Convergence amp replacement - thermal pad or thermal grease?

**boredwild** · **09-12-09, 05:58 AM**

Convergence problem on SP43W6HF rear projection TV: In replacing the STK392-040 ICs, should I re-use the thermal pad which resides between these devices and the heat sink, or should I use a thermal compound/grease instead? So far I have replaced 4 burnt resistors in the blue and green amplifier sections, and I am waiting for the new STKs to arrive. Wish me luck.

**lcaillo** · **09-12-09, 12:26 PM**

I always use the pads. More of the problem with overheating in the samsungs seems to be excessive d.c. offset into the ICs and excessive edge correction. Some techs use fans, some use paste, but I never do either, just set them up carefully. It takes much more time, attention to detail, and skill, but I never have repeat failures on them.

**boredwild** · **09-13-09, 11:11 PM**

Thanks for your quick reply. I really appreciate the help that you so freely provide here. What do you think would be the cause of excessive DC offset? Aging components? Just check Vcc + and - for these amps? Also, what is meant by edge overcorrection? Any advice on how to set up carefully? Perhaps I should just relax until I get the new ICs, but the 21" Sony is just not cutting it!

**lcaillo** · **09-14-09, 07:18 AM**

They come from the factory set up very poorly. Lousy quality control, disconnects between engineering and production, lack of understanding of effects of engineering decisions on field repairs, etc are all reasons that this is the case.

Read the first ten posts of the convergence repair thread. This is discussed in detail.

You have excessive correction when you get diminishing effects as you drive the chips harder. It usually occurs at the edges and may start with poor setup in nearer the middle. You may need to trade off geometry or edge convergence. Sloppy design and limitations in the yoke/crt combination are the reasons. These are cheap sets that never were that great to begin with, and even with very skilled alignment are mediocre at best.

These sets can be a challenge for even a very experienced tech, so don't expect too much.

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