50PF9830a/37 Philips Plasma Power Supply Issue

[ghiotom]

Recently, after the power flickered on and off, I've had a problem where the tv will cut off and flash the red LED one long and four short. Sometimes the tv will be on for hours before it goes into protection, sometimes as little as 10 minutes. I think the code refers to the audio, which has 18v and -18v power, This is what I get when I hook up the scope to the 18v line. The caps check good on the ESR meter. I'm not sure I'm measuring properly because that seems like a lot of noise. Any ideas where this is coming from?

[tom66]

Re: 50PF9830a/37 Philips Plasma Power Supply Issue

Where is your ground? You should measure across the +ve and -ve of the cap, or as close as possible.

Try turning on bandwidth limit - 20 MHz limit.

[ghiotom]

Re: 50PF9830a/37 Philips Plasma Power Supply Issue

I'm using the chassis ground. Other voltages look good with the same settings.I don't want to move the ground probe, won't that cause problems with voltage potential between points?

[tom66]

Re: 50PF9830a/37 Philips Plasma Power Supply Issue

You need to probe against the ground of the cap as the chassis has serious currents behind it from the plasma display. Fine for measuring DC voltage, but if you try and scope it, you'll just pick up a lot of noise.

An alternative is a ground directly on the PSU itself, very close to your test point, but the best is straight on the negative of the cap.