"news.rcn.com" wrote in message
...
This is an Insignia Model: IS-HTIB102732 progressive scan home theatre DVD
receiver. It was accidentally plugged it into a 220 volt source and
"clouds" of white smoke apparently started coming out of the left hand
side where the power supply is, even though the person who did it says it
wasn't actually turned on. (surely if it was unplugged, plugging it in
would put it into stand-by mode, - it wouldnt try to turn itself ON?)

The wall fuse blew about five seconds after it started smoking.

The unit does however now turn on! And it seems to work. And I cant see
any damage to the power supply area on the left of the unit! Curiously
there is what looks like a fuse on the power supply board which doesn't
even look blown?

The problems for which it has come to me are that it seems to have lost
dynamic range (though I have no way of knowing what dynamic range it had
before it started smoking), the left front channel power seems very low
and the DVD displays for a few minutes then the picture gets very choppy.

Does anyone know if any of this can be traced to whatever is powered when
the unit is in standby mode? Logic seems to dictate that the only thing
needed to be powered wjem in standby mode is the remote unit and that
seems to be working.

I have difficulty in believing that the left hand power transistors or the
servos to the DVD laser were powered when the smoke incident took place.

It does tout itself as a 1000 watt unit which seems to me more than a bit
like a very 1960s looking figure. The speakers are incredibly tinny
looking and the sub is made predominantly of particle board. The unit has
no weight to speak of to support any sort of power transformers supplying
1000 watt transistors and heat sinking to them looks minimal. I suspect
the impedance is under an Ohm (and I have it connected to ordinary 8 ohm
speakers at the front)

(Yes, it IS made in China)


The first thing to note is that any output power quoted on these Chinese HC
and hifi systems, is a total power, so with 6 channels of output, that takes
it down to 180 watts per channel before you start. The next thing to note is
that the power quoted is
back-pedalling-mid-winter-differential-peak-garage-music-with-a-following-wind
power, which is aproximately 50 times RMS output power, so 3.6 watts RMS
into 4 ohms per channel, is about what you can expect to get ...

As far as what exactly was powered when the excess voltage was applied, you
can by no means assume that it was only the standby supply. Many such items
will come fully or briefly fully to life, after power is reaplied from a
full power down. This allows the system control micro to do a status check
on the machine's current mechanical condition, and also allows the system to
check for such things as pending timer events, or to resume playing and so
on, after a power interuption, which may be due to an external power line
interuption, outside the user's control. Many units 'remember' whether they
were on, before the power was removed, for just this reason.

Further, if a switcher is hit with double the voltage it's expecting, then
after being very lucky that the side of the chopper transistor didn't zoom
off into space, there's no telling what unpredictable things that the power
supply may have done as a result.

There are not too many places that a "cloud of white smoke" can have come
from, without any obvious damage being visible. My best bet would be that it
came from the main filter cap. If the power supply is designed for 110v
operation, then the chances are that this cap is rated to only about 200v.
If 220v ac was applied to the unit, the voltage across this cap will have
been in excess of 300v. Release of the magic white smoke is the usual result
of doing this to an electrolytic.

Without any further messing about, the very first thing that I would do, is
to replace that cap. It could well be damaged, and be causing the supply to
suffer excess primary-side ripple. This in turn, can lead to erratic
operation, and excessive noise on the secondary rails, which may well result
in poor playability issues. I do, however, feel that lack of output on one
front channel compared to the other, is unlikely to be a power supply issue.
I would feel inclined to investigate this by putting a CD test disc with
audio tones on it, into the machine, and then comparing levels between
channels, with a 'scope. Is the value of the unit sufficient to warrant your
time getting into this to component level, though ... ?

Arfa