Believed to have been making an "electrical smoke" smell but performed
faultlessly for a gig, just general smokey smell , nothing specific to this
amp, I am trying again to find out why this amp is supposed suspect and not
anything else.
During the gig the stage supply tripped out. Nothing found amiss and powered
up lights and amps and continued .

No discolourations / open Rs/ open user or 7 internal fuses etc. Removed the
Zobell R and it is .8R rather than 1.5 ohm , but I don't think is
discoloured enough to have been burning.
No disc ceramics etc between ground and live / neutral.
Filter block X2 type 375V ac across L-N marked .1uF R .46 measured .024uF on
C and 1.2K on R scale on 1KHz RLC meter. Now hacked into and no sign of
smoke or overheating inside the cladding. It lays next to the dropper for
the mains relay and slightly discoloured cladding ,one-sided externally,
from that proximity probably.
Currently exploring the power amp which looks fine but in case one or more
transistors has gone open circuit and brief enough short circuit to trip the
mains trip but not any fuses .
No trace of smoke around the large mains Tx but will unbolt to check
underneath.
Any other suspects that would leve no trace?
How to find a problem , if there is not one to find?

Tried a new X2 on the same meter, marked .1uF + 100R
this measures .1uF on C and 140R on R range, perhaps a bit more hacking
into the original , maybe there is a trace of brown around the pins

I don't think there was a resistor in the original mains filter .
Hacked in , breaking the sort of sintered looking
metal at the leads leaving the metal to the capacitor at each end and 0 ohm
lumps that hold the leads.
I sacrificed a .1uF-100R new one and a very definite 3 band 100 ohm .5W
ceramic/MO resistor in that between one terminal lead and the sintery edge
of the capacitor.

N_Cook Inscribed thus:

Believed to have been making an "electrical smoke" smell but performed
faultlessly for a gig, just general smokey smell , nothing specific to
this amp, I am trying again to find out why this amp is supposed
suspect and not anything else.
During the gig the stage supply tripped out. Nothing found amiss and
powered up lights and amps and continued .

No discolourations / open Rs/ open user or 7 internal fuses etc.
Removed the Zobell R and it is .8R rather than 1.5 ohm , but I don't
think is discoloured enough to have been burning.
No disc ceramics etc between ground and live / neutral.
Filter block X2 type 375V ac across L-N marked .1uF R .46 measured
.024uF on C and 1.2K on R scale on 1KHz RLC meter. Now hacked into and
no sign of smoke or overheating inside the cladding. It lays next to
the dropper for the mains relay and slightly discoloured cladding
,one-sided externally, from that proximity probably.
Currently exploring the power amp which looks fine but in case one or
more transistors has gone open circuit and brief enough short circuit
to trip the mains trip but not any fuses .
No trace of smoke around the large mains Tx but will unbolt to check
underneath.
Any other suspects that would leve no trace?
How to find a problem , if there is not one to find?

Exploding tantalum bead cap !

--
Best Regards:
Baron.

Unwrapped the X2 cap , 1.7m long with a meandering 80 percent continuous
spark errosion line along the length averaging to the middle but no obvious
burnt or melted patches. Whether thousands of instantaneous discharges would
trip out an MCB or imbalance RCCD/ELCB/ GFCI , no idea.

Owner had removed the cover and extracted a load of fluff from inside the
minor fan air path. 4 of the 6 close pasked emitter Rs had faded printing
plus the changed value Zobell , perhaps them seriously overheating was
causing the electrical smoke smell. Change the X2 and Zobell and externally
cleanable filter cloth going over the minor fan.
the main fan you can shine a torch through front to back to check for any
blockage

The mains Tx nut was loose but no smoke trails inside other than black
soft-plastic plasticiser, from the disc pads, leeching and brown staining of
2 bits of sticky tape that hold the white high temp covering tape winding in
place.