Philips 32PS55 S3231 Powers up, then shuts off 20 seconds later.
 

A friend of mine has a Philips 32PS55 S3231 TV made in October 2002. It powers up, gets a nice picture on the screen, then shuts itself off. What could cause this, and how do I fix it?

Does it use an LO1.1U chassis? If so, there is a kit from www.matelectronics.com that contains a HOT, two electrolytic caps, and two smaller transistors. Usually, the caps fail and will eventually take out the HOT. These parts are in the horizontal driver circuit.

The HOT's fine. It gets a nice picture, for the few seconds it's on.

I also remember a cap failure in a circa 2002 20" Philips that caused your problem. It was either a 47 uf or 100 uf, 200V cap in the B+ line.

All right. I'll start cap hunting tomorrow.

I don't think it's a bad cap this time.

I've tested all 160 volt and higher caps, and they've passed. Also, the caps are Nichicon caps, which I know to be a reputable brand.

Also, the TV's been doing this for at least 3 years, according to the owner. It's been sitting around since then and now he finally wants it fixed.

Something in the b+ gets overloaded? When the set turns off after the first initial 20 seconds, then power it back on. Does it take another 20 seconds to shut off again or is it much faster the 2nd or 3rd time around?

Call me dumb but I would resolder all heat syncs on the PCB. I have found this a time or two. Something is overheating shutting down the PS

I tried powering it up, letting it shut off, then powering it back up again. There was no decrease in the time it took to shut off.

I just had another thought. I've never experienced this on a Philips; but, I've heard that on newer Philips sets that the master G2 control (on flyback) must be set correctly or the TV will shutdown. I have experienced this on a newer RCA that I replaced the flyback in. It was a trial and error process; but, I finally got it adjusted where the set would stay on.

The VG2 control can be adjusted without having to take the case off. I doubt that's the issue.

On a hunch from a post on another forum, I started looking at the resistors on the CRT neck board. I found a 25-26 ohm resistor that reads only 1 to 4 ohms. When I can, I'll replace it and see what that accomplishes.

check all low voltage electrolytics in the PSU stage, especially the smoothing capacitors on the B+ rails, they may fail and overload the PSU or cause excessive switching ripple/insufficent voltage to reach the signal/logic circuits.

Are you testing that resistor with a leg pulled from the board?
I second that g2 control, seen it too, and especially since it's accessable from the back of the set, someone could have cranked it up. Sometimes it doesn't take much to run the PS into shutdown.

Removed it completely from the board and tested it three seperate times.


Also, if the VG2 control could cause this TV to shut down, then why is it accessable without even having to remove the back cover? Makes no sense if it could shut the TV down. Also, this TV's owner is very unlikely to even know what a VG control is, much less poke in a screwdriver to adjust it.

That's a good question; but, I know they can get turned, even if the owner does not realize it. I fixed a 36" RCA for someone I know and showed them how well it played before they left with it. They loaded it up, took it home, and called me complaining that the screen was almost black. I went over there the next day and both the focus and G2 controls were turned down. They swore that they didn't touch those controls and they had no idea how they got turned down. On this set, both controls could be turned with the fingers without removing the back.

It could also be that the CRT has gotten slightly weak, throwing off the original G2 adjustment.

""It could also be that the CRT has gotten slightly weak, throwing off the original G2 adjustment.""
i see it a lot in the philips chassis. their crt,s were not much better than zeniths. and the g2 setting will shut down the set. to low or to high and the damn thing will shut down. steve