Aaron Spinks Posted November 5, 2019 Share Posted November 5, 2019 I picked up a coleco and the video works but no audio comes through. My other two colecos work just fine with the same connections. I bought the composite mod from retrofixes.com and I still get video but no audio. After a lot of research I tried connecting the audio to C88 closest leg to the rf box, still no sound. I then tried connecting the audio cable to pin 7 on the sound chip and still nothing. Is the sound chip the culprit? How and what do I test going forward? Quote Link to comment Share on other sites More sharing options...
ChildOfCv Posted November 5, 2019 Share Posted November 5, 2019 The next thing to check is the voltage on pins 5/6 on the sound chip. (They're both tied together, so you probably only need to check one). Quote Link to comment Share on other sites More sharing options...
Aaron Spinks Posted November 5, 2019 Author Share Posted November 5, 2019 Forgive my newness but I'm still learning to use my multimeter. How would I check those pins with a multimeter? Or do I use the continuity tester? Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted November 5, 2019 Share Posted November 5, 2019 Turn the dial on your multimeter to 20 DCV - this sets the multimeter to measure DC voltage with a maximum range of 20V. Now hold the tip of the black probe to the exposed ground plane somewhere on the ColecoVision main board, e.g. the exposed silver area around one of the screw holes that hold the main board in the console. Alternatively, you can touch the black probe tip to pin 8 of the sound chip as this is also connected to ground. Now, touch the tip of the red probe to pin 5 or 6 on the sound chip. Report the voltage reading back here. Quote Link to comment Share on other sites More sharing options...
ChildOfCv Posted November 5, 2019 Share Posted November 5, 2019 5 hours ago, Ikrananka said: Turn the dial on your multimeter to 20 DCV - this sets the multimeter to measure DC voltage with a maximum range of 20V. Now hold the tip of the black probe to the exposed ground plane somewhere on the ColecoVision main board, e.g. the exposed silver area around one of the screw holes that hold the main board in the console. Alternatively, you can touch the black probe tip to pin 8 of the sound chip as this is also connected to ground. Now, touch the tip of the red probe to pin 5 or 6 on the sound chip. Report the voltage reading back here. An AC reading at the same range might also be useful. Also, make sure that the game is supposed to be making noise at the time. Those pins only do interesting things when music/sfx are happening. Frogger is my go-to for sound and video testing, for that reason. Quote Link to comment Share on other sites More sharing options...
Aaron Spinks Posted November 5, 2019 Author Share Posted November 5, 2019 Alright, thanks for the info so I used frogger and these are the readings. I did both DC and AC. Quote Link to comment Share on other sites More sharing options...
ChildOfCv Posted November 5, 2019 Share Posted November 5, 2019 Looks like it is trying to talk to the chip at least. So it's quite likely that the sound chip is the problem. Quote Link to comment Share on other sites More sharing options...
Aaron Spinks Posted November 5, 2019 Author Share Posted November 5, 2019 Any way to test the output from the chip or just replace it? Quote Link to comment Share on other sites More sharing options...
ChildOfCv Posted November 6, 2019 Share Posted November 6, 2019 Well, I thought you did, by trying to take audio directly from that pin. But you can test the voltage on pin 7 in AC mode and see if it's nonzero. Quote Link to comment Share on other sites More sharing options...
Aaron Spinks Posted November 6, 2019 Author Share Posted November 6, 2019 I tested the AC voltage on pin 7 and it was 0. I am assuming that confirms a bad sound chip. My next question is, will any sound chip on Ebay that is the same part number work? I have read about clones of these chips. Where is the best place to get one? Again thank you for all the help, I am learning a lot! Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted November 6, 2019 Share Posted November 6, 2019 2 hours ago, Aaron Spinks said: I tested the AC voltage on pin 7 and it was 0. I am assuming that confirms a bad sound chip. My next question is, will any sound chip on Ebay that is the same part number work? I have read about clones of these chips. Where is the best place to get one? Again thank you for all the help, I am learning a lot! Just to double-check, was the pin 7 zero voltage with Frogger playing? Quote Link to comment Share on other sites More sharing options...
Aaron Spinks Posted November 6, 2019 Author Share Posted November 6, 2019 Yes pin 7 was 0 voltage on AC with frogger playing. I just double checked to be sure. Quote Link to comment Share on other sites More sharing options...
ChildOfCv Posted November 6, 2019 Share Posted November 6, 2019 A matching part number is theoretically good. They were used in CVs, some arcades, Sega Genesis, and PCJrs at the time, just to name a few. The supply isn't overwhelming, but you might be able to find a salvaged one, or if you find one of the systems that have the chip for cheap... I'm less sure about eBay's and Ali's stock, but they're at least cheap and sold in bulk, so even if it's a counterfeit or not the best quality, one might work. Quote Link to comment Share on other sites More sharing options...
Aaron Spinks Posted November 6, 2019 Author Share Posted November 6, 2019 Thank you! Quote Link to comment Share on other sites More sharing options...
vintagegamecrazy Posted September 20, 2022 Share Posted September 20, 2022 Time to bump this topic. I'm having the same problem. I'm measuring off the C88 capacitor and off the pin 7 on the audio chip and am getting 1.61v DC and no audio. Is this indicative of a bad audio chip? Quote Link to comment Share on other sites More sharing options...
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