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iridude

Channel 4 but not 3?

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I at least fixed some of issues with this coleco. It had no video or audio at all unless I put switch in middle. I took switch out cleaned it and soldered it back. I now have video but static audio on channel 4 only; channel 3 nothing. I think the RF board is shot any thoughts?  

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There are 2 adjustments.  In the center of the edge opposite the channel switch, there is the channel tuner.  In the corner near the channel switch is the audio adjust.  First examine both of them to make sure the ferrite slug is in good condition.  Then you can try adjusting them.  Use a hex wrench.  Advise you to first attempt to get the channel tuned in, then worry about the audio.

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2 hours ago, iridude said:

Any suggestions on how to fix this? 

4F06C9C8-77FD-44D7-9202-2A16629DA84B.jpeg

That could be an issue.  I think the pins are riveted brass, or some metal that doesn't care about solder.  I assume you already attempted solder?

 

Just theorizing here, but you may succeed with silver solder and brazing flux to reconnect those.

 

Otherwise you may just need to find a replacement socket with wires, or maybe perform one of the internal power mods so that you only need a single +12V supply or something.

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Posted (edited)

I did attempt to solder not holding. I was looking to see if perhaps digikey or somewhere had these no luck so far. I may look into internal power supply mod. I wonder if I can get the male pins somewhere.

 

I found replacement here:

 

http://coleco.freeservers.com/hobby.htm

Edited by iridude

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14 hours ago, iridude said:

I did attempt to solder not holding. I was looking to see if perhaps digikey or somewhere had these no luck so far. I may look into internal power supply mod. I wonder if I can get the male pins somewhere.

 

I found replacement here:

 

http://coleco.freeservers.com/hobby.htm

That's cool! I was going to suggest looking for junked TI-99's as they use the same plug on them as well. But I'm not sure how it was molded into the case of the TI so not sure it would physically fit the same. I believe I have managed to solder bare wire onto the centers of the posts back side in the past.

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Ok, I tried adjusting the RF channel 3 still no signal. I am wondering maybe Channel 3 dont work on modern tv? Unless RF Modulator no good.. I have no old tv to check.

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Posted (edited)

I guess you could concentrate on dialing in channel 4.  Get the video working, then adjust the audio.

 

But I see no reason for the generation of TV to change how channel 3 works.  It's always been specified to the same base frequency with the same audio sub-carrier and color sub-carrier.

 

Do other devices work on channel 3?

Edited by ChildOfCv

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Posted (edited)

How to adjust audio with small flat screwdriver thats what it looks like. I have no VCR, etc... no way to check lol

Edited by iridude

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11 hours ago, -^CrossBow^- said:

That's cool! I was going to suggest looking for junked TI-99's as they use the same plug on them as well. But I'm not sure how it was molded into the case of the TI so not sure it would physically fit the same. I believe I have managed to solder bare wire onto the centers of the posts back side in the past.

It dangles loose on the TI in the same manner ;)

 

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Pin 15 is actually D5.  It's one of the 8 data lines that the various chips send and receive data on.

 

Does your CV work when you have a channel sort of tuned in?

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Yes it works but sound sounds like no signal only channel 4 comes in. What would cause channel 3 not to work? Capacitor? Resistor? Lm1889 chip? Or something else. I should check rf out voltage when it’s on channel 3 vs 4 correct?

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RF output voltage will be tiny, since it's supposed to be comparable to receiving a signal on the antenna.  Your meter probably won't have any useful readings.

 

There are 2 capacitors, 2 resistors, and the tunable coil responsible for the channel itself.  If you have video out, then the LM1889 and most of those components must be working.  One thing you can do is reflow all of the connections in the RF box, as it is unlikely that any of the above simply failed.  More likely, there is a broken solder joint somewhere.

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I took a working RF Box and wired it to the non working coleco. Now I get nothing no signal.. I checked all traces and seem fine. The RF module is for a different Revision I dont think it matters but throw that out here. Pin 4 on J4 showing 12V so I know getting power. What should I check here. Or do I need a scope in order order to proceed further.

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Ok the old one says 75745 revision F; the one that I replaced with says 75745 revision E it looks a bit different. The video turn thing is for sure different. 

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Looks like my soldering not good that goes to pins of the j4 connector of the Rf Modulator. I am going to try something and hope it works. I am getting signal now but not clear it's like greenish and fuzzy.

Edited by iridude

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Basically, I rewired everything and I am going to move the RF box and do the AV mod is next. I am guessing should get some foam and copper shielding tape for bottom. I have it working now but does this look right? 

download (2).png

Edited by iridude

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