Philips MD2.22 chassie

[vtech]

Counterfeit semiconductors are indeed a major problem and some are rather hard to detect. (one reason I do my best to nuke any "Chinese" ad here). Of course the best weapon is to try to stick with known supplier(s). Another way is to compare the logo on the device. On many occasions it is a dead giveaway. Here is a logo source
http://freespace.virgin.net/matt.waite/resource/logos/index.htm.

Test equipment such as a curve tracer can be used to look at the performance signature but surely not too practical when trying to repair something.
Also, here is some good information
http://sound.westhost.com/counterfeit.htm
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[netblues]

Back here again..

The bu and fet change worked well and the set is stable since repair.
However lately I hear 50Hz interference from speakers, the more intense and white the screen is, the more 50Hz I hear.

I know it must be some capacitor somewhere dried-out..
Question is WHERE?

[torbjorn]

Check whether the 50 Hz interference is syncronous to the mains or to the video signal, that will give a clue of where to look for the problem.

A method of checking it is to connect an oscilloscope to the loudspeaker output and adjust it so you see the interference. Then try trigger the scope from the mains or from the video signal and see when the interference gets stationary.

If the problem really is due to crosstalk from the video signal to the sound circuitry, double check that all ground connections from the CRT board, CRT coating etc are correctly fitted, and also check that no CRT related cabling is located near sound related cabling in the set.