Marshall AVT50 eating fuses

[Kramer39]

Read in an earlier post that the power module may be blown. Is this the control transformer or something else? Have a few 1.6A fuses left....should I attempt a 6A?

[Jazz P Bass]

Do NOT attempt a 6 amp fuse!
The power module is attached to the heat sink.
The output transistor stands up off of the circuit board.
That is the part that is most probably at fault.

[J M Fahey]

As the label says: "Refer servicing to qualified personnel"
Sorry.

[R.G.]

First of all, let me say that what I'm about to say is not intended to belittle you. It's just the best advice for someone who has the degree of technical and debugging skills your statement implies. If you're really more skilled and experienced than that, take this as an apology and some discovery.

There is **always** a reason a fuse blows. In commercial production gear, that reason is *never* that it just needs a bigger fuse. Putting in a bigger fuse merely lets the fault current destroy something else. What's needed is a way to limit the current without blowing a fuse so the repair tech can find the problem.

The fact that there is a question about putting in bigger fuses means the person asking does not fully understand the problem. That's not me being sarcastic, just being realistic. So this is (I think!) why you got the comment about sending it to qualified personnel. There is a good chance of causing more damage with power devices if the repairer does not have a good background in the technology.

As a side note, I'm fascinated by the number of posts here which say pretty much "My whizzo-banger amp is not working, or popping fuses, or making smoke; it's probably the transformer, isn't it?" I don't know what it is that makes people want the problem to be transformers. It usually is not the transformer. Transformers are usually very reliable and tolerant of massive overloads. Semiconductors are generally intolerant of even milliseconds of conditions above their design maximums. But still people seem to want it to be the transformer. I find it curious that they think that.

[J M Fahey]

Dear kramer and rg.
I was not being sarcastic at all, but going just to the point.
That was reinforced by the well meant "sorry" at the end.
What worried me a little is that since this is s Forum chock full of well intentioned and informed technicians, in no time somebody would chime in with suggestions "change this or that" which are accompanied by measurements to check whether they are the right move or not.
It can lead to greater problems than the original one.
As a personal example: when somebody brings a dead/failing amp into my shop, I always ask: "is it untouched or somebody tried to repair it?"
If untouched, I look for the usual suspects according to the symptoms.
If previously touched by somebody else, I have the added complication of guessing what he *thought* had to be done and backtracking, and adding that that work was not properly done ... or the amp would be repaired by now !!!!
If the musician itself tried to do it, it can be even more complicated.
I often (always?) find misplaced transistors (pinouts differ or they were plain "read" upside down), misplaced ICs, diodes, bad value resistors (improperly read original value), bad solder, lifted/burnt pads and tracks, "I pulled these wires and don't know where to replace them", improperly set wire connectors, either in other sockets or in the same, backwards.
Yes, I know, there are little plastic guides to make reverse insertion impossible, but being "little" and "plastic " means they *can* be inserted the wrong way, just applying somewhat more pressure.
All said, AFAIK Marshall AVT power modules *can* be replaced as a block, with some precautions, no soldering or measuring involved, so kramer39 might try to replace it all by himself, with some coaching here.
Anyway, getting the help of a friend who at least has built a couple pedals or a small amp or similar experience would be invaluable.
A couple sixpacks or introducing him to that hot neighbour/friend of yours he's lusting after, will surely help.
Good luck.