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Old 15th January 2004, 08:41 PM   #1
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Default what is going on with my amp?

I am new here so if this is the wrong place for this question please let me know.

I have an old but hardly used Soundstream M3 amp (a three monoblock set from the mid '90s) two are fine but one block just stopped working (it had been working great). It blows a fuse on what looks like an overload/short protection circuit when the amp is turned on. (The fuse is either of two 5 amp fuses on a board right after the transformer.) it is doing this with nothing connected to the input or output. the fuse at the plug is fine and doesn't blow.

I can take it somewhere to get it repaired if I must but I would rather try to figure out what is wrong on my own and gain the experience. I have done some work with electronics but nothing like this.

thanks for any trouble shooting suggestions.

Luke
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Old 15th January 2004, 09:35 PM   #2
sam9 is offline sam9  United States
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Since the power entry fuses are not blowing, chances are there is a short on one of the internal PCBs. There are a lot of candidates for this. Others with more experience than me might have a quicker procedure than I do, but mine would be :

A-Visual exam to see if anything that shouldn't is touching the case -- loose wires etc.

With a schematic and component location chart in hand and a DMM

B- Check first the most obvious -- each component that is directly connected to ground to see if it has gone short.

C- Systematically check all components for possibly going short in order of what I think most probable order - diodes, Transistors (Collector/emitter), FETS (Drain/source), caps, eveything else.

D- If no shorts re-test looking for low resistance. Example a goog transistor will have a very high resistance (Megaohms) across the collector and emitter -- a low but not short resistance is an indicator.

Problems: -You may havr to remove some components to test them accurately. -The first bad component may only be collateral damage while the cause is elsewhere; replaceit and it just damaged again.

Anyway, if one is not experienced and/or brilliant the key is to be patient and systematic. Be willing to repeat the whole process if you don't find anything the first time. Success is not guaranteed.
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