N_Cook wrote in message
...
Last week I confirmed that the over-temperature sensing cct worked and the
triac cut the supply to the mains transformer. This is a Carlsbro S600M I
can find no info on . I was running on a variac and with about 90 percent
mains and with no load etc there was 0.1 amp current drawn from the mains
and a noticeable amount of transformer noise I took to be saturation noise
and current drain, more than I'd like but until I could confirm with the
owner about previous useage, I let be for then. This time I powered up and
1
amp being drawn with no load at only 70 percent mains. Disconnected the
secondaries from the amp and still the same.
Disconnected triac circuit and the transformer is happy to 100 percent
mains, fed directly, and only few mA of current drawn. What can be going
on
? To get to the triac componentry proper requires a major strip down
first.
Could it be half cycle firing and causing some sort of magnetic
mutual/resonant/self-induction effect that is causing excessive current? A
matter of isolation transformer and scoping some dropper in line with the
primary to see ? No obvious heating on the triac, only a small heatsink. I
was monitoring the DC last week and it was already a bit over the 63V
rating
of each electro. This time direct to mains, no triac, it was much more
normal, forgot to note but about +/- 55V probably at 100 percent mains



Scoped the secondaries and a cross-over distortion developes on increasing
the variac voltage, not particularly strongly, but definetely there, and
increases with voltage increase and "saturation" current/mechanical noise.
Placing an isolation transformer on the primary with a 25R/20W dropper to
"neutral" and scoping, then the problem was obvious ,now unfiltered by the
transformer. Could now run up much higher variac voltage because of damping
by the added R but even then there was 3mS duration spikes of peaks twice
that of the mains ac pk-pk of mains (UK) 20mS period. So some sort of bucky
inverter effect going on. What to look for around the triac when I get to it
?. To get to triac area, 8 XLR connectors with 3 stout wire standoff
conductors each to cut, probably by grinding through the most enclosed ones
(then desolder both cut ends and replace eventually ). Because audio input
and output and mains control all on the same board with no obvious isolation
band between the sections


--
Diverse Devices, Southampton, England
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