The RIOT chip selection signal is SEL2 (pin 37), which should
show 3.5 volts. Follow this to chips Z7 or Z9 or sometimes Z8
pin 38 (see schematic). To be completely sure look at the RIOT chips' pin
34 (Reset) and make sure it is +5 volt and pin 39 is +4 volt.
As there are only a few signals that look
at the RIOT chip selection signals, examine all three RIOT chips and
if again these signals are Ok, replace the RIOT chip in question.
Continuous flashing:
This means that all the initial tests passed, and the test program is
controlling the outputs of the RIOT chips.
With the voltmeter controls the outputs of all the RIOTS, they must
pulse from 0 to 5 volts. These chips include U4,U5,U6 pins
8-19 and 21-24. A few
pins may *not* move between 0 and 5 volts, as they are connected as inputs.
For example, U5 pin 15 will only move if connector
J5 pin 10 is shorted to ground. Other RIOT pins which do not move
are U4 pins 8-15. To test these outputs there are two things you
must do. First set the CPU board DIP switches 1-8
to ON. Second, temporarily connect Z15 pin 3 and 7 together. This
will make RIOT U4 pins 8 to 15 "dance" between 2 and 4 volts.
Now that every output has been controlled, it is easy
to see if any RIOT pins 8-19 and 21-24 do
not "dance" (using a Logic probe, or even a DMM).
If one pin is "dead", there is a trick that can be used
to see if it is the RIOT chip itself, or a short on the
board that is disabling this pin. For example, say RIOT U6
pin 10 is not pulsing. Temporarily shorted pin 10 to pin 9
using an aligator clip. This will cause one of two things to happen:
if both pins move than the RIOT is certainly dead at
the output (pin 10 in this example), and the entire RIOT should
be replaced. But if both pins no longer move, than there is probably a
short somewhere on the first output line (pin 10 in this example)
somewhere on the CPU board.
To verify the short, free this RIOT output (again pin 10 in this example)
by bending the RIOT pin out of its socket or cleanly cut the
RIOT's pin 10 (if the chip is soldered to the board).
If the RIOT output pin still does not move when freed, the RIOT chip has failed.
If the RIOT output moves when freed, than there is a short on the board
connecting to this RIOT output line. Follow the line using the schematics
and check those connecting components.
Eliminate a component by temporarily cutting the suspect shorted component.
If all connecting components have been checked and temporarily removed
from the circuit, and the RIOT output still does not move,
the RIOT chip itself may still be the cause.
Other Test EPROM tips.
When you decide to use this test program, I think it's a good idea
to use it first on a good working CPU board. This will allow you
to check all the RIOT outputs to verify your procedures.
The test EPROM can simulate problems on a working CPU board by
bending up a leg of the RAM or RIOT chip you choose.
Bend up a data line arrival or a selection pin.
If the chips are soldered you can ground
a selection pin (but not a data pin because the test will never start
up as the data lines are also used on the CPU itself, and the
whole data line is interconnected!)
For example, try grounding Z5 pin 17, causing the Test EPROM
to fail before the first flash. Or try grounding RIOT chip U5 or U6
pin 38 and see where the test program stops the LED flashing.
Always ground the pin BEFORE
starting the test, when the test is already running and in the
"continuous" flashing mode, the test will not go back and re-test
the RAM or RIOT select lines. Of course the outputs of the RIOT chips
can be shorted "on the fly", but that really doesn't demonstrate
much compared to the initial four LED test flashes.
Alternative to the test EPROM - the NOP Generator.
Larry Hammer (LHammerpin at verizon.net) came up with this neat idea that
applies to the 6502 system80 CPU board.
This test method has the advantage that it does not require a custom
EPROM to be burned. It also does not require any modifications
to the CPU board itself.
A very handy thing to have for debugging 6502-based system is a NOP generator.
As long as the processor has power and a clock, this should work.
The 6502 processor has an instruction set called NOP (No Operation).
The NOP tells the processor to cycle through every one of the 65536 addresses.
The end result is that the address bus will count in binary – each address
line being the square wave at half the frequency of the previous address line
(i.e. A0 will have the highest frequency, A1 will be half that, etc. all the
way up to A15, the lowest frequency). These are best tested with a scope, but
a digital probe can be used in a pinch. With a scope, all should be nice
square waves.
Building the NOP generator is easy, as long as the board has an EPROM socket
at PROM1 (all system80 CPU boards should have this).
First, get a 24-pin solder tail socket to plug into the PROM1 socket. Next,
get stiff, fine-gauge wire (cut off resistor leads work great). Push one
wire into the new socket at pin 12 – this will be the ground wire. Push
another wire into your new socket at pin 24, this will be the +5 volt wire.
Push a wire into the new socket at each data line pins 9,10,11,13,14,15,16,17.
This will be eight wires and the +5 and ground wires.
The NOP instruction is EA in Hex. That means you are going to solder the
wires from D7, D6, D5, D3 and D1 to the +5 volt wire. Then solder the wires
from D4, D2 and D0 to the ground wire.
This means that pins 14,11,9 will be grounded to pin 12.
