Power ok but not eht function
If you have tested the secondary section of the SMPS power supply of your Sony TV, amd found it OK I thinks, and posts this solution.
If the secondary supply rail 125VDC is found ok, just goto to the Horizontal Output Transformer, a small transformer diretly soldered on tho the main board, very near to the Line Output Transformer [LOT], and its secondary winding is connected to the base of the line output transistor, which in turn drives the LOT said above, generates EHT you described.
The base of the line output transitor must get appropriate frequency to switch on and off. This frequenct is gerally comes to 15625Hz. Just measure the voltage across the primary winding of the above said line driver transformer, which can be a possiblity open winding. Check the voltage at the collector point of the line drive transitor connected ti the one end of the primary winding is easy. Then check the voltage at the other end of that winding. There must be a little difference of 2VDC or so, if the line drive section is working, and fault is after that section, that is line output section. If you have a digital multimeter capable of measuring frequency, measure the frequency of the collector point of line drive transtor, and find out whether there is 15625Hz or near to this frequency comming out. Never touch the multimeter prob to the collector of Horizontal Outout Transistor, while it is working. Your meter will get damaged.
Line output section, contains tha LOT said above and line output transitor. If the Line Output Transistor has some sort of leak, normally collector to base leak, it will not drive the LOT to produce EHT and it wlii heat up also.
Just check it heat effect, after switching the set on for a short period of time, say 30 seconds ro so. If it heats up abnormally, suspect the line output transistor and LOT. You just replace the line output transistor first, with same type and number. If it doesn't retify your problem, LOT said abve is faulty, and it also should be replaced with same type and number.
If you have to replace the horizontal output transistor, and the LOT said abve, insist on orginal, and not replace it with a susbstityution, as these are critical components in all TVs..
If you need further assistance, get me through Fixya, and be free to conact me. Ok
Nov 29, 2010 |
Sony KV-XA21M61 21" TV