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Luxman A-373 - Powers on but no sound

Here's the remaining pics. Shows my setup too if anyone wants to sanity check that I've done it correctly. Thanks!

DSC_1095.JPG DSC_1096.JPG DSC_1104.JPG DSC_1106.JPG DSC_1113.JPG DSC_1115.jpg

Imgur album of all pics here where you can right-click > 'Open image in new tab' to see high resolution versions:
https://imgur.com/a/obPjSSl
 
Looks like something going on here. Looks like it was wired to bridge foil gaps. This could very well be your whole problem.

lux.JPG
 
Oh man, seriously?
I saw that board and yeah it looked super crusty but I figured it was some video input stuff that wasn't going to be used anyways so didn't think it would cause a problem.
Let me take a closer look at that. I noticed underneath is that there's a little capacitor leg that has come loose from its post too.
 
When you hear a relay click, it is almost always a good sign that the power amp section is working fine and problems lie elsewhere hence this board that looks quite chopped up. Might have to follow all traces and make sure their paths are making the proper connections.
 
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002 said:
Oh man, seriously?
I saw that board and yeah it looked super crusty but I figured it was some video input stuff that wasn't going to be used anyways so didn't think it would cause a problem.
Let me take a closer look at that. I noticed underneath is that there's a little capacitor leg that has come loose from its post too.
Click to expand...

#Cademan: Very good! The eye of an experienced tech, I hadn't seen the repairs of the board yet.
 
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Hey gents - I had a look at that board and despite appearances, it *seems* to be OK. I actually even disconnected it completely and powered the amp on and it behaved identically.
I think I'm about ready to throw in the towel on this one

Here's a few other things I've noticed which I am a little suspicious of but could be nothing
  • When I power the amp on, the Standby light does not change status. Basically it always remains lit in solid orange as soon as the amp is plugged into the power outlet. Normal?
  • On the transformer, all of the pins closest to the rear of the machine appear to be connected to each other. Are they all ground terminals? These are the pins I'm talking about:
    upload_2022-2-12_18-34-53.png
  • The reason for this pic was that the grey and purple wires seem to have no life on them. Measuring DC voltage was reading basically nothing - millivolts.
    index.php
 
  • "When I power the amp on, the Standby light does not change status. Basically it always remains lit in solid orange as soon as the amp is plugged into the power outlet. Normal?"
Yes, that's normal, when on AC, the power LED is lit, when powered on an additional LED above the selected input should go on. I think the default selection is "tuner" (At least on my A377)
The fact that both power amps do not work indicates that most likely the problem lies in the part that both have in common and that's the power supply.
 
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I can only find a schematic of an A371, maybe this detail gives you more insight in the power supply section, but be careful, this is of an A371!
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Thanks guys - I ended up finding a schematic that is very close to the A-373 in the A-384. It has the same layout inside and even uses the exact same pairs of 2SA1492 x 2SC3856 transistors (it even has the same PCB silkscreen designations).
The major difference between the two models appears to be that the A-384 is some sort of hybrid design with a discrete tube PCB inside, but the A-373 does not have that.
www.hifiengine.info/luxman/a384serviceman.pdf

I need to study this manual I guess but if anyone wiser than me has some time to skim it and tell me some basic pointers on where / what to check that would naturally be very appreciated.

upload_2022-2-13_11-37-1.png
 
Hey all - I managed to track down the problem this afternoon thanks to aforementioned A-384 schematic (if anyone is working on this amp, that's the service manual you need).
What I noticed was that I was seeing ~18V AC on pins 1 and 3 (red and blue wires in the pic below) but after the resistors I was seeing nothing. The two fusible resistors (R601 / R602) were reading open. I replaced them and now the amp works perfectly. I ran it for 2 hours with no issues - hoping it was just a surge or some other shenanigans that took them out.

Thanks again everyone for your help. I hope this thread helps someone else in future.

upload_2022-2-13_17-40-28.png
 
Hi everyone,

I'm new to this forum and wanted to share my experience fixing my old A377 (it powered on fine, but there was no sound). I want to express my gratitude to @002 and Audiokarma. You pointed out my issue. I tested R602 and R601, and both were dead.

I replaced them with 2.2 Ohms 5% resistors (my local store didn't have 2 Ohms in stock), cleaned the PCB (it had accumulated dirt for over four years), and guess what?
It's now back in service. Kudos to you guys!

Regards,
Yacine
 

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Welcome @YadaYac - very happy to hear my thread helped you fix your Luxman too :)
When I saw the email notification on this thread, I thought to myself "wow that was so long ago" but looking now it was just Feb 2022! This was one of the first things I repaired and it's funny (embarrassing almost) to re-read some of the thought processes and deductions I had back then. I've learned a lot in a short time doing as many repairs as I could, and the members of AK have always been there when I got stuck on something.

All the best mate.
 
002 said:
Welcome @YadaYac - very happy to hear my thread helped you fix your Luxman too :)
When I saw the email notification on this thread, I thought to myself "wow that was so long ago" but looking now it was just Feb 2022! This was one of the first things I repaired and it's funny (embarrassing almost) to re-read some of the thought processes and deductions I had back then. I've learned a lot in a short time doing as many repairs as I could, and the members of AK have always been there when I got stuck on something.

All the best mate.
Click to expand...
Hi! I'm new here too and I have the A-384 that's showing the same symptoms.

I've been searching for months for someone who could fix it, which seemed impossible, so I took it upon myself to repair this amplifier.
After my first Google search, I stumbled upon this thread and was very relieved that I'm not the only one with the same problem.
I'm going to give it a shot, I'm getting a multimeter tomorrow and will report back if it's the same problem.
 
I couldn't wait and I went and bought a cheapo multimeter instead of waiting for my friend to lend me his.

I measured the resistors and yep they were dead, I replaced them.
After I reassembled the amplifier I switched it on, after waiting for what seemed like an eternity (the A-384 needs to warm up the pre-amp tube first) SUCCES! Oh did I miss the warm & smooth but powerful sound of this amplifier, I really thought she was a goner!

Thank you so much for sharing how you fixed it for us to see, you saved my beloved Luxman.
 
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