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Testing Power Supply in TV

 
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peterk



Joined: 10 Jul 2004
Posts: 17
Location: sydney, australia

PostPosted: Sun Apr 01, 2007 2:01 am    Post subject: Testing Power Supply in TV Reply with quote

Teac CTV CT-M6845 doesn't start, no B+, no smaller voltages. I have put a lamp on the B+ rail before the LOPT. I have tested each component individually in the Primary cct. There is no SMPS, just 3 trans., 3 diodes in series, a few res., and some ceramic caps. There are no electrolytic caps in it either. ACvolts are present.

Protection is via feedback from the Secondary output to an OptoCoupler whose o/p then connects to one of the smaller trans. (across B-C pnp).

Anyone have suggestions on how I can test the PS please. Can I override the optocoupler. Obviously, I assume, that the Primary cct has to start oscillating somehow but this I can't figure out.
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tv.service



Joined: 30 Mar 2007
Posts: 19
Location: Sweden

PostPosted: Wed Apr 04, 2007 6:39 am    Post subject: Reply with quote

First check if you have about 300v on the drain of the switching FET transistor.
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PostPosted: Fri Apr 06, 2007 12:11 am    Post subject: Reply with quote

Yes there is, btw, it is a trans (collector), passive measurements test each component ok, dc volts drop are across all silicon devices, pulses do not start.
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tv.service



Joined: 30 Mar 2007
Posts: 19
Location: Sweden

PostPosted: Fri Apr 06, 2007 1:33 pm    Post subject: Reply with quote

You must check if you have 300v at the collector. Also check if you have the right voltage at the base of the transistor and check if you have the start-up voltage somewhere in the circuit. This voltage is usually 12 or 18v.
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