Hi everybody,

I am repairing a WPC89 CPU board, that has a strange problem: Everything related to CPU data line D5 is stuck high. So I have lamp row and col #5 stuck on, three coils controlled by D5 stuck on, ground short at switch row 5 and switch col 5 always high.

Now the strange thing is, that the board boots fine, so D5 is OK in ROM and RAM. First I thought the problem is in U12 driving the driver board, but in that case switch matrix would not be affected.

The board had some slight battery leak damage, and so far I have replace U11, U12, U13, U14, U15, U17 and U20. Also tried with another WPC ASIC. Checking continuity of D5 from CPU to all chips is OK. Removing U12 results in lamps and coils not being stuck on anymore, so the driver board is OK.

Something keeps D5 high, but what - and why it does not affect ROM and RAM read/write?

Tuukka

There is continuity between all D5 pins.

But I think I just found the problem: Lamp and switch row/col are numbered 1-8, and data lines of course 0-7. So if my tester shows ground short row #5 and lamp row/col #5 always on, it really is D4 that controls them. And indeed there was discontinuity between U7/17 and U12/17. Added a jumper wire and now at least all the U20 inputs are strobing as they should. Tomorrow I will take the board to my WPC tester and see if it works.

It really is somewhat troublesome that in my gameroom with the WP tester I only have a multimeter and soldering iron, but to do any board work I must take the board home where I have a scope and desoldering station - but no WPC tester Maybe I should build a scaled down testbench with some LED's and buttons.

I'll be back tomorrow, with more info.

(It is kind of funny, that you can take days trying to solve the problem, but as soon as you explain it to others, you realize the solution!)

Tuukka

Board works fine now!

So, always remember the switch and lamp row/col are off by one, compared to cpu data line # !
And now, on to the next board...