[TechAssist] Re: Magnasonic TV (Emerson??) model GCT5536, darkpicture

Gary,
From Tech Repair CD, searching "all fields" for that IC by searching for 
!TA8680:
·TOSHIBA·CF917A·SNOWY NOISE OR WHITE SPOTS THROUGHOUT PICTURE MAY HEAR LOW·HISS
SOUND OR HAVE AUDIO SPIKE INTERFERENCE.···REPLACE IC501 NEW IMPROVED TYPE 
TA8680N
(PN: B0383100) THEN·BE SURE MAKE THE FOLLOWING ADJUSTMENTS: WHITE
BALANCE*·SUB-BRIGHT* AFT* CW SUB TINE & SUB COLOR & RF AGC·ADJUSTMENTS···

I know not exactly the same symptom, but maybe will lead you in the right
direction.

Jeff
FAX 717-564-4952
Intrepid Video & Electronics
501 Luther Rd
Harrisburg PA 17111-2055
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>
> > From: Gary McCartney <number63@xxxxxxxxxxxxx>
> > Reply-To: techassist@xxxxxxxxxxxxx
> > Date: Thu, 27 Jun 2002 01:23:21 -0400
> > To: techassist@xxxxxxxxxxxxx
> > Subject: [TechAssist] Magnasonic TV (Emerson??) model GCT5536, dark picture
> >
> >
> > This is a Magnasonic TV (Canadian no-name brand) model GCT5536. No FCC#,
> > made in 1992. It is a 19" set. I believe this chassis could possibly be
> > Emerson but not sure about that. It uses TA8680BN as the jungle chip and
> > a no-name Chinese picture tube (chungaua or similar name).
> >
> > I actually have two identical sets, one works fine. The other one has
> > dark picture (video can be seen but very dark). The problem is in the
> > front end video circuitry as opposed to the flyback screen adjustment.
> > I have been comparing voltages and waveforms with the set that is
> > running fine. No schematic but I do have a pinout sheet for a TA8680N
> > IC.
> >
> > The problem appears to be the video waveform on the TA8680BN, IC301 pin
> > 38 being too low. THe video signal going through the chip is at the same
> > level as the good set until the signal comes out the chip at pin 38. On
> > the good set, this waveform is 0.5V p-p with NTSC test pattern on
> > screen. The bad set shows approx. 0.20V p-p at pin 38. Good set measures
> > 3.4V dc at same pin and bad set measures 2.5V dc. If I take a low value
> > resistor and jump from pin 43 (where video enters chip) to pin 38, the
> > picture becomes somewhat brighter. Have checked for something loading
> > down pin 38 but no luck. This makes it appear as problem is the TA8680
> > chip, however I have replaced it with a used chip, then again with a
> > brand new chip. The measurements are the same with the new chip, however
> > the picture is slightly brighter.
> >
> > Why am I losing amplitude of the video signal inside the jungle chip? B+
> > to chip is bang-on 9.0V. Changing chip doesn't help and can't find
> > anything externally loading it down. I need to get the 0.20 V p-p signal
> > back up to 0.5V p-p as is the case with the good running set and then I
> > am confident that the screen will have plenty of brightness.
> >
> > Does anyone have a suggestion as to a model cross to Emerson or some
> > other brand or even have a schematic for this DOG?
> >
> > Thanks for any help.
> > --
> >
> >
> >
> > Gary McCartney
> >
> > McCartney Electronics
> > 7134 Fife Rd, RR 7
> > Guelph Ontario Canada N1H 6J4
> > Fax: (519)821-1530
> > email: number63 (at) inetsonic.com
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