N Cook wrote in message
...
Found another nasty under the ps board but don't think it is the main
problem.
This pair of wires to the speaker switch had one of the wires squashed
between a large W/W ceramic cased dropper under the ps and the chassis.
Melted through but as it cuts the earth to the speaker presumably no
problem
as such and wire not broken. But there is smoke blackening or something
grimy in that area but it could be a small electrolytic parallel to the
fan
cooked as it is directly over the large droppers and leaked electrolyte
but
all rather nasty. The aluminium of the chassis directly under this
particular dropper has a strange flecked grey corrosion or something that
probably more likely due to electrolyte rather than vapours off the
charred
PVC insulation. I don't see why this insulation has charred rather than
just
melted as the owner never switched this speaker switch, I assume somewhere
maybe ages ago it was open at some point
Anyone know the function of the big triac on the mains, crowbar operation
to
blow the mains fuse if too much mains power drawn ?, I've not traced any
triac associated line back into the amp that could trigger it as more
active
amp protection.
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
The corrosion i've photoed here
http://home.graffiti.net/diverse:graffiti.net/ali2.jpg
The overexposed T area is the mains transformer and the groove marked ""
was created by the squashed/trapped cable or exposed wire core probably
vibrating.
From "" to T only about 10mm so just 5 mm or so free gap to run these 2
speaker wires between mains torroid and high temp wire-wound dropper with no
added high temperature sleeving.
The grey flecking is what I'm assuming is electrolyte corrosion effect
rather than burnt PVC product.
If this fan lytic over the fan supply dropper leaked to short in use then
dropper would generate more heat as well so compounding as well as shorting
out the fan to the main amp heatsink. The owner had used the speaker switch
in the past, during sound checks. What a tangled web we weave.
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/