[TechAssist] Re: [Fwd: RCA CTC169BG 35 inch. sound modulates the video]

Believe it or not,my tech friend was looking at the +24/+17V source
derived from a common Diode CR4119 cathode. There was a capacitor,
C4147, a 680 mfd@ 50v filtering it. (one of three larger caps just in
front of the SMPS transformer)As a hunch I pulled and replaced the cap.
The TV has been OK ever since. I ESR'd and cap measured the cap and all
tests were OK on it. Thinking back,I seem to remember one lead loose,tho
I may have wicked it earlier(I get many interruptions and go back a
dozen times so I lose my place some)Either it's highly intermittant,was
bad solder I reflowed, or this cap was really bad. It's been several
days now OK.Thanks.

Damon wrote:
> 
> Phil,
> I know this is unlikely to occur and I doubt this is what you'll find.
> However we had a Toshiba 35 inch TV with audio affecting the horizontal
> lines, turns out the speaker wire was pinched underneath the crt's metal
> mounting bracket. When we turned up the sound the pix would look like we had
> erratic horiz sync.
> 
> Looking at schematics: Block diagram shows Video/Audio is common to pin 45
> of U1001, passes thru Q2302 buffer which then splits the audio thru cf1201
> 4.5 mhz bpf to pin 51-u1001 input to fm detector which outputs to pin 57.
> Video from q2302 goes thru cf2301 4.5 mhz trap filter to q2701 buffer. This
> same video is used on big pix and pip pix, so you may want to see if pip pix
> is also affected. BTW does it shift the horiz,. or does it brighten/darken
> the video?
> 
> Let's see if there are common power supplies: Well....yes and no. Looks like
> the major power supplies are a + and - 12 volt supply which is broken down
> to 5 and 6 volts on the audio process (stand up board) board, your -12 volt
> line comes from the ihvt and CR4705. Your +12 comes from Q4702 (12 v Run
> switch). That's it for audio and about the only 2 supplies you need to check
> for audio noise. The + 12 volt is the only true common power supply, maybe
> you should check the pinched wire as a likely possibility.
> 
> Hope this helps.
> Damon Brunger
> damon101@xxxxxxxxxxxxxx
> Telrad Electronic Services
> Ft Wayne, IN 46815
> ----- Original Message -----
> From: "Phil Bader" <philbad@xxxxxxxxxx>
> To: <techassist@xxxxxxxxxxxxx>
> Sent: Tuesday, January 29, 2002 1:18 PM
> Subject: [TechAssist] [Fwd: RCA CTC169BG 35 inch. sound modulates the video]
> 
> >
> >
> >
> > -------- Original Message --------
> > Subject: RCA CTC169BG 35 inch. sound modulates the video
> > Date: Tue, 29 Jan 2002 13:17:20 -0500
> > From: Phil Bader <philbad@xxxxxxxxxx>
> > Organization: Jan Phyl TV Inc. Winter Haven, Fl.  Est.1976.vioce/fax
> > 863-299-8821
> >
> >
> > At low volume levels the pix is very good.Turn up the sound and the
> > picture modulates at the audio rate.I assume there may be a common
> > video/audio voltage source that is sagging under load. Any
> > histories?-Phil
> > ------------------------------------------
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