Hello, community. Member for a long time, and have used the search with good results multiple times. This time, however, no luck. Let me give you a quick rundown on what's happening.
This is a standard Williams sound board, regular mods completed a long time ago. For comparison, I have 2 non working, and 1 that works great (it's in my TriZone machine). This board works great in Flash, so the problem is limited to the sound board itself. Power at IC11 (7805, 5 v regulator) is stable for a very long time (stopped after about 20 minutes, but it was perfect). 12v unregulated coming in is stable, measured after R27, and going into IC11.
2 boards have 6802 processors, TriZone has a 6808. The TriZone board works correctly, in the Flash machine, with all 3 processors, and all 3 ROMs. Caps have been replaced as a normal first step. I've even tried moving caps and part form the TriZone board to the Flash board, to verify they were still OK.
All 3 board tests produces the normal, correct sounds in both TriZone and Flash.
After initial power on, I can ground the sound pins (10J3, 2-5 and 7) and it will make the correct sounds, but only for about 30 seconds. It *feels* like there's something either not getting correct power, or failing. I'm at a loss which component to check next. I'm leaning towards the 6820 PIA, or the 1408 D/A converter.
Asking the wisdom of the community to guide me.
I really only have a DMM for testing, but I'm pretty good with soldering. I have no issues removing a 40 pin IC and replacing it - if I can find the replacement.
Thanks, much!!
Scott