Expert: cleggsan - 3/3/2010

Question
Our CS2725R TV (manufactured,'91) recently refused to power up and instead clicks off immediately with what appears to be the action of the power relay. I believe that is due to power supply drawing too much current as the result of a short of some sort. I've checked all the electrolytic capacitors that are shaded in the Sams folder and find no problems. I checked the resistance to ground of the 7 higher voltage sources (there are 28 lower voltage) put out by the power supply and find that only the 129v is suspect: it shows a resistance to ground of 2.6 ohms. 8 of the 129V attachment points have high resistor inputs, but three are connected to the pcc side transformer (T533), two of which are on either end of the primarly winding with an electrolytic in series on one of these, and third 129 input is to one end of the secondary with a 1 ohm resistor in series. The other end of the pcc secondary winding goes into pin 2 of the flyback transformer which of course is where the 29-33kV is generated (T532). In the absence of anything else to go on, would you believe that this indicates that the pin 2 of the flyback is shorted to ground and that is the cause of the refusal of the circuit to power up? Unfortunately I would have to remove the PCC to measure that, and I wouldn't know what to make of its reading but I would suspect it is near 0 ohms. No details are shown for the internals of the flyback but its part no. is 334P205070.
If that is not the likely cause, can you suggest another place in the circuit to look?
Thanks sos much for sharing your thoughts about this. I would like to keep this reliable set going longer.
Roland
PS I am an Allexpert participant in the category of Chrysler Repair.

Answer
First thought on my side is failure of one or two of the electrolytics.  You indicated they had been tested but unless they were tested under voltage stress the results may have been erroneous.  Most checkers do not apply enough voltage to break down the electrolyte insulation material.  So, my suggestion is to replace the lytics. It is not so expensive and maybe just the main ones in the ripple filter will do the job.

When the dc lines are low it is almost always a sign of excessive drain somewhere and the lytic are the first culprit to suspect.  Further, the set is very old; another reason to suspect the lytics.

And, yes, the horizontal output section could be shorted down which would put drag on the DC line and would incapacitate the high voltage.  And, the flyback could be the cause of failure in the HOT.

Those are my thoughts.  Let me know if there is more to the story............