Pioneer VSX-520-K Protection problem

[srt1]

Originally Posted by rievax_60

The solder ball shorting Q437 would explain all of the damage you have found so far plus more possibly. Check all resistors in the area including R573.
I would not expect any damage to the output transistors or Q445.
Faults that cause amplifier outputs to go DC don't necessarily cause any extra damage.

Already i checked all the components the damages are found as below

1.ZD410(shorted)
2.Q443 Q444, Q417(blown)
3.R551 and R493(burn mark)
4.C531 (blown)

Rest of all components i ddint find any damages also i checked with multi meter

I will do test run evening then i let you know

[srt1]

Hi.. i replaced Q417 with A684 transitor now i am geting -B volt around -50volt and i checked all chanell ther is no dc volt presents..but when i checked SL still ther have dc volt present.here i used a684 transisotor as replacemnt for q443 and q444 ..should i use same part number transistor here?

[rievax_60]

The correct transistors should be used to replace Q443 and Q444. What is the output voltage and polarity?

[srt1]

Originally Posted by rievax_60

The correct transistors should be used to replace Q443 and Q444. What is the output voltage and polarity?

Output voltage is 53 volt plarity positive .. also i checked voltage at emitter tied of Q443 and Q444 its show -13volt(negative), but in all other channels its 0.65volt (,positive)

[rievax_60]

Also check the Base voltages of Q443 and Q444. ZD410 should have about 5v across it. The combined voltage across R531 and R706 should be about 4.4v.
Have you replaced ZD410 with a 5.1v zenner diode? Are R531 and R706 ok?

[rievax_60]

Q444 might have a problem.

[srt1]

Originally Posted by rievax_60

Also check the Base voltages of Q443 and Q444. ZD410 should have about 5v across it. The combined voltage across R531 and R706 should be about 4.4v.
Have you replaced ZD410 with a 5.1v zenner diode? Are R531 and R706 ok?

R531 and r706 are ok .voltage accrose zd410 is 4.47 volt that is same on other channel also base voltage of q443 and q444 are same its -3.1volt but in other channel its 0volt

[srt1]

Originally Posted by rievax_60

Q444 might have a problem.

I used a684 instead of a992 as per data sheet a684 VCBO IS -60VOLT and Vceo is -50volt but for a992 is both are -120 volt ..tjis diffremce will cause transisotr not work?

[rievax_60]

Originally Posted by srt1

R531 and r706 are ok .voltage accrose zd410 is 4.47 volt that is same on other channel also base voltage of q443 and q444 are same its -3.1volt but in other channel its 0volt

What is the combined voltage across R531 and R706 ?

[srt1]

Originally Posted by rievax_60

What is the combined voltage across R531 and R706 ?

That is 3.9volt. in other channel also that is same

[rievax_60]

Im having trouble thinking of a definite reason. Somehow, current seems to be flowing from a negative rail to the emitters of Q443 and Q444 via some abnormal path. There might be a solder bridge somewhere or Q444 might be faulty.

[rievax_60]

I hope that you are not using acid flux? Are the 2sA684 new parts or pulls?

[srt1]

Originally Posted by rievax_60

Im having trouble thinking of a definite reason. Somehow, current seems to be flowing from a negative rail to the emitters of Q443 and Q444 via some abnormal path. There might be a solder bridge somewhere or Q444 might be faulty.

Ok that i am.checking now ..

[srt1]

Originally Posted by rievax_60

Im having trouble thinking of a definite reason. Somehow, current seems to be flowing from a negative rail to the emitters of Q443 and Q444 via some abnormal path. There might be a solder bridge somewhere or Q444 might be faulty.

That i am checking now

[srt1]

Originally Posted by rievax_60

I hope that you are not using acid flux? Are the 2sA684 new parts or pulls?

I am using fulx its like paste not liquid.2sa684 is new ..i hav 3 more with me i will try to replace..but when i am checking with multimeter it is ok... Any way i wil check the traces for any shortage

[rievax_60]

Also clean the solder joints after soldering. I use a toothbrush and turpentine. Alcohol is good.

[srt1]

Originally Posted by rievax_60

Also clean the solder joints after soldering. I use a toothbrush and turpentine. Alcohol is good.

I replaced q444 and cleaned now i am getinf diffrnt reading. Base of q443 is 0volt base of q444 is 6.3volt and emiter tied jucntion geting -4.6volt

[rievax_60]

It still looks like high PCB leakage. The 6.3v on the base of Q444 doesnt make much sense unless D449 and D550 are missing?

[srt1]

Originally Posted by rievax_60

It still looks like high PCB leakage. The 6.3v on the base of Q444 doesnt make much sense unless D449 and D550 are missing?

D449 and d550 is not present on board but its shows in scematic

[rievax_60]

Originally Posted by srt1

D449 and d550 is not present on board but its shows in scematic

Ok, that helps to make sense of the voltages. The leakage has to be between collector and base pads of Q444. Try to clean it again. Do you have any information about the flux?