[TechAssist] Re: Sylvania(Funai) WSSC192 combo..33v zener shorts
- From: "Jerome Silverman" <greentron@xxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Mon, 27 Sep 2004 20:50:51 -0400
The problem is that the feedback system is high gain in order to regulate
closely. So if you are subbing a resistor for the opto, when you reach the
critical value the output goes from full off to full on (or vice versa)
thereby damaging all the stuff that the protective devices are supposed to
protect. You could probably devise some sort of system to protect the loads
in troubleshooting but you would have to work it out for each different
supply.
If the output voltages are too high and there is no more damage to be done,
you can short the phototransistor output of the opto and the SMPS will shut
down if the primary components are working.
Jerry Silverman
Greentron Inc
4 Newland Ave Greenville SC 29609
Fax/Phone 864 232 3889
greentron@xxxxxxx
----- Original Message -----
From: "Christopher Barnak" <cbarnak@xxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Monday, September 27, 2004 12:23 PM
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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