NotTaR of Television Sets : Ken's comments on (TV) SMPS repair      
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Ken's comments on (TV) SMPS repair

(From Kenneth Aaron (kennetha@geocities.com).)

  1. NEVER NEVER NEVER power on a SMPS without load, the newer ones especially in TVs (not so much VCRs) self destruct when not loaded.

  2. The light bulb test is great to see if your SMPS can handle the load of the horizontal circuits - when the set does not turn on - you get the initial power on then it goes off - best is to disconnect the collector of the horizontal output transistor and plug in a light bulb and see if it goes on.

  3. Chinese TVs have poor quality capacitors - the latest models mostly have the same SMPS so this applies for all. There is a small electrolyte cap in the supply feedback about 22 to 47uF at 50V. This dries up real fast and after 2 years or so the voltage B+ goes up from 110 V to anything up to 300 V! (not joking here). I got a TV where the end of the tube was blown off from a supply that reached 296 V instead of 105 V. that's over 75kV into the screen!

  4. The newer Philips and copycat Chinese models use the main supply to power the horizontal. The flyback is driven by a transistor which has over 2500 V on it's collector. The flyback is built differently as well. These transistors are called 2DS... - do not use a replacement - I did use one with a higher voltage and it fried - this is because the ceramic capacitors around it along with it's different characteristics changed the 'on' time and it overheated after a few minutes.

  5. You can always use a BU208D instead of a BU208A, BU508D instead of BU508A, etc, the extra diode will do no harm.