Dead channel with a caviat

[BigShooter]

Hi folks. This is my first post here, so forgiveness please if I miss some needed info. I have a Lafayette LR-85 receiver that has a dead channel. It's dead no matter the input, and it's dead at the speaker and/or the head phone jack. Here is the caviat... When the unit is cold the dead channel plays for a short time, like 15-20 seconds. If I turn it off, then back on, it plays the dead channel for about 3-5 seconds. All pots and switches have been cleaned. I'm guessing that because it works for a short time when turned on, it has to be a component breaking down? What is this likely to be? I'm thinking a cap or transistor, but I don't know which is more likely. Also, would this problem be limited to one specific board/area? If so, which one? If you've seen this issue before, please point me in the right direction. I am not a pro tech, more of a novice with a meter and soldering iron. TIA

 

[avionic]

Welcome aboard shooter.

 

[avionic]

Closely check for cracked solder connections in the failing channels power amplifier circuit.

 

[avionic]

Don't happen to have a service manual or schematic for this piece do you ?

 

[tcdriver]

Welcome to AudioKarma.

 

[swechsler]

Closely check for cracked solder connections in the failing channels power amplifier circuit.

That was my thought at first, but I don't think 15-20 seconds is enough to heat up the solder to affect a poor joint. More likely a bad component as the OP suggested. I'm going to guess a capacitor based on the difference in run times of cold start vs quick cycling. However, I'm not even close to being a skilled repair tech, so take that with several grains of salt.

 

[OMGCat!]

I like the bad solder joint theory. I've had a few that worked for a very short time then quit over and over again. Easy enough to tap around inside there with a chopstick to see if he can get the channel to come back. I'd especially tap around the top of the protection relay.

Definitely get yourself the service manual to familiarize yourself with the layout inside and what you're looking at. There are deadly voltages present in some parts and you don't need to be poking around in that spot as the receiver is working, just not exactly how it should.

 

[BigShooter]

Don't happen to have a service manual or schematic for this piece do you ?

Nope. Couldn't find one online either.

 

[peteCWA]

Nope. Couldn't find one online either.

We never did a service manual for the LR-85. The manual I offer has some service related info, but it's not service detailed. Personally for these types of problems, you need to have some service related experience. A scope would be very helpful in isolating the problem. Given the description of the problem, sometimes the "poke, push, tap" with a diddle stick (non-metallic tool) will also localize the problem.