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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gigabyte motherboard l1117 transitor heating & no power


You may have tor replace the motherboard - or take to an electronics shop to see if the transistor can be replaced - note: there may be other damage to the board itself, not just the one transistor.

Apr 11, 2014 | Gigabyte GA-G31M-ES2L Motherboard

1 Answer

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

1 Answer

no power ticking sound when plug into outlet


Hello

Your Philips Tvs line output section has some trouble with it. All philips power supply circuits are so designed that, even a small short circuit in the ciruit board occurs, the power regulator will sense it, and the entire system will shut down, and that is happening now in your TV.

You just start with the horizontal output transistor, fitted very close to Line Output Transformer [LOT], for any short. You must desolder it out from the circuit for this check, and check it for collector to emitter leak. If this will happen, the main regulated power supply ie 120VDC, will gets shorted through this transistor, cause a dead short circuit. If it is shorted, you must find out the reason for that short.

If LOT said above has damaged, this transitor will also get shorted. In otherwords, if LOT is damaged, its driver transitor,will also will get leaky. You just replace this transitor with an identical one. Switch on the tv for a while, say 10 seconds or so, check its heat effect. If it heats up abnormally, surely LOT has damaged, and you should replace it also with an identical type and number. Ok

Nov 24, 2010 | Philips 32PT563S 32" TV

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