Diagnosing a bad Colecovision A/V mod

[GarrettCRW]

So, I purchase an AV-modded Colecovision (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230199004513) on the 'Bay and receive it in the mail today, and the picture is less than ideal. (We'll ignore Likely Error #1 here for a moment.) So, I crack it open to find electrical tape holding together some of the leads, including the white, black, green, and red leads from the audio and video jacks (white & black: video, red and green each to one audio out jack) to the chip label U20 on the Motherboard. The black and white leads are soldiered to the second pin from the right on the bottom side. The red and green leads aren't soldiered, and when left free, the sound functions, but the picture is snowy. When linked to the black and white leads, the picture corrects itself, but at the loss of sound. Additionally, the picture is fine without the audio cables plugged in. Is there a way to quickly fix this, or should I start giving the seller all sorts of hell?

[InsaneDavid]

should I start giving the seller all sorts of hell?

Yes you should! It's BS mods like this that make quality mods all that much harder to sell. It's also the reason I take pictures of the internal work when I do a mod. I wish I could help you but the CV is one of those consoles I don't poke around inside much. However from adding RCA jacks to Genesis systems my guess would be that the grounding is all screwed up on the mod in that Colecovision. Retying the grounds (outside part of each RCA jack) together and then to a solid ground in the system may fix the interference problem. From you're post I'm gathering that only one of the audio jacks is even wired? Although it outputs mono only the mod should at least split the mono output between the two jacks for mono through both speakers. I've heard that the CV composite mod doesn't require the audio jacks to be grounded (they'll ride the video cable's ground) but in my experience everything should be grounded as locally as possible.

EDIT: Ah, found it. My guess is the person you bought the console from used this mod (http://www.benheck.com/Games/Coleco/Video_Mod.htm), and executed it very poorly.

[GarrettCRW]

However from adding RCA jacks to Genesis systems my guess would be that the grounding is all screwed up on the mod in that Colecovision. Retying the grounds (outside part of each RCA jack) together and then to a solid ground in the system may fix the interference problem. From you're post I'm gathering that only one of the audio jacks is even wired? Although it outputs mono only the mod should at least split the mono output between the two jacks for mono through both speakers. I've heard that the CV composite mod doesn't require the audio jacks to be grounded (they'll ride the video cable's ground) but in my experience everything should be grounded as locally as possible.
I looked at it again, and both audio jacks have cables running from them-green and white from one, and red and black from the other, all leading to the sound chip. And, as it turns out, the black and white combo wasn't soldiered, either. I'm really too annoyed at this point to consider unscrewing the audio jacks in an effort to figure out the correct wiring scheme.


EDIT: Ah, found it. My guess is the person you bought the console from used this mod (http://www.benheck.com/Games/Coleco/Video_Mod.htm), and executed it very poorly.
That's precisely how the inside of this CV looks. Well, except the transistor, which is at an angle, very much in opposition of what the instructions say should be done.

[GarrettCRW]

UPDATE: I've given up on trying to fumble through correcting the audio end of this mod. Is there someone willing and/or able to take a crack at it for me?

[weirdguy]

I would check it if I was close to you.Take some pictures and I'll look at them.

InsaneDavid is probably right on the ground diagnosis. This mod is so easy to do, I don't understand why people don't care a little more when doing it.

[PingvinBlueJeans]

Take some pictures and I'll look at them.

Since he's been banned, I don't think he'll be posting pics any time soon. ;)