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Post by soop on May 6, 2019 12:35:25 GMT
Got a weird situation with a duo. I've measured everything in the sound circuit and it's all within spec apart from the opamp ic506. The input voltage is fine, but then the other pins apart from pin 4 (ground) are all off, and all fluctuate. *Actually pin 1 is a solid 6.8, which is about double. traces seem finee, and I've checked all the vias around the opamp. I've cleaned under the ic, and replaced it with brand new and a known working chip. All caps are replaced.
Any idea what could be causing this?
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keithcourage
Punkic Cyborg
https://www.facebook.com/turbografxfan/
Posts: 231
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Post by keithcourage on May 12, 2019 20:42:57 GMT
There has to either be a bad trace for the power 3.8V or a bad ground. The ground for that op amp goes bad quite a bit. Try touching a wire from a ground to the ground pin temporarily and see if the sound kicks on.
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Post by soop on May 13, 2019 11:12:02 GMT
There has to either be a bad trace for the power 3.8V or a bad ground. The ground for that op amp goes bad quite a bit. Try touching a wire from a ground to the ground pin temporarily and see if the sound kicks on. awesome, I'll try that tonight! keithcourage just tried it, and indeed touching any pin on that op amp to ground gives me a quick burst of sound. Definitely the game music too. How do I go about fixing it? I'm sure I tested continuity to all the traces and they're all good. I even tested the vias around it, but I'll double check I guess.
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keithcourage
Punkic Cyborg
https://www.facebook.com/turbografxfan/
Posts: 231
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Post by keithcourage on May 16, 2019 6:53:43 GMT
Sorry for the late reply. Just run a wire from the ground pin to the ground strip just to the side of the op amp. That is where the trace goes anyways. Simply scrap off a little green to expose the copper and bridge a wire. Here is a pic. Red line is to fix the ground. Blue line is to check for 3.8V on each point. I've had to bridge that with a wire before as well. postimg.cc/kR5yVBmrIt's kind of ridiculous how many weird symptom/damaged areas there can be in these DUOs. I've worked on so many of them now that I have most of the usual places memorized but there are still some in odd places that give me a challenge from time to time.
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Post by soop on May 16, 2019 19:20:07 GMT
Dammit. Just checked the continuity on all those pins and they're all fine. Any other ideas?
I think it might be because when I was tapping the pins on the chip, it wasn't just ground, it was any of them I connected to ground gave me a burst of sound. I guess that could be something else
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keithcourage
Punkic Cyborg
https://www.facebook.com/turbografxfan/
Posts: 231
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Post by keithcourage on May 20, 2019 11:04:01 GMT
Usually if that happens it's the ground or no power to one side of the power trace for the amp.
If not then it's a bad/shorted out via. Try putting an extra cap lead through some of the via holes around the op amp area and see if the sound kicks in.
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