And pins 17,16,15,13,10 will be hooked to +5 volts at pin 24
at the PROM1 socket.
Note that it is possible to assemble the NOP generator directly into the CPU board's
EPROM socket at PROM1 after the EPROM is removed. But do not do this!
The insertion of these wires into the EPROM socket will cause it to loose spring
tension and ruin the socket. Plus, if this is assembled into a spare EPROM socket,
it can be used over and over again on different CPU boards.
After this is assembled, remove the PROM1 EPROM and insert your NOP generator
into the PROM1 CPU board socket. Insure that it is properly oriented and that none of
the +5 wires are touching the ground wires.
Disconnect all plugs to the CPU board except for J1 (the main power plug).
Power up the machine. Alternative, do this on a work bench with +5 volts and
ground hooked up to the CPU board's J1 plug.
If you are using a digital probe, the following pins on U1 (the 6502 processor)
should be tested as pulsing:
| U1 Pin - |
Address |
| 25 |
A15 |
| 24 |
A14 |
| 23 |
A13 |
| 22 |
A12 |
| 19 |
A10 |
| 18 |
A9 |
| 17 |
A8 |
| 16 |
A7 |
| 15 |
A6 |
| 14 |
A5 |
| 13 |
A4 |
| 12 |
A3 |
11 |
A2 |
| 10 |
A1 |
| 9 |
A0 |
The pulsing at pin 25 may be so slow that the individual pulses can be heard.
If all the addresses are pulsing, then check the other chips, U2,U3,U4,U5,U6
to insure that the addresses at those chips are also pulsing. If the
addresses are pulsing at the U1 CPU, but not at one of these chips, then there
is a broken trace.
Also check the address lines at Z10, Z12 and Z7 to insure they are not broken.
If one or more of these addresses are not pulsing, then either the CPU is defective,
or one of the chips that are hooked up to the address are pulling it down. If
you are lucky, your CPU is socketed. Then you could remove the CPU and bend the
one lead out of the socket. But since these boards were manufactured with the
CPU soldered in place, you are most likely out of luck.
The next best way to proceed is to take a sharp razor blade and temporarily cut
the trace in such a way that it is easily repairable with solder. Check with
a voltmeter to insure that the trace is cut and reinstall in the machine with
all plugs removed except J1. Use the digital probe and see if the address at
the CPU is now pulsing. If the CPU is now pulsing, then the CPU is good and
one of the other chips is pulling down the line. If the CPU is not pulsing at
this address, then it is likely defective and needs to be replaced.
If this address is not pulsing at the CPU, check the same address at one of
the other chips. If you are using a digital probe, it may now appear to be
pulsing, but that is likely a false reading. Take a 3.3k resistor and connect
one side to the +5 volt supply, and the other to the address at one of the
chips that now appears to be pulsing. The line as checked with a digital
probe should now appear as high.
If after cutting the trace, the CPU is pulsing, then it will be necessary to
determine which chip is at fault. This can best be done by repairing the
trace previously cut at the CPU with solder. Then follow the trace from
this address at the CPU and find where it splits. Cut one side of the trace
and test again. Using this technique, it should be possible to narrow it down
to the defective chip.
Finishing Up.
New Battery
To replace the original battery, add a remote three "AA" battery pack and a 1N4002
diode (banded diode end first connected to the pcb "+" pin, and the non-banded
end connected to the positive lead of the battery pack). The diode is used
so the recharging circuit doesn't try to charge the AA batteries.
Also the game will work fine with no battery. Not having a battery means that the high
scores and operating audits won't be saved. Personally, I find
this acceptable.
An installed memory back-up capacitor. After
the battery is removed, the traces are sanded
shiny. The negative lead of the cap is put in the
negative battery hole. The positive lead is bent,
and soldered directly to the trace leading to the
positive battery hole (since the positive battery
hole was too far away).
|
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Memory Back-Up Capacitors.
If one insists on having a battery (can't live without those high scores!),
I would recommend installing a memory back-up capacitor instead. These
capacitors will charge when the game is on, and slowly discharge to keep
the memory alive when the game is off. The advantage to these capacitors
is they never wear out, and they won't leak corrosive materials. The best
of all worlds in my opinion. The down side is the game must be on
for about one hour every month to maintain their charge. Also,
the game must be on for about eight hours continuously to initially
charge the capacitor.
Note that some CPU boards will work
better with a memory cap than others. This has to do with the exact
memory on the board, its age, and its exact manufacturing specs.
Some memory chips have different power consumption
rates, hence varying results can be seen with memory backup caps.
Some CPU boards will maintain their memory well with a backup cap,
and others may not. "Your mileage may vary" is probably a
good statement about memory backup capacitors.
When I installed
my back-up capacitors, the minus and positive leads were not labeled
on the cap. There was only a black line on the cap to designate the negative lead
(the CPU board is labeled; the positive hole has a "+" next to it).
Jameco (800-831-4242) sells 1 Farad memory caps, part# 142957,
$3.95 each, $3.49 for ten or more.
* Go to System 80 Repair, Part Two
* Return to the Pin Fix-It
Index
* Return to Marvin's Marvelous
Mechanical Museum
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