Riddled TV Repair Forum

abstract · Joined: 26 May 2010 Posts: 4

Panasonic 36" CRT, CT-36SX31E, chassis BP372

Lately this problem has been getting worse. A few weeks ago, it started to take a few seconds longer for the picture to appear when the unit was switched on.

Now, it takes about 45 seconds for the picture just to start to appear, and at least 5 minutes for it to fully fade-in. This happens regardless of the input, and affects the on screen menu as well. The picture is also now noticeably darker and oversaturated, something I can't seem to fix with the brightness and picture controls. There is also a 1" black gap at the top of the screen; the image seems to have shifted a few inches downward as network logos are now cut off.

This is what happens when the unit is turned on after at least 30 minutes of being off:

1) nothing for the first 45 seconds
2) black and white image appears for a few seconds, taking up the lower half of the screen
3) image slowly stretches upwards, color appears
4) image is fully "stretched", but with a 1" gap at the top of the screen, image appears to be offset 2-3" lower

If I switch the unit off after it has "warmed up" the image appears immediately when I turn it on again.

I'm fully prepared to open this baby up as I've grown quite fond of it over the last 7 years. I do have the service manual but would appreciate tips of where to start looking. I'm hoping for something immediately obvious like a bulging capacitor or burnt part but I doubt I'd be so lucky.

Thanks

Google

kuhurdler · Joined: 28 Dec 2006 Posts: 2571 Location: Overland Park, KS

check the vertical circuit:
IC
caps

JTS1957 · Joined: 21 Jan 2009 Posts: 1331 Location: Far, Far Away

Try: C832 220ufd 16volt

abstract · Joined: 26 May 2010 Posts: 4

Ok, finally got the unit open. C832 looks ok; I do have another cap that I am prepared to solder in once I disconnect all the cables.

Question - can I unplug the flyback cables without discharging the tube? And all the other cables hooked into the PCB for that matter? This is the first time I've attempted a TV repair other than replacing a fuse.

JTS1957 · Joined: 21 Jan 2009 Posts: 1331 Location: Far, Far Away

IF "looks good" were nickels, I'd be very rich. Let's try a "meter" of some sort, rather than your eyes.

I'd get a bigger workbench and leave as much plugged in as possible. You're only asking for trouble trying to disconnect things you may not know how to safely disconnect.

Google

abstract · Joined: 26 May 2010 Posts: 4

Ha, true enough. I was half expecting a smoldering burnt part that would be crying out for replacement, but no such luck.

Ok, I figured out how to pull out and tilt the board trays so that I didn't have to unplug much (I discharged the tube and checked the cap voltages just in case).

My DMM isn't telling me much about the C832 except that it's not shorted. I have an LCR meter at work that will give me an actual value, but if I'll be desoldering the cap anyhow I might as well replace it.

Looking at the schematic C832 is a part of the circuit that feeds unregulated 11V into the 5V regulator IC881 on the A-board. Are you thinking the 5V line is bad?

JTS1957 · Joined: 21 Jan 2009 Posts: 1331 Location: Far, Far Away

IF unregulated 11 volts is lower than normal, regulated 5 volts may also be lower than normal.
Note that you didn't report any voltage measurement.

abstract · Joined: 26 May 2010 Posts: 4

JTS1957, you were spot on. C832 measured to be very low, around 100 uF or so. I replaced it, checked the unregulated 11v and regulated 5v lines and everything was ok. The set is back to it's normal self again.

Thanks!