[TechAssist] Re: Maganvox CM2015
- From: paul <ripajen@xxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Tue, 11 Dec 2001 11:37:07 -0800 (PST)
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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