[TechAssist] Re: Magnasonic TV (Emerson??) model GCT5536, darkpicture
- From: Ed Gaidies <teltek2@xxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Thu, 27 Jun 2002 08:15:58 -0400
Gary;
The older Toshibas use that chip. I will look thru my schematics, seems to
me with Toshiba it was a couple .01 disc capacitors, not sure which ones,
though.
- Ed -
TEL-TEK ELECTRONICS
Ontario-Canada
"Quality will be remembered....long after Price is forgotten"
teltek2@xxxxxxxxxxxx
teltek1@xxxxxxx
> 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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