Colecovision - suspected bad Rf modulator- no video, slight hum.

[amace]

I picked up a colecovision, but when I hook it up I get no video, and a slight audio hum. The video doesn't change at all, I just get the fuzz from channel 4. The audio slightly changes when powered on.

I have basic soldering skill, but not sure what to tackle. I checked the power supply with another coleco and it works fine.

My question is, would the composite mod bypass this and fix the issue? If so, that might be easier than trying to desolder the Rf board and find the issue.

Any other thoughts on what to check?

Thanks

[Steve W]

I'm not an expert on Colecovisions, but it could be a number of issues. I don't often hear about RF modulators going out, I mostly hear about chips going bad (have one with that problem, it has lots of graphics glitches) or sometimes the power switch needs work.

[amace]

I'm not an expert on Colecovisions, but it could be a number of issues. I don't often hear about RF modulators going out, I mostly hear about chips going bad (have one with that problem, it has lots of graphics glitches) or sometimes the power switch needs work.

I've tested the voltage coming off the switch in the on position and I get a consistent 12v and 5v off each side. As far as I'm concerned the power source and switch are ok.

I figured I'd try the composite mod first, then failing that replace the Ram chips.

Anything else to check other than broken traces?

I thought I'd try hook up audio direct from the sound chip and see if my TV detects it, that tells me if the issue is just Output, or maybe something else.

[bb_hood]

As far as I'm concerned the power source and switch are ok.
.

Check the power-on/off switch. Thats the problem with 95% of colecos... it happens to all of them at some point.

Ive owned at least 10 colecos, only one was working when I got it. The rest had broken power switches.

[APE992]

There are more voltages than 12v and 5v, I believe there is a -12v rail as well you should check.

[amace]

Following up on this (quite a while later, but oh well).

Turns out it was the channel selector switch in the RF Board. Something wasn't right, I reflowed all the connections and I started getting crappy video. Sometimes B&W, sometimes not. I realized then it cleared up when I took the case off and was able to apply pressure to the RF cable itself, so that told me there was a loose connection of some type. Went back and made sure every single connection was well soldered, with nothing grounding itself that shouldn't be grounded, and voila! It works.

While I was at it, I installed a composite mod, so I'm getting decent (as decent as the CV can output) video and audio now.