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Unusual Marshall amp fault

N

N_Cook

Jan 1, 1970
0
Considering all those personal names of testers/inspectors labelled inside.
a 1962 from 2003. A history of blowing fuses then would work for months then
blowing again. Is there a name for them , the little bits of wire of
cropped-off component leads. Anyway under the tremolo valve base , probably
sort of spot welded just the solder blob end , to one of the tags. A 5mm
long piece of cropped off lead from a 1W resistor or similar. It could swing
across, as only vaguely atached, and short the tags between a cathode and
anode. I assume it was loose somewhere inside the amp and then bounced into
just the wrong spot and current passing was just enough to just "solder" in
place on the first shorting excursion
 
N

N_Cook

Jan 1, 1970
0
Wild_Bill said:
I've seen those waste ends many times although can't recall having to find
them as a result of a fault.

You're quite the detective, Nigel.

There were many boards where it was apparent that as part of the board
processing, it had been placed in some sort of fixture that would pass along
a belt sander-sort of arrangement to make all of the protruding leads a
uniform length.

The scratches of the abrasive were visible, and burrs formed on all the
leads were in the same direction.

I'd aways remove those waste tails/ends whenever I found them.. as some were
long enough to reach other solder pads, and frequently were over, but not in
good contact with adjacent pads.


Not really detective work. My repair methodology starts (after initial
powered up assessment if appropriate, then dismantling) with a full viewing
under a x5 illuminated inspection lamp+ bulbous lens. Noting unusual device
types, large R values if no schematic, state of solder joints, insulation,
discoloured areas etc. I just saw what initially looked like a non-cropped
off wiring-end ,through the valve base tag, ending too close to a pin 1 to
pin 7, bare cross-coupling wire. Up to then I was thinking mains transformer
interwinding fault.
 
W

Wond

Jan 1, 1970
0
Not really detective work. My repair methodology starts (after initial
powered up assessment if appropriate, then dismantling) with a full
viewing under a x5 illuminated inspection lamp+ bulbous lens. Noting
unusual device types, large R values if no schematic, state of solder
joints, insulation, discoloured areas etc. I just saw what initially
looked like a non-cropped off wiring-end ,through the valve base tag,
ending too close to a pin 1 to pin 7, bare cross-coupling wire. Up to
then I was thinking mains transformer interwinding fault.

Physical inspection is an important part of the diagnostic process. Good
eye.
 
C

Cydrome Leader

Jan 1, 1970
0
Wond said:
Physical inspection is an important part of the diagnostic process. Good
eye.

I always do a shake test, even with new computers to check for fallen out
screws, coins or other junk.
 
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