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Produkte -> LEON: MPU System 7

Danke LEON - R.I.P.

Repair CPU boards Williams type 7.


At first I used on this board the tests for type 3/6, but there are some important differences. At first there is an extra PIA at the CPU board, and also the test eprom can not just be plugged in (2716 type) because the type 7 board works with a 2532 type game rom. Furthermore there are several jumpers which are different (according to the type of machine in witch the CPU was used). And the memory chips are other type , covering almost the same adressing , but the two memory chips take eatch half of the data bits. All these differences made me change these tests into a seperate part, otherwise it would become too complex. Fortunately type 7 boards use the same driver so this at least stays the same.

Type 7 CPU boards has space for 6 roms (eproms). three memor chips and two PIA's. This test will check the PIAoutputs and three memory chips. This will imply that the CPU chip is also ok, as well as the selection circuits. If the tests are ok then it's virtually guaranteed your pinball machine will start.

This is the Williams type 7 CPU board with battery holder at the bottom left.

As usual I use a test eprom which allows me to test all parts I just mentioned. Let's start with the setup.

Test eprom:

The test eprom is a type 2532, which you can download here: or buy here: <(version 3) This eprom fits without changes into the socket of IC17. Take care that jumper W11 is connected. If it's on W12 then you will have to move it.. ATTENTION: Since October 2003 there is a the new version of the memory-test . The test is more complete and there is an indication wich memory IC is tested visible on the "on-board" display (see memory test).


The only power we need to use the board is 5 volt. It needs to be brought to pins 3 and 4 of connector 1J2. + 5 volt on pin 4 and ground to pin 3. Also a temporary connection between C23 (bottom) and R3 (bottom) is necessary to start.

The test eprom, a 2532 type eprom you can plug in IC17.

To check how the test program works, we have to hook the control LED to pin 15 of the CPU chip (IC1) and the other side of this control led to +5 volts.

Again how the control led is made: a led with a resistance of 1000 ohms in series with 2 little hooks.The +5 volts, (bottom of condensor C23 left at the CPU board, and the green hook at pin 15 of the CPU chip IC1. To know it's connected well,at first use, put the green hook to ground, the LED should light, if not then switch the wires at the led.


Now you can start the tests. So what does the test program do ? It switches outputs PA 0 to PA 7 and PB 0 to PB 7 of PIA chips IC18 and IC 36 on the CPU board, and of PIA chips IC11, IC10 and IC5 on the driver board to high and then again to low. This all the time in rythm. The program is non-blocking, which means it will continue, even if one if the outputs is broken and does not follow. This way with a dmm, logic probe, or even a regular led (in serie with a 2k ohm resistor) you can measure all outputs and see if everything works. The same test -control you have with the 2 leds on the CPU boards, these are connected to CA2 of IC18 on the CPU board, if this PIA (IC18) works, these led's will also light in rythm. The display will also show a blinking 0 . The test really only checks the CPU 6808 (IC1) and the 6820/21 chips and is not dependant of the memory-chips (IC13 IC16 IC19) and certainly not dependent of the program eproms (IC26 IC22 IC21 IC20 IC17 or IC14). The selection chip IC15 and buffers of the address and data lines are also checked.

I just want to add that the PIA's are these chips which drive all pinball-functionality, like coils, lights, displays.

At the same time this means when the program does not work well, only a few components can be responsible for this.


The whole setup. You see the control LED connected to pin 15 of IC1 and +5 volt (C23 bottom) The +5 volts is also connected to R3 (bottom) using a temporary jumper.

If the control LED lights in rythm you're lucky and you can check the outputs of IC18 and IC36. If it doesn't light, then first try a new 6808. Still no luck ? Try a manual reset by connecting pin 40 of the 6808 to ground. Then check if there is permanent +4.5 volts present on this pin 40. It not, look for the source of your problem in the reset-circuit. For type 7 the reset circuit is made by transistors Q1/2/3/4/6/7/8 and 9. The output PA7 of IC36 will not move, as it's connected to ground by W25.

