Ron wrote in message
...
On 04/12/2011 21:19, N_Cook wrote:
This is one of my repair briefs that may well be consistent with your
query
symptoms, causation would seem to be PbF or electrolytic intermittent
punch
through


Well that's an actual component failure, the fault I`m on about is
intermittent and very common. It doesn't seem to be dry joint or heat
related, sometimes they come on then go off, sometimes they fail to
produce sound even tho the meters show a signal.

Switching of and on again generally restores operation. It's become a
common fault and a shame because the units are otherwise very useful for
small gigs and if not for this lack of trustworthiness would be
lucrative for hire purposes.

I imagine that the typical case of output device failure might be caused
by the unit being thrashed beyond its design limits (as so often happens)

Ron

I would think thermistor TH810, Q801, Q805 and PS PWM controller IC804 are
just doing their job which is fine when amp is new but not when a bit of
dust and grime accumulates , component variation etc.

This is my earlier observation about the outlet fan , first air is directed
at a wall 3/8 inch from its blade, then forced through a very small grill
http://www.luthermusic.com/images/pr...1-original.jpg
The outlet grill , on this presumably later version, is under the master
control in the pic orientation.
This pic shows about twice the number of slots as the one I have here, so in
recent years they have punched more slots. This one is just the slots in the
black area of that pic, not the continuation towards the master control. I'm
not in the position to retrofit slots, but can bend and lift that corner
with a
standoff and elongated fixing hole.
The inlet holes are a line of 1.8 mm holes , directly under the top handle
in
that pic, so obscured."