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Where to start on my Lafayette LR-221

Thanks, but no thanks. I have a surround sound setup in my room so it has to be at least 4-channel capable. I don't really want to use 2 stereo amplifiers so what I really need is an AVR. But I also care about looks too, and the Lafayette looks really good to me. I want to keep using quad amps/receivers because I also appreciate the history and engineering of them. This was also $20.

There was a brief time when it was completely fine. No hum, no crackle. Only very slight digital noise from my soundcard you could only hear with your ear pressed to the tweeter. That aside, it sounded good to me. I split hairs over speaker sound, not so much amplification sound.

This is also my learning project. I learn how to troubleshoot down the signal path. I increase my understanding of circuit topology and what certain components do, especially in a failing state. If I were to replace this one day I at least want to get it working well before I sell it.
 
DG_lite said:
Thanks, but no thanks. I have a surround sound setup in my room so it has to be at least 4-channel capable. I don't really want to use 2 stereo amplifiers so what I really need is an AVR. But I also care about looks too, and the Lafayette looks really good to me. I want to keep using quad amps/receivers because I also appreciate the history and engineering of them. This was also $20.

There was a brief time when it was completely fine. No hum, no crackle. Only very slight digital noise from my soundcard you could only hear with your ear pressed to the tweeter. That aside, it sounded good to me. I split hairs over speaker sound, not so much amplification sound.

This is also my learning project. I learn how to troubleshoot down the signal path. I increase my understanding of circuit topology and what certain components do, especially in a failing state. If I were to replace this one day I at least want to get it working well before I sell it.
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I would still dump it. If you want to learn, get something made in the last 20 years that is "relatively" easy to repair. You do not have the proper tools as pointed out by others and as acknowledged by yourself, or money as you acknowledged, to repair it, so you are just wasting your time and money imo. But if that is what you want to do, go ahead!
 
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Since I'm on campus, I do have access to O-scopes and signal generators in some of the labs now that I think about it. And very good ones at that. I just need to learn how to use them for these purposes.
 
Still, you are trying to learn on something that many expert techs would not touch, it is not just all the caps, transistors, and the power supply that are going to need replacing, you are still stuck with ancient circuit boards that are is sone state of failing.

If you really want to learn, start easy and work your way up. You are setting yourself up for failure with an impossible repair given your situation and level of experience.
 
UPDATE!!

I found the problematic component at last!

Turns out it was a transistor (Q18) in one of the SQ decoder boards (EPO-147B); one of the ones mounted on the underside. I found a replacement of the same type (2SK30GR) that should come in soon.

This caught me by surprise because I had no idea the audio signal passed thru the decoding boards unless the SQ option was selected with the function switch. I guess it makes some sense. But yes, freeze spraying that specific transistor makes the crackling go away when it cools all the way thru, and it gets noisy again when it warms up.

After that job, I ordered replacement caps for the preamp board a while back I still have to put in. I replaced one of the smaller capacitors in the power section and it changed how the hum sounded... slightly for the better. So I have a good feeling that the rest of the caps will fix the hum at last. Only problem is that board has lots of wires running to it and it's very hard to get into a good position to do soldering. I might have to cut some of the wires and solder them back together later.
 
The replacement transistor came in today. Same exact model, except made by Toshiba. And in case this one fails, I got a 4-pack, so 3 more left.

After replacing, I've been listening to Steely Dan's Gaucho and some Diana Krall crackle-free with my girlfriend, happy as a clam. How I've missed my desktop rig :)

Cap job is shelved until I feel like doing it. The hum is only apparent at high volumes, which I don't listen at. Not a huge issue as far as I'm concerned now.
 
Ladies and gentlemen, the hum has been BANISHED!

I don't know specifically which transistor(s) in the preamp section were bad, but I replaced 6 out of 8 and now there's no more hum that increases with volume. The old ones were 2SC900s which seem to have a somewhat mixed reputation here, based on my readings.

I ordered some KSC1845 transistors from Digikey and used those as replacements.

This case has now been closed. Finally. :music:
 
Naturally, the receiver now sounds clearer because there's no more hum interfering with the sound waves. I noticed when I first played some music.
 
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