The next step when it doesn't work is check the signals on the 6808 (IC1), the clock-signal on IC1 pin 38 and 39. (clock signal is about 1.5 volts). Next thing to check is the signal at 6808 (IC1) pin 2 and 3 should be +5 volts. Finally check pin 5 which should have about 3 volts. Also check if the buffers of the address and data lines work, these are chips IC4, 3 and 8 for the address lines and IC9 for the data lines. On the schematics you can clearly see the inputs and outputs, which are drawn opposite of each other. I.e. A0 is pin2 IN and pin 3 Out. A1 is pin14 in and pin 13 out, etc. The signal which goes in should be the same as the one which comes out ! If the 6808 has been replaced and is now ok, then one if these signals should be bad. Just trace it to it's source and you should find where it's missing. A last possibility is that the selection of IC18/IC36 doesn't work, check if you get signals at the address lines of IC17, and selection signals on IC18/IC36 (pin 35, 36, 23, 24, 22 and 25). Now should all (or some) outputs of IC18 /IC36 go up and down. If there is somewhere an output on chip IC18 / IC36 which does not go up and down, then connect it to the one next it it. If this also falls away, then you have a short on that output, trace it first, if both outputs go up and down, then you can be sure the chip is broken. A last test is to put the program chips back into their sockets except for IC17. Their presence should not interfere with the working of the tests. If one if them does, it's bad. Conclusion: if all the outputs work then you can test your memory-chips.


If by a misfunction the selection of the memory chips IC13 and IC16 (tied together) stay low (0 volts) the test will not start, because, if the selection on pin 8 of these two chips is broken and the pin stays low the chips are selected and the memory data will corrupt the normal data on the databus. So whenever the test don't start up always mesure pin 8 of chips IC13 and IC16 they MUST be +5 volts at start-up!

If you also want to check the PIA's of the driver board then connect the driver board to the CPU board, put the test chip back into IC17 and power the board up. The leds on the CPU board will start to blink again.

Check if the outputs of the 3 PIA's go up and down. Remark: output of PIA IC11, PA0 to PA7 are always forced low. You can solve this by connecting ALL pins of connector 2J3 to ground (7 pins, connect to ground) and then these outputs will also 'dance' like the others do.

Once again, if there are PIA's which do not work completely, then check the selection of the PIA on its selection pins: 35, 36, 23, 24, 22, and check if pin 25 has 2.5 volts. If one of them is missing, then trace it to it's source, using the schematics, and a logic probe or o-scope. If only a few outputs don't work, again connect it to one next to it, if both don't work you have a short on the output, if they do then the PIA is broken.

Here you see the setup to test the driver board. Connected to the CPU, which has the test eprom in IC17.

Connector 2J3 on the driver board is connected to ground with all its pins.


Once you're sure the outputs of the PIA's work, you can use the pinball's own coil and lamp tests or use the repair method for the driver board on my site, to test that board completely.

Memory test.

Once the PIA test is successfull, you can test the memory chips, by pressing the button " diagnostics" once. This starts another part of my test program. Be careful, I once had a board on which the button did not work ! Then you can connect pin 6 of the CPU chip to ground (for a short time). Both leds on the CPU board will stop flashing (if they are on or off doesn't matter). (the display stops flashing to) Now check the control led connected to address line 6. This will stay off (timing) and then give you a few flashes. The first is for IC 13, the second for IC19 and the third for IC16. If all three appear then the test will come back on the regular PIA test and everything will start to flash in rythm. If a selection or a memory chip is bad, none, one or two flashes will appear. None means IC13 is bad, one = IC19 bad, and two = IC16 bad. Important: a "flash" means that the led clearly lights and goes off again. Faint lighting does not count as a flash.

To make things easy, you may also get our MEMORY-Tester if you need to test common RAMs on Pinball boards.

In version 3 the "on-board" display will show a 1 during test of memory chip IC13, a 2 during the test of IC19 and a 3 during test of IC16. When one of these is bad that number will stay " on", while the test still continously test that IC.

Depending on the diagnose it is best to just replace the memory chip. Also put in a socket so it's easier to change it in the future. If the test marks the same chip as bad, you'll have to trace the selection of that chip.

If the memory is bad, the test will continue to test on the same memory chip, so you can trace the selection signals easy with a logic probe or DMM.

I hope this detailed explenation will help you and wish you a lot of success!

Questions ? Email me ! ...