Vestel 11AK19 power supply problem

[torbjorn]

A tv with this ill-fated chassis (28", 4:3, 110° crt) was completely dead at first instance. After replacing two diodes in the mains rectifier bridge and R817, the power supply starts but is tripping. I have tried disconnecting all loads (removed L802, D812-D815, IC804) and loading the +150V line with a 2,2 kohm resistor (also tried a 230 V 40 W lamp with similar results). However, the PSU is still tripping. After switching on, it supplies almost exactly 150 V for about 0,15 seconds, then the voltage drops to about ten volts and the PSU begins tripping.
So, the voltage control circuitry seems to operate correctly. Also, i have checked C829 (filter cap for +150V) and R819 (source resistor for PSU switch transistor) and they are ok.

Any suggestions?

[vtech]

Not familiar with the set but took a look at a similiar one here;
http://www.eserviceinfo.com/downloadsm/20771/FIRSTLINE_11AK19.html

Some things to check w/ smps

Can you bring it up slowly on a variac and do some monitoring? How does the feedback line level look and is it changing?(starting from cathode of D811 going back thru opto)

See if you can monitor around IC801/802 to see if it shutting down for no reason or being triggered & ofcourse dried 'lytics are always suspect. ...do not see a need for loading the 150V line in this case.

[mickeymay]

I know this sounds strange, but have you tried replacing the LOP tranny by a known good one, sometimes they can become faulty (especially on this chassis) without any kind of abnormal meter reading.

[torbjorn]

I don't think so in this case, as i have tried disconnecting the supply to the line output stage and loading the power supply with a lamp.
For the moment, that television is put out in a shed, waiting for better days and new clues...