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ELBE E-15 tv with vertical/frame squeezing in

I'm currently trying to fix this ELBE 14" TV, chassis E15. On power up, all appears well, but after about a minute (less on subsequent switch-ons) the frame begins to twitch, then (relatively) slowly squeezes in to the familiar horizontal line.

see extract from schematic here:

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I have already changed most the capacitors including the 50v decoupler and the 10uF on the supply/feed. No change. the supply voltage seemd OK measured warm, but will measure this again from cold. This fault seems odd to me, as usually in such cases there is either no frame at all (open resistors, bad frame chip, broken connection, etc) or a reduced image/foldover on power up (bad capacitors hi res resistors, etc) which often improves with warmup. This, however, appears to be the reverse. Any ideas before I change the two o/p transistors?

TIA

-B

Reply to
b
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It sounds like the frame IC overheating, check that it is properly attached to its heat sink, could also be due to some overload or overvoltage. Many ICs have a temperature protection that limits the output current if its internal die gets too hot. I once had this in a Philips set and had to replace the frame IC, either it was oversensing the temperature or its internal die fell off from its metal pad.

Reply to
Jeroni Paul

thanks, will follow that idea! B

Reply to
b

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