[TechAssist] Re: Sylvania(Funai) WSSC192 combo..33v zener shorts
- From: "Christopher Barnak" <cbarnak@xxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Mon, 27 Sep 2004 12:23:48 -0400
Jerry,
Have you (or anyone out there) tried controlling the switching of the
SMPS Regulator
by injecting voltage or varying resistance on the primary side of the
Opto- Isolator ??
I've been successful in using your method. Also using a variac on the
A.C., but some
SMPS will just cut full-on even with very low A.C. input. Seems to me
the Opto could be
removed and a Pot and/or power supply across the opto primary points
could be use to regulate the supply so you
could troubleshoot the feedback path and find out why the thing won't
regulate.
Christopher Barnak, CET
Norfolk Public Schools
School Plant Facilities
966 Bellmore Ave.
Norfolk, Va. 23504
Phone 757 628 3385
Fax 757 628 3392
cbarnak@xxxxxxxxxxxxx
>>> greentron@xxxxxxx 9/25/2004 1:58:26 AM >>>
The zener is an overvoltage protector. The SMPS is not regulating so
the
output voltage is going too high and the zener is just doing its job.
Usually a tough one like this turns out to be a resistor, diode,
transistor, or some other part that is not easily tested in circuit.
Sometimes I have to figure out if the feedback problem is in the
primary or
secondary. The easiest way to do this is with an adjustable bench DC
supply
and an ohm meter. I hook the ohm meter across the optoisolator on the
primary side and apply an adjustable DC voltage to the secondary DC
output
line that operates the feedback. When the DC voltage goes above the
point
where the output line is supposed to regulate, the ohm meter should
show
that the opto phototransistor is drawing some current. If it does
this, the
problem is with the primary feedback components. If it does not do
this, the
problem is in the secondary feedback components.
Jerry Silverman
Greentron Inc
4 Newland Ave Greenville SC 29609
Fax/Phone 864 232 3889
greentron@xxxxxxx
----- Original Message -----
From: "Gary McCartney" <gary@xxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Saturday, September 25, 2004 1:21 AM
Subject: [TechAssist] Re: Sylvania(Funai) WSSC192 combo..33v zener
shorts
> Jeff, what about something unusual such as leakage between primary
and
> secondary of the SMPS transformer? Does the 33V zener blow instantly
or
> is there enough time to do measurements? Is the 33V rectifier
> installed backwards by any chance?
>
>
>
>
> Gary McCartney
>
> McCartney Electronics
> Guelph Ontario Canada
> Est. 1984
> email: gary (at) number63.ca
>
>
>
>
>
>
>
>
> Intrepid Video Support wrote:
> > Thanks Peggs...
> > I checked continuity on all the traces and pulled back the
coating..all
is fine in that area.
> > Jeff
> > --
> > Intrepid Video TV/VCR Repair
> > 263 S Front St, Steelton PA 17113
> > 717-939-7708; (F) 717-564-4952
> > www.intrepid-video.com www.tech-repair.net
> > ----- Original Message -----
> > From: "peggs" <peggs@xxxxxxxxxxxxx>
> > To: <techassist@xxxxxxxxxxxxx>; "Techassist"
<techassist@xxxxxxxxxxxxx>
> > Sent: Wednesday, September 22, 2004 11:36 AM
> > Subject: [TechAssist] Re: Sylvania(Funai) WSSC192 combo..33v zener
shorts
> >
> >
> > If there is a mounting screw near the opto,check the pcb for a
crack at
the
> > screw.
> > capstan motor are bad in many of these as well,it pulls the 12v
supply
down
> >
> > Peggs
> >
> > At 06:27 PM 9/21/04, Intrepid Video Support wrote:
> >
> >
> >
> >>Set came in dead, with a squeal.
> >>Replaced D615(33v), Q605, Q606(Shorted) R566, high in value, D629
> >>(1N4148..shorted) and I replaced the
> >>opto..all diodes and transistors shorted again.
> >>I replaced again, this time replacing Q604..33v zener shorted
again.
> >>I checked D621, D609, D616, 617, 613, the 10 ohm resistor R654.
> >>Evidently I'm missing something..and losing on a job that should
have
been
> >>a quick fix..
> >>Can anyone offer any help?
> >>Thanks.
> >>Jeff
> >>--
> >>Intrepid Video TV/VCR Repair
> >>263 S Front St, Steelton PA 17113
> >>717-939-7708; (F) 717-564-4952
> >>www.intrepid-video.com www.tech-repair.net
> >>
>
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