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post #1 of 3 (permalink) Old 04-18-2019, 09:17 AM Thread Starter
 
Join Date: Apr 2006
Location: Inverness, UK
Posts: 521
Marshall AVT50 u/s

Hello ladies and djents.

My trusty 13-year-old AVT50 Combo has packed in very suddenly. It powers on but there is no sound. Previously it was working and sounding absolutely perfect as it always has, turned up at a mate's house for band practice, plugged in, switched on and... silence.

None of the LEDs inside are lit, all components are intact with no visible damage, the internal fuse is also good.

The valve appears undamaged and emits a barely noticeable very faint orange glow when powered on - not sure if it should be brighter.

Might be speaker but I'm unsure - will dig out a battery and see if I can get anything out of it. Not convinced that's the problem as like I say none of the internal LEDs are lit, which to me points to something in the electronics.

Any ideas? I'm an electronics engineer (avionics) by trade so happy to swing a soldering iron and chips at it if need be.

Cheers

'87
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post #2 of 3 (permalink) Old 04-18-2019, 02:12 PM
 
Join Date: Feb 2005
Location: El Paso, TX
Posts: 2,638
Re: Marshall AVT50 u/s

Quote:
Originally Posted by Shredder87 View Post
Hello ladies and djents.

My trusty 13-year-old AVT50 Combo has packed in very suddenly. It powers on but there is no sound. Previously it was working and sounding absolutely perfect as it always has, turned up at a mate's house for band practice, plugged in, switched on and... silence.

None of the LEDs inside are lit, all components are intact with no visible damage, the internal fuse is also good.

The valve appears undamaged and emits a barely noticeable very faint orange glow when powered on - not sure if it should be brighter.

Might be speaker but I'm unsure - will dig out a battery and see if I can get anything out of it. Not convinced that's the problem as like I say none of the internal LEDs are lit, which to me points to something in the electronics.

Any ideas? I'm an electronics engineer (avionics) by trade so happy to swing a soldering iron and chips at it if need be.

Cheers

'87
could be your 12ax7 if it has never been changed, but I'd think it is a fuse. If you checked the fuses though, I am not too sure. You may consider checking for output voltage going to the speaker. If you aren't getting any voltage to the speaker it lets you know the problem is the transformer or before the transformer and not the speaker.


i just found this and it sounds like a similar issue. There is some good troubleshooting suggestions in there too.

https://music-electronics-forum.com/...ad.php?t=36380
j.arledge is offline  
post #3 of 3 (permalink) Old 04-18-2019, 03:28 PM
 
Join Date: Feb 2014
Location: Kansas
Posts: 1,958
Re: Marshall AVT50 u/s

Kind of sounds like a power supply issue. Like the higher voltage is there for the tube, but not the lower voltage for the control circuitry and op amps. If you can get a schematic or identify the voltage regulators and check for output, that's always good start.
FireEagle is offline  
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