Unusual Marshall amp fault

N

N_Cook

Guest
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
 
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
Click to expand...
Heh... good catch!

I once had to debug a NAD stereo receiver I'd bought, used... bad
crackling and popping on occasion, especially when tapped or banged.
Like a lot of Japanese kit from a couple of decades ago, it had quite
a few through-hold resistors in a "vertical" mounting position. Two
had leaned, or been bend over just enough that their flying upper
leads could make contact... POP!

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
 
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.

--
Cheers,
WB
..............


"N_Cook" <diverse@tcp.co.uk> wrote in message
news:jbap0e$nhr$1@dont-email.me...
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
Click to expand...
 
Many of the old small transistor radios and similar portable gear from Japan
often had lengths of clear tubing on all the long leads for that 'vertical'
method of assembly.
Standing those axial-lead components on end was the early method of making
portable gear very compact.

I remember a radio which was only about 1-1/2" square and about 3/4" thick..
thin perforated aluminum speaker grille covering the front, and knobs on the
side.. much more compact than any other radio at the time, 1963 maybe.

--
Cheers,
WB
..............


"Dave Platt" <dplatt@radagast.org> wrote in message
news:kolnq8-gc3.ln1@radagast.org...
Heh... good catch!

I once had to debug a NAD stereo receiver I'd bought, used... bad
crackling and popping on occasion, especially when tapped or banged.
Like a lot of Japanese kit from a couple of decades ago, it had quite
a few through-hold resistors in a "vertical" mounting position. Two
had leaned, or been bend over just enough that their flying upper
leads could make contact... POP!

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Click to expand...
 
Wild_Bill <wb_wildbill@XSPAMyahoo.com> wrote in message
news:9joCq.59850$zC6.7674@en-nntp-15.dc1.easynews.com...
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.

--
Cheers,
WB
.............


"N_Cook" <diverse@tcp.co.uk> wrote in message
news:jbap0e$nhr$1@dont-email.me...
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
Click to expand...

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.
 
On Sat, 03 Dec 2011 13:17:22 +0000, N_Cook wrote:


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.
Click to expand...
Physical inspection is an important part of the diagnostic process. Good
eye.
 
On Dec 4, 8:34 am, Wond <gboot.p...@gmx.com> wrote:
On Sat, 03 Dec 2011 13:17:22 +0000, N_Cook wrote:

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.
Click to expand...
In my youth I impressed the hell out of one of my dad's friends, just
because I spotted a break in a pcb trace in his broken transistor
radio. ("Let spam take a look at it. He knows all about electronics.")
A second with the soldering iron set it right.
 
Wond <gboot.phil@gmx.com> wrote:
On Sat, 03 Dec 2011 13:17:22 +0000, N_Cook wrote:



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