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From: N_Cook on 11 Nov 2009 08:00
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


From: N_Cook on 15 Nov 2009 08:08
N_Cook <diverse(a)tcp.co.uk> wrote in message
news:hdecfh$i7j$2(a)news.eternal-september.org...
> 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
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


From: N_Cook on 15 Nov 2009 11:25
What can go wrong with a triac control cct , visual and cold component test
of these comps shows nothing obviously amiss
TIC2360, BC214C,2x 1N4005,5V.1W zener, 2 thermal switches, 2x 100R w/w,
2K7,47R, 2.2uF 400V polyester and 2x 220uF,10V electros
I will have to draw it out as a schema


From: Jamie on 15 Nov 2009 12:03
N_Cook wrote:

> What can go wrong with a triac control cct , visual and cold component test
> of these comps shows nothing obviously amiss
> TIC2360, BC214C,2x 1N4005,5V.1W zener, 2 thermal switches, 2x 100R w/w,
> 2K7,47R, 2.2uF 400V polyester and 2x 220uF,10V electros
> I will have to draw it out as a schema
>
>
Triacs can develop latching issues and thus, depending on what you're
doing with them, they may take out a protection circuit (fuse), or
if used to select +/- outputs to generate a selective DC polarity, could
hang up on one side and this cause erratic behavior to the device
connected to it.

The transistor BC214, is a PNP type, know to open in the BASE/EMITTER
how ever, you've stated that you have done the cold test on that. The
other problem is, they lose gain and thus, what ever function they have,
they'll have no gain to perform it. This normally happens to a poorly
designed circuit or one that got over voltage, unexpectedly.

I would check the Zener to make sure it does have 5 volts across it
when power is on.

And also, Are you sure that is a zener? by the looks of the parts
list, I would say this may be a simple phase control device? Maybe you
have a failing DIAC/SIAC which can be past off as a diode? That 2.2 uf
Cap at 400V, is leading me towards that direction. Since that is a
common value for the trigger pulse on the gate which gets generated by
the DIAC.





From: N_Cook on 15 Nov 2009 13:39
Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> wrote in message
news:TfWLm.50451$gg6.23693(a)newsfe25.iad...
> N_Cook wrote:
>
> > What can go wrong with a triac control cct , visual and cold component
test
> > of these comps shows nothing obviously amiss
> > TIC2360, BC214C,2x 1N4005,5V.1W zener, 2 thermal switches, 2x 100R w/w,
> > 2K7,47R, 2.2uF 400V polyester and 2x 220uF,10V electros
> > I will have to draw it out as a schema
> >
> >
> Triacs can develop latching issues and thus, depending on what you're
> doing with them, they may take out a protection circuit (fuse), or
> if used to select +/- outputs to generate a selective DC polarity, could
> hang up on one side and this cause erratic behavior to the device
> connected to it.
>
> The transistor BC214, is a PNP type, know to open in the BASE/EMITTER
> how ever, you've stated that you have done the cold test on that. The
> other problem is, they lose gain and thus, what ever function they have,
> they'll have no gain to perform it. This normally happens to a poorly
> designed circuit or one that got over voltage, unexpectedly.
>
> I would check the Zener to make sure it does have 5 volts across it
> when power is on.
>
> And also, Are you sure that is a zener? by the looks of the parts
> list, I would say this may be a simple phase control device? Maybe you
> have a failing DIAC/SIAC which can be past off as a diode? That 2.2 uf
> Cap at 400V, is leading me towards that direction. Since that is a
> common value for the trigger pulse on the gate which gets generated by
> the DIAC.
>
>
>
>
>


The overlay next to the zener says Z1 and I can read 5V1 on the body but not
anything else. Its a bit difficult to do "diode" checks because of the 47
and 100Rs around, but I suspect failed C-E of the transistor if anything.
But I will sketch out cct first tomorrow , rather than start replacing parts
on hunches.
Does not actually knock out fuses, mains transformer runs hot .


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