Repairing Williams system 9 cpu boards

First i would like to thank Scott Morash (U.S.A.) He did the testing of the new test eproms on his Williams 9 board. I did not find any board and it was time to correct and replace the old test eprom version. The new version has now a memory test and also a new extra test eprom for the " sound" section of the CPU board .

This type of cpu board is really the change between older types 3 to 7 towards the new system 11 board. Only 3 pinballs have been made with this type of board: "Space shuttle , Comet and Sorcerer " All circuits except the power circuits are on this cpu board. So the cpu circuits, drivers for solenoids and lights, and sound (which has sound and speech) are on it. (However there is a small extra board attached for the speech.) Because this model was too complicated and to be able to add some extra output chips (PIA's), Williams has split up the design and from this system 11 has been made.

When I first got a board of this type ,I used the schematics of " Sorcerer" The schematics for all System 9 boards are the same so find the schematics here,...........



The goal of this article is to do basic repair on the cpu board itself and the 4 connected PIA's (6821). These PIA's pass all signals to the external circuits, displays, coils, lights, and via the switch matrix to all switches. The PIA on U15 is the source off the switch matrix. Afther these test are ok, we do a memory test. And if there is doubth about the sound section, there is now a second test eprom that checks the separated chips of the sound section. The sound section has his own CPU , extra PIA and memory. These + the amplifier chip can be tested using the new added extra test eprom . If the cpu memory and PIA's are working, then it's almost sure that the pinball machine will start and you can repair the rest (if necessary) using the build-in tests. If he still doesn't start-up then you'll have to check the program chip . You first have to check if all voltages are ok, which you can do with your dmm.. Don't forget to do this first !!


So your pinball machine does not start, but you checked all voltages and they're correct..

First remove the cpu board from the machine. If you're not sure where all connectors go, be sure to label them first ! Once the board is out of the machine, connect it to 5 volts.

Gnd connected at J17 pins 1,2 or3

+5V at J17 pin 4,5 or 6

Additionally tie +5V from J17 pin 4,5 or 6 to anode of VR1

At the right side of the batteries you'll find the zener diode VR1, and below it connector 1J17. Connect voltages to this connector, ground goes to pin 3, +5 volts goes to pin 4. You can also get 5 volts at pin 5 and connect this to the top of the zener diode. This can be seen on the picture. You also see a '0' on the display in the center off the board.



First you need my test eprom which you plug into U20. (remove the rom and keep it safe!) Like described in my other articles, the test eprom has a non-blocking test which brings all outputs of all 4 PIA's high (+5) and then low (ground) again. Using a dmm or logic tester you're able to check all outputs and see if there's one not working. If none of the PIA's works then the problem is more general. The display is connected to the PIA in U5, while the test program runs it will show alternating a 0 and a 7.

The test-eprom for the System 9 boards is an eprom 27128. The program for system 9 tests can be downloaded here, it is a zip file .. The checksum of this test rom is EDA2 . If you don't have an Eprom-programmer , find someone to burn the rom for you, or you can order one from me ....costs ....25 dollar.(postage included)

So if you're lucky then the display will show alternating 0 and 7 so you know the test is working correct.

There are 4 PIA'S ( U15, U14, U4 en U5), all pins from 2 to 17 have to go from 0 to 5 volt, which can be seen with a dmm. There are however a few exceptions ! PIA U5 pin 9 is not moving , this pin is grounded by a jumper. On PIA U15 are PA0 to PA7 used as input (pins 2 to 9), to see these move you'll have to connect pins 1 to 9 of connector 1J10 to ground.. then you can see the outputs move.

If one pin doesn't move, short it to the pin next to it. If they now both go up and down, then the PIA is broken, if they both don't move anymore, then or the PIA is broken, or there's a short on the exit which didn't move from the start. To know which of the two possibilities you have, you'll have to deconnect the output ( by cutting the trace (and repairing it afterwards again !!)) and check if he then goes up and down. If so then there's a short, if not then it's certainly the PIA which is broken.


......Worst case scenario...

If the program doesn't run then we'll have to start at the source, which is the CPU-chip-6802 itself. First replace the 6802, this is the fastest.. Use a 6802 of which you are sure it is working fine (or a new one). Same problem ? The jumper is at W12 and not at W11? Then check pins 2, 6 and 40, which have to be positive (around 4 volts). On pin 39 is a clock signal, on pin 4 IRQ; on pin 5 the VMA signal, and on pin 37 the E signal (synchro for external parts). These all have to be around 2 to 3 volts (measured with a dmm). They're alternating signals of which you can find some images below.





The clock signal .....................and the VMA signal


The E signal is almost identical to the IRQ signal..

If you find between these 7 signals not the right readings, then you have found the problem. Use the schematic to check where the signal comes from and trace it back to its source. This shouldn't be too hard, the circuits aren't complex. But you'll need the schematics....

The long road... or not!

What's left are the other outputs of the cpu, address lines (pins 9 to 25, except pin 21 which is ground!) and data lines (pins 26 to 33), but also the selection circuit off the test eprom U20 and the selection circuit of the pia's. If the program doesn't work this can be because the test-chip isn't being found by the cpu, or the pia's haven't been found.... How to solve this ? amazingly simple !!!!

