[TechAssist] Re: Sylvania(Funai) WSSC192 combo..33v zener shorts
- From: "John at Main TV" <maintv2004@xxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Mon, 27 Sep 2004 11:18:46 -0600
That may be possible but the feedback voltage would be critical. I think a
much safer way was posted last week. It said to apply a variable voltage to
whichever source line supplied the feedback (with no power applied) and
monitor the primary side of the opto-isolator with an ohm meter. As the
external supply approachs the rated voltage you should see a dramatic change
in the resistance reading. John.
John Mielke
Main TV
636 main St.
Longmont, Co
phone 303 776 6955
fax 303 776 0792
maintv2004@xxxxxxxxxxx
----- Original Message -----
From: "Christopher Barnak" <cbarnak@xxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Monday, September 27, 2004 10:23 AM
Subject: [TechAssist] Re: Sylvania(Funai) WSSC192 combo..33v zener shorts
> 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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