[TechAssist] Re: Maganvox CM2015
- From: paul <ripajen@xxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Tue, 11 Dec 2001 12:05:14 -0800 (PST)
Bruce
Just another thought are all the parts in the driver
circuit OK ? Regarding the Line Output T/sistor is it
the original type and part no ? It may of had the
wrong one fitted in the past.
If wrong LOPTransistor used the gain will be wrong
causing all sorts of problems.
Paul
>
> Bruce
> Just a idea usually if you cant find whats wrong
> you
> have got to think what you have done. This applies
> with most things. ie replaced LOPTransformer etc. I
> wonder is the LOPT the correct one. Has the wrong
> one
> been given although the voltage is excessesivly
> high.
> Any chance of a wrong labeling on LOPT? OK on the
> Caps. Any chance of trying a extra Cap across the
> Original Tuning Cap to see if this reduces the EHT.
> No chance of a cracked core on LOPT?
> Paul
> --- Bruce Youmans <youmans@xxxxxxxx> wrote:
> >
> > Paul,
> > I haven't changed them but have tested tuning
> > capacitors
> > 2614, 2615, 2627, 2616, 2617, and diodes 6613.
> 6614.
> >
> > All test good. Any other components that you think
>
> > I may have over looked?
> >
> > Thanks for your help.
> > Bruce
> > ----- Original Message -----
> > From: paul <ripajen@xxxxxxxxx>
> > To: <techassist@xxxxxxxxxxxxx>
> > Sent: Monday, December 10, 2001 12:48 PM
> > Subject: [TechAssist] Re: Maganvox CM2015
> >
> >
> > >
> > > Have you tried checking the Flyback tuning
> > Capacitor
> > > or other components in this area?
> > > --- Bruce Youmans <youmans@xxxxxxxx> wrote:
> > > > Brand: Magnavox Enhanced VGA Monitor
> > > >
> > > > Model: CM2015
> > > >
> > > > Chassis: CM0200
> > > >
> > > > FCC ID: A3KM050
> > > >
> > > > Similar to some: HP, AT&T, Compaq, Apple
> > monitors
> > > >
> > > > Symptom: Dead. High Voltage transformer was
> > shorted.
> > > > Primary winding, B+ side, to ground. Usually a
> > sign
> > > > a voltage was too high and the transformer
> > shorted.
> > > > Horizontal output transistor was ok as well as
> > all
> > > > other critical parts.
> > > >
> > > > Transformer was replaced with manufacturers
> > > > original. Set now shuts down. Forced to
> operate
> > by
> > > > disabling the high voltage shutdown circuit.
> > High
> > > > voltage measures 32KV, should be 24KV. Checked
> > > > safety capacitors, damper diodes and all seem
> to
> > be
> > > > fine. MOSFET Q7916 does not seem to have the
> > correct
> > > > voltages on it. Drain measures +95 volts,
> should
> > be
> > > > +185 volts. Power supply seems to be operating
> > fine.
> > > > Have checked critical capacitors in the power
> > supply
> > > > circuit. Tried new MOSFET. I suspect the
> MOSFET
> > > > drive circuitry. I believe the MOSFET drive
> > > > circuitry is not driving the MOSFET
> sufficiently
> > and
> > > > the MOSFET is conducting more than it should
> > thus
> > > > loading down the +185 volt supply. In turn
> > causing
> > > > too high of source voltage which goes to the
> > high
> > > > voltage transformer causing the high voltage
> to
> > be
> > > > too high. Have checked components in the
> MOSFET
> > > > drive circuitry and they seem to be fine. The
> > pulse
> > > > on the primary of transformer, 5802, in the
> > MOSFET
> > > > drive circuitry looks good. The pulse on the
> > > > secondary looks poor, low level with a large
> DC
> > > > offset.
> > > >
> > > > Lost for additional things to try. Any help
> > would be
> > > > appreciated. Thanks in advance.
> > > >
> > > > Bruce
> > > >
> > > > Bruce's TV Service
> > > >
> > > > Sierra Vista, Arizona
> > > >
> > > >
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