SB16 (CT2290) Suddenly very quiet selectively and only playing certain instruments \ VOGONS

SB16 (CT2290) Suddenly very quiet selectively and only playing certain instruments

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First post, by ocdmonkey

Posted on 2020-12-06, 00:07

ocdmonkey Offline

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Ok, so something weird I noticed after changing out the VGA card in my HP Vectra is that the Soundblaster card I have installed in there doesn't seem to be working properly anymore. Depending on the application it will either be barely audible, or only play certain MIDI instruments. Jazz Jackrabbit in particular plays maybe half the instruments of its music (the main music track is almost completely gone), and the (I'm guessing) sample-based sound effects are barely audible. In Windows 3.1 the startup/quit sounds were super quiet but when I played a MIDI file it seemed to play fine at a normal volume. I thought it was some weird incompatibility with the new VGA card but I swapped it out with the previous one and it was still doing the same thing.

I'm honestly kinda at a loss of what to do about this. It's not the first time I've had some weird problem with this computer either (I was replacing the VGA card because the one I had been using before refused to display color when using my powered VGA splitter).

Reply 1 of 3, by Thermalwrong

Posted on 2020-12-06, 00:34

Thermalwrong Offline

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Since you've already tried swapping over the VGA card to no benefit, I suspect it'll be an issue with the solder on the pins of the main chip the CT1747. I've had similar things happen with an AWE64, though that was rather different circumstances and after I physically removed and replaced its main chip for reasons. At certain angles the card will play distorted audio, but if I flex it in just the right way, it works properly with everything.

This video has some good pointers on how to locate and fix loose pins on these things: https://www.youtube.com/watch?v=VUx7jZWkYQc

Reply 2 of 3, by ocdmonkey

Posted on 2020-12-06, 19:10

ocdmonkey Offline

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I've tested every trace on that chip I can see with a multimeter and they all seem to be fine. It would make sense for it to be a bad solder joint, since even in the short time I was testing it the symptoms weren't 100% constant, but I would really like to know for sure the source of the problem before I take a soldering iron to it. I'm tempted to stick it in the oven to re-flow all the solder but I haven't had good luck with that method in the past.

Reply 3 of 3, by mkarcher

Posted on 2020-12-06, 23:34

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Thermalwrong wrote on 2020-12-06, 00:34:

Since you've already tried swapping over the VGA card to no benefit, I suspect it'll be an issue with the solder on the pins of the main chip the CT1747. I've had similar things happen with an AWE64, though that was rather different circumstances and after I physically removed and replaced its main chip for reasons. At certain angles the card will play distorted audio, but if I flex it in just the right way, it works properly with everything.

The issue sounds like OPL3 synthesis working fine and PCM being too silent. Assuming this is not a mixer setup issue, and assuming PCM is not distorted, but just too soft, I would look for the issue on the analog side, so not the CT1747, but the CT1703-A DAC, the CT1745A mixer chip or the connection between them (goes via electrolytics, IIRC).

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