CR620 problem - powers up but no output

nekas

New Member
Hello everyone, New here of course and wanted to say hi. I have visited forums before and they have always been helpful. Have used them to fix my Mits TV successfully twice. I have done some searches here and found a few things that have been helpful and will continue to look. Great site BTW.

The CR-620 was my first receiver and it has worked flawlessly for years. Though it has not been my primary for many years I do get to listen to it when on vacation. But alas, on my last visit I was told it was not working. So hear I am.

All the lights come on, but no output from the speakers. Also noticed I don't hear the CLICK of the speaker delay. I am sure use to hearing that over the last 34 years. My first guess would be the relay of course. I am sort of like Jpowell1, not really knowledgeable reading schematics or circuit testing, but do have some great friends that have helped on my TV repairs. I do the research and they do the soldering and get wine in return. Good relationship.

I am rambling now. thanks in advance.
 
Measure the DC offset at r775 and then at r776 and see if the DC offset is high, should be close to zero. If it's low then I suspect something in the protection circuit. When I repaired one of these not long ago it was the cap responsible for timing. I believe C808 is the one in the 640 , 220uf @ 16v but I might be wrong.
 
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I bought a used 620 and the protection switch was bad, or at least it had a bad connection and had to be resoldered in. Mine still clicked though, so it sounds like you have a bad one. Search for my thread on it, I think someone provided a link to a place that sells them and the part #.
 
Nekas- relay's rarely go bad, I've worked on many receivers and have yet to replace a "bad relay" - less the one in my 2020 which was visably cooked (caused by a DC offset issue) . Poor solder joint makes more sense- or high dc offset keeping the receiver in protection OR a bad cap or transistor in the protection circuit.
 
Another prime suspect would be the outputs. If other testing seems ok, remove and test the 4 big output transistors. (left side of the receiver)
 
I am finally back into the receiver and having a hard time finding r775 & r776. I see it on the schematic, but not on the actual board. I havn't taken the receiver apart, just the cover off. Is it located near the front by the relay and the copper coils? I'm looking at the numbers printed on the top of the board. low 800' are by the relay and low 700's are around the coils. hmmm
 
ok, found them. One of them has 40vdc running across it. The other has 0. But I don't know which is which, but think it is r775.
 
Using an o-scope found that a signal is going in to the relay, but could not find a signal coming out anywhere. So, with a 40vdc on r775, would that mean the relay is stuck in protect mode.
 
ok, found them. One of them has 40vdc running across it. The other has 0. But I don't know which is which, but think it is r775.

You have a shorted output and/or driver transistor in whichever channel has the 40v. Zero volts is the good channel.
 
Using an o-scope found that a signal is going in to the relay, but could not find a signal coming out anywhere. So, with a 40vdc on r775, would that mean the relay is stuck in protect mode.

Yes. It is in protect mode. That means the protect circuit and relay is doing what its suppose to do.Preventing that 40vdc from getting to the speakers.
 
Yeah, looks like the right channel has the problem. So, just trace it back to the figure out the problem.
 
Need to check ..TR719,721,723 and 725 . One or more of them is shorted collector to emitter.
 
Is there a way to determine if the actual transitors 2SB531 and 2SD371 are bad. I had 40vdc at both there connections. Where do I find replacement parts?
 
Is there a way to determine if the actual transitors 2SB531 and 2SD371 are bad. I had 40vdc at both there connections. Where do I find replacement parts?

There should be 40 +/- at the collectors of each one.But almost zero volts on there emitters. Need to power the unit down and remove the transistors from the circuit.Then test them for ECB shorts. Can't accurately thest them in circuit...
 
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