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ColecoVision - no audio, only static even while playing games


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#1 Tidus79001 OFFLINE  

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Posted Wed Jan 16, 2019 12:45 PM

I recently purchased a untested ColecVision on eBay and the console is working, but there is no audio at all and the static noise is still playing from the PC TV speakers after the console is turned on. Picture and everything else works without issue. I have tried the following so far:

- Connected to a CRT using a RF adapter on the coax input
- Tried another RF adapter and cable, but still have the same issue
- Tested on both channels 3 and 4
- Issue is present with all games
- No audio at all (no sound effects heard competing simultaneously with the static)

Any ideas what is going on here, and how to resolve it. Is it likely that this console was an AV mod attempt gone wrong and that the seller is dishonest and was offloading it on a unsuspecting buyer who bought the console in good faith as being untested?

#2 sdamon OFFLINE  

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Posted Wed Jan 16, 2019 2:33 PM

I had a similar issue with a ColecoVision once that was resolved by opening up the top of the RF box inside the console and tuning one of the pots inside with an Allen wrench.  Might be worth a shot..  



#3 ChildOfCv OFFLINE  

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Posted Wed Jan 16, 2019 2:49 PM

Yeah, the audio modulator is definitely off kilter.  If you're lucky, it's just a matter of re-tuning the coil in the corner by the channel switch.



#4 Hannacek OFFLINE  

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Posted Thu Jan 17, 2019 2:35 PM

First try adjusting the pots in the rf box (see picture below). There are two pots, one is for video, and the other is for audio. If that doesn't work, your only other option is to do an AV mod. It is not worth it to try to fix the rf modulator, because it is too complicated and not worth the time. If you do an AV mod (and follow the directions that come with it), and still have no sound, then you need to get the sound directly from pin 7 of the sound chip. Ben Heck has instructions for that. https://www.benheck....site-video-mod/

Most of the time the problem is with the rf box, and can be fixed with an av mod. If the problem is with the sound chip, then the AV mod won't fix the problem, but usually the sound chip is not the problem.
 

mod1.jpg



#5 ChildOfCv OFFLINE  

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Posted Thu Jan 17, 2019 3:06 PM

First try adjusting the pots in the rf box (see picture below). There are two pots, one is for video, and the other is for audio. If that doesn't work, your only other option is to do an AV mod. It is not worth it to try to fix the rf modulator, because it is too complicated and not worth the time. If you do an AV mod (and follow the directions that come with it), and still have no sound, then you need to get the sound directly from pin 7 of the sound chip. Ben Heck has instructions for that. https://www.benheck....site-video-mod/

Most of the time the problem is with the rf box, and can be fixed with an av mod. If the problem is with the sound chip, then the AV mod won't fix the problem, but usually the sound chip is not the problem.
 

mod1.jpg

Oops, I guess I shouldn't just assume you're NTSC.

 

But assuming that's the case:  If you have perfect picture, do NOT adjust the RF coil.  That is the coil used in final modulation to a TV channel once all of the various signals have been created and mixed together (luma, chroma, FM sound).  Adjusting that will just remove what you do have.

 

The variable transformer in the upper right of this picture is the only one you should touch for a sound problem.



#6 Jinks OFFLINE  

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Posted Fri Jan 18, 2019 9:15 PM

If the rf is screwed you can not av mod. Trust me I tried. You will get a black screen. The av mod board does very little after the rf. Only way is f18a. I tried repairing my rf I replaced the chips on it and no avail. Did this after replacing the vram. Good parts coleco.

Edited by Jinks, Fri Jan 18, 2019 9:16 PM.


#7 ChildOfCv OFFLINE  

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Posted Fri Jan 18, 2019 10:49 PM

I can't comment on PAL or SECAM as I've never seen the schematics for either of those versions.  But on NTSC, if you have good picture on the RF, with or without sound, you can do the AV mod.

 

Of course the next alternative to waiting in the F18A queue is to get or build the RGB mod that someone (Ben Heck maybe?) came up with, and run it to the component video.



#8 NIAD OFFLINE  

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Posted Sun Jan 20, 2019 3:47 PM

The old AV mods for the ColecoVision improperly draw sound and you will get low volume output with the Opcode SGM and Exp. Mod. #1 Atari Adapter. You should draw sound for AV mods from the Cap at C88.... I think the left leg of the CAP if I recall correctly.



#9 SiLic0ne t0aD ONLINE  

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Posted Mon Feb 18, 2019 5:42 PM

NIAD is right. :) Get your sound from the cap @ c88, left leg.




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