Colecovision No Audio

[Aaron Spinks]

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? 

[ChildOfCv]

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).

[Aaron Spinks]

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? 

[Ikrananka]

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. 

[ChildOfCv]

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.

[Aaron Spinks]

Alright,  thanks for the info so I used frogger and these are the readings.  I did both DC and AC. 

[ChildOfCv]

Looks like it is trying to talk to the chip at least.  So it's quite likely that the sound chip is the problem.

[Aaron Spinks]

Any way to test the output from the chip or just replace it? 

[ChildOfCv]

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.

[Aaron Spinks]

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! 

[Ikrananka]

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?

[Aaron Spinks]

Yes pin 7 was 0 voltage on AC with frogger playing. I just double checked to be sure. 

[ChildOfCv]

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.

[Aaron Spinks]

Thank you!