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Danke LEON - R.I.P

Repair method for CPU boards Bally and Stern type -17 -35-100 -200

Renewed version since 28.1.2002.

Version 3 since 3.8.2003.

Version 4 since 6.4.2006.

Especially for CPU boards BALLY and STERN type -17 -35 -100 -200 I wrote a very short program and put this into an Eprom 2716. You place this Eprom in socket U6 and test the 3 most important chips, U9, U10 and U11. No program roms or memory chips needed on the board. This is certainly very interesting, if the LED was on or off all the time what means that the initialisation test of the game roms does not work.

Using my test Eprom.

This Eprom has a short program which does:

Set PA 0 to PA 7 and PB 0 to PB 7 of Chip U11 and U10 HIGH and then LOW, over and over again (interval=1 second).

Same for CA2 and CB2 of U11 and U10.

This program does not lock-up. This means, if an output of a chip was bad, the program will continue to work. This way you're able to use a LED in series with a 2K ohm resistor, a multimeter or a logic-probe to read all outputs of chips and know if everything worked. To have some means of control that the program runs ok, we connect a Control-LED which will flash in rhythm with the test. The LED on the CPU-board will also flash, because it is tied to the signal CB1 of U11, this, of course, only if U11 was working normally.

This test checks only CPU 6800 (U9) and both 6820 chips (U10 and U11) and is not dependent on memory chips (U7 and U8) and of no game-specific Eproms (U1, U2, U5, U6)

Since 2/4/2002 there is an extension to this repair method that allows to test memory-chips U7, U8 and U13, you find the manual and the end of this page.

Of course clock chips U15 and U16 must work, also the chip for U6 (test-prom is put into U6)

At the same time, this means, if the program didn't work, only some components can be responsible for this. Even the "Valid Power" detector circuit may be out of service, the program will be able to start with a manual reset.


If you use the program on a CPU board OUTSIDE the pinball machine, then connect the +5 and +12 volt, 43 volt is not needed!

If you use the program, with the board IN the machine, remove connector J4 on the 'Regulator board' to avoid solenoids working all the time in the rhythm of the test.

Remove chips U1, U2, U5 and U6, also U7 and U8.And, to start also remove U10 and U11.

Because the test-Eprom is a 2716 the program eproms in the board must be also 2716 types. If you are dealing with a board with its original ROM chips than use a really simple adapter, and place the test eprom in there.

REMARQUE; If you have a CPU board with an eprom type 2732 in U6 (for example Eight ball the luxe) you can use the test eprom 2716, it works fine!!!

The socket adapter:

You need this adapter only when using the test-eprom in a board that still has its original game ROMs installed.

Only 3 pieces of material are needed.

A 24 pins IC socket and two mini-hooks.

Bend the pins 18 and 21 upwards. Solder a wire to pin 18 (5 inch) ending on a black mini-hook. On pin 21 solder a wire ending on the red mini-hook. That simple.

The adapter ready!

When you need the adapter, put it in U6 and connect the black mini-hook on TP4 or ground, the red mini-hook goes to +5 volt on TP5. Of course you place the test-eprom into the adapter. This way the adaptation from rom to eprom is made. ATTENTION: this adapter will only work for the test-eprom, it can not be used to adapt a normal game eprom into a rom remplacement.

The Control LED.

The Control LED must be connected to address line 6. This is pin 15 of U9. Connect one lead of the LED with a green mini-hook to pin 15, the other lead of the LED is connected to 5 volt (TP5) using a 1 kOhm resistor. When you mount the LED for the first time, be sure the connection was ok. With the red hook already connected to +5 volts, touch the green hook to ground and the LED should light up. If not, interchange the two leads of the LED.




A severely damaged CPU board. These are the only components present on the board at the start of the test. On this CPU board I'm using the adapter.

First remove U10 and U11, minus two components that can cause trouble.

Put test chip in U6, (with or without adapter depending of the originals model of rom/eprom you have on the board) power up. +5 volts on pin 16 and 17 of J4, +12 volts on pin 12 of J4 and ground pins 18 and 19 of J4.

