You need to get an oscilloscope on the sound mixer section of the MPU. (Not the background sounds board)

Bigbad,

I have the same issue. My music is fine, but no sound effects or speech.

I'm told that something is wrong with the CPU board. I have minor alkaline corrosion but it is limited to only 10 or so components and all adjacent traces appear to have 0 ohms, I am lucky.

Possibly it's an EPROM, but I suspect discrete components instead.

I'm having my board inspected today, perhaps I can let you know what problems need to be fixed on my board.

Tim

OK, so I got a chance to work with Keith at K's Arcade in person.

My board has more corrosion than previously thought, so now I'm less optimistic, as my display PIA's are likely shot.

For the no sound/speech but music works issue... There is hope for my board, he found corrosion under the 6802 chip (U24) so that socket is definitely toast. My sound ROMs appear to be OK visually...

He will re-cap the electrolytics and replace the CPU socket, clean a little bit of corrosion and test. If the sound and speech returns, great, but there's more...

If the traces to the display header (from the PIA's) are OK, he might tackle replacing the PIAs. What appears to be a 'clean' board for me, isn't, even though 80% of it is working...

I hope this sheds light on the missing sound/speech issue. Good Luck.

-sigh-

*UPDATE*

Board has been repaired.

Corrosion caused the sound CPU to fail as stated above. Everything re-capped and display issues are fixed too.

What appears to "look OK" on the surface to normal people, often isn't "OK" to a technician with experience and proper test equipment! This is true with many other things, such as automobiles.

Surface corrosion shows up at the pins of the IC's as dull grey solder, instead of shiny silver solder. If you have board issues, or quirks, take a look under the socketed chips if you can.

I really lucked out this time, and continue to learn about these amazing machines, and the people, like you Pinsiders, who are passionate about them.

I had K's socket my RAM chip as well, so I can install NVRAM, which I ordered.

Should be playing machine later today!

Thanks for following.

Tim