Arcade Collecting > Pinball

WPC sound board problem (A-12738)**FIXED**

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lilshawn:
A known working board from another pin works 100%. Swapped the processor, and the 2 yamaha fm chips and confirmed them working.

Bypassed the electronic z-pot so that's not the issue. Have some digital to analog converter chip to replace the DAC sound chip, but unable to source the voice convertor.

But since we have audio from 3 different areas and nothing from any of them, I'm inclined to belive something has gone sideways with the communication between the CPUs. Still unsure about the reset line, seems the circuit is randomly going low (possibly resetting the cpu) still searching.

Still banging my head... Time for sleep things are getting blurry

lilshawn:
Okay, we have a bad static RAM chip (U9). turns out the chip was causing the CPU reset line and it's associated circuit to randomly dip low causing the CPU to be in a continual state of limbo. (tested with logic probe and oscilloscope at pin 37 of the 68B09 CPU should read high, was reading high/low/pulse indicating was being pushed into reset continuously)  The Main CPU must have been timing out and giving up waiting for the soundboard CPU to become active.

only found it after finding out that my EPROM programmer (which i was using to burn a set of sound ROMs to send the soundboard out for repair) will also test 74 series chips and also SRAM...SWEET! after testing all the 74LSXXX chips and found them to be good, i removed the 6264 SRAM chip at U9 and tested it. BAD!

pulled a working SRAM chip from an old board and we are back in business. if anybody thinks any other info i can add that would be helpful in assisting someone else, i can add it.

Ken Layton:
I'm working on one of these sound boards in an Addams Family.

Just tried swapping in a known good 6264 ram chip and it did not fix mine.

Back to the drawing board.

Ken Layton:
I have even swapped in brand new crystals on this one and it still doesn't work. I give up on this board so I'm shipping it off to K's Arcade for repair.

lilshawn:
Good try. Sometimes  the 78hct250? 257? ...Chip (right next to the biggest ribbon cable) goes bad. It handles the data in and out of the cable and is fairly susceptible to static.

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