It's useless to give you the signals which you would find if the cpu works, as this is not the case. There I found this solution for. Remove the test-eprom from the board and start the board again. The cpu will now work without a program, and run through all its addresses from 0000-0000-0000-0000 to FFFF-FFFF-FFFF-FFFF over and over again.. With this we can continue: all address lines should move. Measure pins 9 to 25 (except pin 21, which is ground), you should get 2 volts on each. Now we've checked all address lines. Now we're almost 100% sure the cpu works. If some pins don't move then it means they have a short. To test this, bend the pin up, plug the cpu chip back in and test.. if it works now then there's a short on this address line. Trace this by cutting the trace in several places until you find the chip which causes the error. The only thing which remains that can be wrong is the selection of the program chips or the PIA's, which we will check now.

The chip selection

We still work without prgram chip. Because the board goes through all addresses, every selectrion address of every PIA is also encountered. Selection pulses arrive on pins 22, 23, 24, 25, 35 and 36 of the pia's. You should find alternating signals, because the positive or negative side of the signals can varie in value, it's best to use the logical test-light which I have described in my page with " Tips and tricks " on my website. It's not always possible to check with a dmm, because some signals are very close to 5 volts, ( only a few milliseconds at 0 volt!!) so you don't see them alternate. With a test light however, both leds are working, one more then the other, but they have to light both..

The selection is being continued within the chips by the connected lower addresses, but we have already checked the address lines so we're sure about those..

A final case, if something is wrong with one or more data lines. If the above tests are ok, put the test eprom back in U20. The program will run but no data arrives at the pia's. Data lines of the 6802 pin 26 to 33 should move and measure 2 to 3 volts. Is one missing then check for a short. Don't forget that the 6802 has already been replaced so this can not be the source, so we have to have a short on a data line. Can be checked fast by bending the pin of the output upwards and check if the signal now is there on the pin.. If so then there's a short and the buffer is broken, because all data signals go through U23 which buffers them. Inputs are pins 11 to 18 and outputs pins 2 to 9. If the signals go in but don't come out, then the buffer is broken. If one or two signals don't exit, then probably there's a short on these outputs. If that's the case, you'll have to interrups a data line temporary and check which IC is the source of the short.. This takes a lot of time, but it really is the worst case...

Now we've finished and with this method you've got about 95% chance that the basic parts of the cpu work and the pinball starts-up .... good luck!!


Why don't we have to check the addresses when they arrive on the pia's ? same for data lines ? Because there are 4 pia's, the chance is almost 0 that none of the addresses arrive when we check if they leave the cpu.. same for the data lines.. there's only doubt in the address and data lines which arrive on the eprom in U20. This eprom is in a socket which may have bad contacts.. So do check the socket for bad contacts.

Memory check:

Added in June 2005.

To launch the memory test just push the SW1 located near 1J14. The alternating 0/7 on the display will stop ( can stop on 7 or on 0 depending at wich moment you push).Afther a short while it restarts 0/7/0/7..This means memory chip U 18 is ok.

If the display remains on a steady 7 or 0 the memory test indicates a memory fault. Nevertheless the memory test is running continously . We can check if the signals coming to the memory chip are ok.

Testing the sound section:

The sound section on the CPU board contains a separated CPU chip ( U11) a PIA ( U13) a memory chip ( U12) the sound eprom at U49, the amplifier is U59 and the D/A converter at U48 .

To test this circuitry we place a new test eprom in U49 .

Find the image here , it is to burn into a 27128 ..... The checksum of this test eprom is FC3E. You can use this test eprom also to test the sound section on a Williams type 11 CPU board. ( see the pages for Williams type 11 repair)

Before powering up the board, place back the normal game rom at U20 to avoid conflicts with the running test program. Afther power up check if the test is running at pin 15 of U11, the signal there is constantly changing from 0 to 5 volts. If not the program is not running. On the CPU chip ( U11) check the basic signals coming to the cpu chip , like the clock and reset are the same as the ones at the " normal" cpu so as that one was running ok , these signals must to be ok.

Now we suppose the program is running , test the output pins of the PIA ( U13) pins 10 to 17 they have to " dance" between 0 and 5 volts. Pins 2 to 9 will not move they are hold at 0 volt by a direct connection to the outputs of PIA U4. If the pins 10 to 17 do not move ,check first the selection signal of the PIA ( U13) at pin 23, we need pulses there . If ok change the PIA . If not check the selection chip at U8. Inputs are at pins 1,2,3 and 4 you need pulses at all 4. The output is at pin 14. Only pin 14 can be at 0 volt all others have to be a steady +5. If there is another pin coming to 0 volt the input is bad , if all stay at 0 or 5 volt the chip is bad.

I assume your PIA is working fine now, We now can proceed to check the amplifier and D/A circuitry.

To produce some sound, and test these we need +12 and -12 volt , Use an old PC power unit this tensions and the +5 volt are all coming from such a power unit. The following connections are needed

+12 at pin 9 of 1J17. -12 at pin 8 of 1J17, a loudspeaker ( 8 ohms) at pins 1 and 4 of 1J15, place jumper W10, and finally as we have no volume potmeter , jumper pins 1 and 2 of 1J16 , this will give us full sound. When connecting +12 volts always remove the temporally jumper between +5 and Z1.

At power up if all is ok you hear this ........ Sound like a rapid heart-beat, that is the transistion from +5 to 0 volts ...

If not check first the amplifier, touch with your finger pin 2 of 1J16. A loud humm should be the result.

If not replace the amplifier U59.

If the amplifier is ok and still no sound replace the D/A converter at U48.

Checking the sound memory at U12.

Push the SW2 button once ( SW2 is near 1J16) . The outputs of the PIA come to an halt and the sound will stop for a short while, then restarts , this means the memory is ok. If the sound does not restart the test is running continously on the memory test. Check the signals at the memory chip.

If the signals are ok , replace the 6810 memory chip.

Before placing back the board in the machine do not forget to remove W10 again !!!

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