[TechAssist] Re: MAG: 25X6 chassis Quick Question?
- From: "Electric Medic" <info@xxxxxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Sun, 20 Jan 2002 09:12:12 -0500
Friends:
We used to use the light bulb test on Motorola base stations to find shorts
after lightning strikes. If the bulb had a bright glow, you had shorts to
find. We just simply repaired circuits until the bulb went dim. But those
had a round screw in fuse the same size as a light bulb. We have found on
most TV's, if you run your powerite down to around 80 volts, you may not
blow any parts if the flyback is bad, however, the flyback will get warm, or
in some cases might even smoke a little. The best way though is to use a
Sencore VG92, and do a load test, with everything in circuit. It will check
your timing and loads, you will know in less than five minutes if your
flyback is bad. That is just what works for us. It is hard to get my young
techs to solder a light bulb socket into a little TV chassis. They try to
come up with quicker test. My 2 cents.
Perry Bower
Electric Medic
"It's Cheaper to Keep Her"
3850 Washington Road Suite 5b
Martinez, Georgia 30907
Phone: 706-8MEDIC4 (863-3424)
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-----Original Message-----
From: techassist-bounce@xxxxxxxxxxxxx
[mailto:techassist-bounce@xxxxxxxxxxxxx]On Behalf Of Dennis Viereck
Sent: Sunday, January 20, 2002 2:22 AM
To: techassist@xxxxxxxxxxxxx
Subject: [TechAssist] Re: MAG: 25X6 chassis Quick Question?
No need to blow up any parts. Use a 40 watt light bulb in series with the B+
to
the flyback. Connect your oscilloscope to the collector of the horizontal
output
transistor. Set the scope to resolve a 600 volt PP signal at 10 micro
seconds
per division. Power up the set an look for a clean undistorted pulse with a
duty
cycle of 11.7 microseconds "OFF" time and a "ON" time of 51.7 microseconds.
Any extra ringing or distortion means you have a heavy load on the secondary
or
an internal shorted winding.
The light bulb saves components, and buys time to measure the "Must Haves"
in
that circuit. Sometimes only 2 or 3 seconds is necessary to make this
measurement. Most of the time after a short test like this and it is a
flyback,
one can feel the heat generated in the flyback by the bad winding or diode
stack.
Dennis Viereck
Bill McFarland wrote:
> Hey no problem,
>
> The old "N" chassis used to do this all the time (The flyback was almost
> always bad)
>
> I was just wondering if anyone could say "Yea those crap the bed all the
> time!" It would give me a little more to go on when on Monday I use my
> "Stone-aged" BK 1077 to ring it. (Its only about 75% effective...And that
> only if the flyback is completely out of the unit)
>
> I hate blowing parts up!
>
> Funny thing is now that "I" am the one paying for the parts. I sure am a
lot
> more careful about things like this. When I worked for someone else it was
> faster to just change the HOT and Reg. and see if it blows the HOT back
up!
> (I was young...What can I say)
>
> Good luck, God Bless
> Bill McFarland
> DMC Electronics
> Salt Lake City, Utah
>
> ----- Original Message -----
> From: Dennis Viereck <wa6ati@xxxxxxxxxxxxxx>
> To: <techassist@xxxxxxxxxxxxx>
> Sent: Saturday, January 19, 2002 8:37 PM
> Subject: [TechAssist] Re: MAG: 25X6 chassis Quick Question?
>
> >
> > Opps... I can't read.... Never mind. You might be right......
> > Dennis Viereck
> >
> > Dennis Viereck wrote:
> >
> > > Depending on how the STR is shorted, I would the think the set would
> still
> > > run. Assuming the AC line voltage is reduced enough to achieve 130VDC
at
> the
> > > output of the regulator. This is a simple linear regulator and easily
> > > bypassed.
> > >
> > > A "Shorted" STR certainly would not point me in he direction of the
> flyback.
> > > Maybe if you had a shorted horizontal output transistor, I might feel
> > > inclined to agree with you. But certainly not on 1 shorted part and
> > > intestinal feelings......
> > >
> > > Dennis Viereck
> > >
> > > Bill McFarland wrote:
> > >
> > > > Hello all,
> > > >
> > > > I am working on a 25X6 Maggot-box.
> > > >
> > > > Shorted HOT, Bad STR30130 Regulator.
> > > >
> > > > My gut tells me the flyback is probably bad as well.
> > > >
> > > > Can anyone tell me if the Flyback is a common failure item in this
> unit?
> > > >
> > > > Good luck, God Bless
> > > > Bill McFarland
> > > > DMC Electronics
> > > > Salt Lake City, Utah
> > > >
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