For those of you who own an older Dell plasma HDTV and your screen suddenly stopped working, you might want to read up on these instructions that show you how to diagnose and fix your HDTV. I am guessing this might be happening to a lot of other Dell plasma HDTVs but don’t try this unless you’ve got some knowledge about electronics and soldering stuff.
More testing in the lab revealed that the problem was a defective IC, U501 which is a Fairchild Semiconductor part KA3883. I ordered a replacement from digikey, 497-3678-ND , which is a STMicroelectronics UC2843B, for $1.09. The original KA3883 is not generally available(discontinued?). UC2843B is a higher quality drop-in replacement.
The proof that the current mode pwm control chip(KA3883) was the source of the problem came from heating just that part with a hot air pencil and watching the Va voltage go up to 60V then cooling the control chip(KA3883) with a can of compressed air and watching Va go back to zero. The part is defective and for whatever reason responds to thermal shock. This could have indicated a cold solder joint but, after checking, the solder joints looked fine. Diagnosis: defective KA3883.