Tip & How-To about Sony STR-DE915

No sound out of front and surround speakers but center works

Replace transistors Q703 and Q503
Sony P/N 8-729-422-57
Transitor P/N UN4111

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Sony srt 750p transitor problem


Transistor Problem


To replace the power transistors ( MN2488 and MP1620 )

• you need to have a technique in soldering.

( much faster is cut the transistors pins , but be careful only for

professional serviceman )


click on the link below:


Soldering Guide

After taking out the burnt transistors:

• get a multimeter and measure the DC voltages present on

each amplifier output stage ( center of the two resistors in series ).

• • it should be no more than 0.7 V, if it s, remove those pair of power

transistors and test again for output voltages.


the negative probe

of the multimeter to the chassis of the unit.


• Do not connect new power transistors yet.

you may need to power it without it.


Until you sure that the unit powers up and have some/other channel

working to prevent further transistors and components failure.





But if there are still more than 0.7 v on some of the outputs


• Check for VAS circuits and Differential Input Stages



Let me know how you make out with the inspection.

It is a good chance you will find something.


hope this helps, thanks for using Fixya!

Aug 09, 2012 | Sony Audio Players & Recorders

1 Answer

power ok but not eht function


Hello

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

2 Answers

when i put my tv sony trinitron on, i hear the sound for 15sec en then the tv go out en de leds blanks


Hello
There is some sort of indirect short inside your TV. It is in the main circuit board. Most of this kind of fault in Sony Tvs are related with horizontal output stage. You just replace the horizontal output transitor [which drives the Line Output Transformer] of your TV first. If the transitor is leaky, the above said falult may occur. If it doesn't help Line Output Trnasformer [LOT] may need replacement. Check whether the replaced transistor overheats within seconds or minutes. If it overheats the LOT is faulty. Ok.

Oct 18, 2010 | Sony FD Trinitron WEGA KD-36FS130 36" TV

1 Answer

no rear sound in surround


I replaced Transistors Q701 and Q703 on the rear amp board to fix dead rear and "B" speakers.

Jan 01, 2008 | Sony STR-DE915

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