McIntosh MC250 that caught fire

Ca_kes

New Member
So I found this MC250 online and thought it would be a fun project. As you can see it's a serious fixer upper. At some point there was a fire on one of the output boards :thumbsdn: The pictures are what it looked like after I cut out the bad stuff.
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Looking at it, it seems that one of the resistors catastrophically failed and caused it all to catch fire. I tried to look online but didn't find any information on this type of thing happening. I figure I'll definitely replace the output board, though I also considered point-to-point wiring but I imagine just buying a new board would just be easier. Any thoughts on this? I figure I'll also replace the electrolytic capacitors and maybe the same resistors on the other board (If this board's resistor blew-up, maybe the other one could?). Any other suggestions on replacments (e.g., Transistors)? I'm sure I'll end up keeping it until my next project comes up so I have both quality and resale value in mind. Thanks!
 

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Remember that smoke leaves all kinds of corrosive compounds behind that slowly destroy anything that its been deposited on. The question is how much this has/will effect the rest of the components in the amp even if they are not burned. At a minimum you're going to need to clean this thing very well, if that's even possible. Maybe other folks with more direct experience with fire and electronics can chime in.
 
Hmmm...fire is usually terminal since soot is conductive.

Might be difficult to get the unit to make spec again.

Good luck at any rate.
 
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Agreed

Yeah, looking at the way the fire went, all the smoke rose up through the heat sinks so all the parts on those will get replaced. I guess you could call me an optimist...
 
Looks more like a genius kept on upping the fuse value or manually pressed the circuit breaker until the sorted outputs destroyed everything.
 
I believe that everything is fixable, as long as the parts or equivalent are still available.

In this case, it is.

Agreed on the problem of the smoke residue.

But I think a good cleaning with a PCB/electronic friendly solvent will remove all.

I would go for it instead of recycling this unit.
 
I wonder how the clinic would have handled this.

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It is the II version. A new board will need to be built. You do not take on this type of project for resale value....it is either a labor of love or to learn a new skill set.

You have a lot, a lot of work to do before worrying about a recap.

When I see a unit this trashed I always try to reconstruct how someone could do something like this to a fine little amp. Most often when seeing something this wreaked it involves a band......and roadie repair.

DOB would have expected me to sell the owner a new amp or not hear the end of it.
 
Didn't know there were Mk-II with the early gen SS. Glass boards then?
Unit looks like a victim of the foiled fuse fix.

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This sounds like a project that would be harder and take longer than changing a rusted tube amp chassis with a new shiny replacement.
 
This sounds like a project that would be harder and take longer than changing a rusted tube amp chassis with a new shiny replacement.

The driver board would have to be dup'ed on perf board after a total cleaning of all the hardware and vetting of the xformers.

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Or, if one could get a decent image of an original board, it wouldn't be too hard to have some replacements run off from the numerous custom board houses.
 
its a pretty basic amp, manufacturing a new circuit board is definitely in order here, unless you can find a donor unit.

However it is easy enough to get a new one made, thats what I would be doing.
 
However it is easy enough to get a new one made, thats what I would be doing.
It would also be easier to close your eyes and buy anything off the bay and restore it. You wouldn't even have to ask a question to the seller as to whether it worked or not and he wouldn't have to worry about how it was shipped. I'd love to hear what AC would give you in trade for it toward another unit. :thumbsdn:
 
It would also be easier to close your eyes and buy anything off the bay and restore it. You wouldn't even have to ask a question to the seller as to whether it worked or not and he wouldn't have to worry about how it was shipped. I'd love to hear what AC would give you in trade for it toward another unit. :thumbsdn:

Its very easy to get circuit boards made up, the circuit itself is basic, it would be a good little project for labor of love or developing your electronic skills, and at the end of it, you have a MC250....Who cares what AC would give you, that is not the point of the exercise.
 
a pcb could be etched at home with a few cheap things and a steady hand .. this is how it was done in the old days ...trick is finding a board you can trace or work it out from the schematic ...there might even be an app for it these days ...:D
all the best in rebuilding it ...
 
Looks like the schematic is the 4th in the series. Part number from Mac parts is 039-063.

Lots and lots of current went through the emitter resistors and the sentry monitor circuit must have been tampered with as it got smoked also.
 
It is not that complicated of board, obviously a first generation just past point to point wiring. Could be easily laid out with a copper less breadboard and then point to point jumpering.
 
It is not that complicated of board, obviously a first generation just past point to point wiring. Could be easily laid out with a copper less breadboard and then point to point jumpering.

yeah thats what I was thinking, I have revived a few things with the old breadboard...
 
It is not that complicated of board, obviously a first generation just past point to point wiring. Could be easily laid out with a copper less breadboard and then point to point jumpering.
Have you ever done this for a unit you repaired?
 
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