If the Control LED flashes in rhythm then you're lucky and you can check outputs of U10 and U11 (therefore replace U10 and U11).

No flashing ? Try a new 6800.

Still no flashing, manually reset by connecting pin 40 of 6800 U9 to ground for a moment, then check if there was +5 volts present on pin 40.

Next step is checking signals of U9. U9 pin 3 needs a clock signal (about 2,5 volts), if not check on U15 and U16 (see schematics).

Same for the second clock-signal on U9 pin 37.

Next signal is U9 pin 2 must be +5 volts. Then check pin 5 which should be around 2,8 volts.( oscillating signal). Pin 4 and pin 2 both should be +5 volts. And the last one pin 34, is a positive signal with very short negatives spikes. You can control this signal only with an electronic probe (or oscilloscope).

All of the address line signals from pin 9 to pin 24 (see schematics) are oscillating signals, except A8, A9, A10 and A13. Fhese four are negatives = 0 volt.

One of these signals should be bad if 6800 was replaced and is ok. Of course you can trace the bad signal to its source and repair it.

A last possibility is that the selection of U6 doesn't work, check the following pins of U6. Pin 18 without adapter you find here 2,5 volts (with adapter the pin is grounded). Pin 21 = +5volt. Pin 20 is at ground level with very short positive spikes, only to observe with probe or scoop.

If all these signals are ok, you have now a flashing Control LED! Once you are at this point, replace U10 and U11.

Now all outputs of U10 and U11 should go up and down.Check the outputs with a voltmeter or probe. If one fails connect it temporarily to the pin next to it. There are two possibilities: They both " dance" than the first output is surely dead and the 6821 must be replaced. They both fail, so there is a short somewhere on the output line. Disconnect the output line by bending the pin upwards and check if there is an output now. Now, if so, the 6821 is ok and the short is somewhere else on the connected line. If the output was still missing then the 6821 should be dead.

Conclusion; if all the ouput signals are there, now replace all the other chips ( except U6, the test chips is there, and U7 if you are working with an adapter, you can replace U7 if you are working without adapter.) The replaced chips should have no influence to the test. If not, there is something wrong with the selection of the chip, which somehow disturbs the test program.

Now you can put U6 back (and U7, if necessairy) and count how many times the LED flashes, (should be 7 times). Do not forget to replace the J4 connector on the regulator board! You are sure that U9 + U10 + U11 are ok, there are no shorts on the data and addressing lines. You can start to check memory chips and doubt program chips, depending on the number of LED flashes.

Follow the manual by Bally...

Test-program for Eprom can be downloaded here... For version 4 always use a 2732 eprom. It willwork fine in all boards , whatever type is in U6 2716 or 2732,Bally or Stern. Of course, if you still have an older ROM in U6 you will need the adapter socket as described.

Eprom can be ordered with me, price is 20$ or 15 euro...

Für alle, die keine Eproms brennen können oder wollen, gibt es fertige Eproms mit Leons Images hier im Shop

Extention to test memory chips U7, U8 and U13 ...



When for one reason or another you want to test your CPU on the test-fixture, you only need 5 and 12 volts. The 43 volt is only applied to test if this 43 volts was present on the pinball. Without 43 volt you won't get the 7th flash on start-up...

But when you make a connection between resistor 23 ( top) and resistor 17 (top) the CPU "thinks" the 43 volt is present and will fully start-up ( 7 flashes ) and work normally. How can this be?

Well, the 43 volt is reduced to 5 volt and then converted into a " impulses - train' this signal comes on pin 18 of U10 and from there the CPU can control the presence of this signal. So if the signal is present the 43 volt must be ok. By the connection we simulate the presence of the 43 volts by taking the " impulses-train " who acts as an interrupt for the display's and comes out of chip U12 and feed this via the normal circuits as the " impulses-train" normally created by the 43 volt. So for the CPU everything seems ok and allows the full start-up (7 flashes)!

Here, a CPU with the connection made, using two mini-hooks...

Danke LEON - R.I.P