Trace Elliot AH350 repair questions

Juseq · #1 08-07-2011, 06:34 AM

Hi! I hope this is the correct place to post this, I understood so by reading the stickys in the repair-section.

I have a broken Trace Elliot AH350 head, the model is probably AH350SMX. It's almost like this one : Trace Elliot AH350 AH 350 GP12 GP 12 SMX bass amp head - Guitar amplifier bazaar world. But it's only the thing inside (maybe it has been in a rack?). It looks just like RAH350 without the lower part.

Anyway, to the point! It's a broken one. It burns the fuse every time when powered on. I have some experience with electronics and I think if I get some diagnostics help I can fix it myself (it there isn't a huge problem). I've opened it and nothing looks fried, there is though some black mark on the left cooling unit in the thing that is screwed on top on it (sorry don't have a picture yet). Also, it had an 6A fuse inside, but I found out that there should be a 3.15A fuse. So maybe somebody has been using it with an fuse that is too large, does somebody have any idea what would be the first one to blow up inside, probably something in the power intake or in the power amp section?

And is it safe to unplug the preamp (it's attached with removable wiring) from the power section to see if it still blows the fuse? I think I'll take a few looks at it and if I can't find the problem I'll take it to some guy with more experience with transistor amps.

Thanks for your help!

RickenBoogie · #2 08-07-2011, 08:04 AM

Unless you are fully qualified and experienced working with amps, AND have all the testing equipment- you are much better off taking it in to someone who is. Honest.

BassmanPaul · #3 08-07-2011, 01:48 PM

Aus usual Rick is on the money. The root cause of the power fuse blowing is most often shorted output transistors. Take the amp to a tech and get him to fix it for you.

Jarrett · #4 08-07-2011, 03:37 PM

I had one too that was jacked up. Sent it to British Audio Service and now its right as rain.

exmaxima1 · #5 08-07-2011, 05:11 PM

Quote:

Originally Posted by Juseq

Anyway, to the point! It's a broken one. It burns the fuse every time when powered on. I have some experience with electronics and I think if I get some diagnostics help I can fix it myself (it there isn't a huge problem). I've opened it and nothing looks fried, there is though some black mark on the left cooling unit in the thing that is screwed on top on it (sorry don't have a picture yet). Also, it had an 6A fuse inside, but I found out that there should be a 3.15A fuse. So maybe somebody has been using it with an fuse that is too large, does somebody have any idea what would be the first one to blow up inside, probably something in the power intake or in the power amp section?

It is possible that you have a blown diode in the power supply rectifier section. If you can isolate the power supply from the rest of the amplifier (disconnect some plugs or wires), you can see if the fuse still blows----if it does, then you have a shorted diode or a bad power transformer.

A decent DVM will have a diode setting to check diodes and transistors. It will quickly find the bad component, and in many cases without needing to unsolder the parts from the board.

Good Luck!