Pioneer VSX-520-K Protection problem

[srt1]

Re: Pioneer VSX-520-K Protection problem

[QUOTE=rievax_60;770457]If the input differential transistor pairs lose Emitter current, the amplifier outputs will go to a high positive voltage. There is a 12v rail that is common to all channels.[/QUO

were is the differential transistors pairs? i attached here service manual ..can you explain where its coming there is no 12volt rails as per schematic

[rievax_60]

Re: Pioneer VSX-520-K Protection problem

The 2 PNP transistor in the input stage with their Emitters tied together. The 7.5K resistor supplies current from the 12v rail.

[srt1]

Re: Pioneer VSX-520-K Protection problem

The 2 PNP transistor in the input stage with their Emitters tied together. The 7.5K resistor supplies current from the 12v rail.

Thank you but there in no 12volt rail in Amp section my receiver is vsx 522, i found there transistors with emitter tired also one more transisitr beside that its part no KTA1024

[rievax_60]

Re: Pioneer VSX-520-K Protection problem

Yes, you are right I was looking at a different model. Measure the voltage at the input capacitors like C440. There would be 0v on both sides in a normally working amplifier.

[srt1]

Re: Pioneer VSX-520-K Protection problem

Yes, you are right I was looking at a different model. Measure the voltage at the input capacitors like C440. There would be 0v on both sides in a normally working amplifier.

ok i will check it .. can you explain why there is KTA1024 tranistor ?it is not in vsx 520 model. also i found a 5.1olt zener diode...

[rievax_60]

Re: Pioneer VSX-520-K Protection problem

Also check the voltages on Q417. It supplies filtered negative rail voltage to the Voltage Amplifier stage in all channels.

[rievax_60]

Re: Pioneer VSX-520-K Protection problem

ok i will check it .. can you explain why there is KTA1024 tranistor ?it is not in vsx 520 model. also i found a 5.1olt zener diode...

They form a constant current supply for the differential pair. Search for "Transistor Long Tailed Differential Pair".

[srt1]

Re: Pioneer VSX-520-K Protection problem

They form a constant current supply for the differential pair. Search for "Transistor Long Tailed Differential Pair".

Thank you i will chek it today evening.what would be the expected voltage at constant current source? Ie collector pin of q413

[rievax_60]

Re: Pioneer VSX-520-K Protection problem

Thank you i will chek it today evening.what would be the expected voltage at constant current source? Ie collector pin of q413

Don't worry about the current sources because they work independently of each other. We are looking for a problem that has an effect on all channels like missing negative rail to the VA stages.

[srt1]

Re: Pioneer VSX-520-K Protection problem

Yes, you are right I was looking at a different model. Measure the voltage at the input capacitors like C440. There would be 0v on both sides in a normally working amplifier.

hI , I checked the voltage at both end of c440 , its showing 54 volt !

[rievax_60]

Re: Pioneer VSX-520-K Protection problem

hI , I checked the voltage at both end of c440 , its showing 54 volt !

That was unexpected. Not really certain what to do next. Is the amplifier fully assembled? all of the screws are in place. Try measuring voltages at other places like the main rails and ground lines like AGND. Looking for anything obviously wrong.

[srt1]

Re: Pioneer VSX-520-K Protection problem

That was unexpected. Not really certain what to do next. Is the amplifier fully assembled? all of the screws are in place. Try measuring voltages at other places like the main rails and ground lines like AGND. Looking for anything obviously wrong.

I taken out the amp out and connected the power cable actually ther is no ground connection to amp board.. is it cause 54 volt at input capacitor?

[srt1]

Re: Pioneer VSX-520-K Protection problem

I taken out the amp out and connected the power cable actually ther is no ground connection to amp board.. is it cause 54 volt at input capacitor?

i connected CN400 cable and then i measured the input volatge at input signal capacitor , now it shows 0 volt at negative side and 18volt at positive side of input capacitor

[rievax_60]

Re: Pioneer VSX-520-K Protection problem

I taken out the amp out and connected the power cable actually ther is no ground connection to amp board.. is it cause 54 volt at input capacitor?

There will be many things that must be left connected. I don't know what is ok to be left disconnect.
The manual should say how to properly open the amplifier for better access while keeping important grounds connected.
This amplifier looks difficult.
It is best to try to get readings with the amplifier fully assembled.
Some of the screws in the back plate and possibly other places can be important grounding connections.

[srt1]

Re: Pioneer VSX-520-K Protection problem

There will be many things that must be left connected. I don't know what is ok to be left disconnect.
The manual should say how to properly open the amplifier for better access while keeping important grounds connected.
This amplifier looks difficult.
It is best to try to get readings with the amplifier fully assembled.
Some of the screws in the back plate and possibly other places can be important grounding connections.

You are right, CN400 cable was disconnected for proper access after connecting i measured the voltages at input signal capacitorits show 0volt at negative side of capacitor and 18volt at positive side

I am measuring the volatges while keeping the negative probe at chassis.

[rievax_60]

Re: Pioneer VSX-520-K Protection problem

It is likely that there is a problem with th -B rail supplied by Q417. It should be about -50v.

[srt1]

Re: Pioneer VSX-520-K Protection problem

It is likely that there is a problem with th -B rail supplied by Q417. It should be about -50v.

Yes you are right, q417 already blown and its two resistors, But i am trying to get same part number, unfortunately its not available in market and its take one week to arrive, instead of A992, can i use A92? , i checked the specification both are almost matching except its pin arrangement(pin arrangement is not an issue as long as i can bend it).

[rievax_60]

Re: Pioneer VSX-520-K Protection problem

Yes you are right, q417 already blown and its two resistors, But i am trying to get same part number, unfortunately its not available in market and its take one week to arrive, instead of A992, can i use A92? , i checked the specification both are almost matching except its pin arrangement(pin arrangement is not an issue as long as i can bend it).

The transistor specs won't be critical for that application. There must have been a reason for the failure. At least check for a short on the -B rail to ground. Depending on how difficult it is to get to those parts, you can do an initial test run with just a resistor feeding the -B rail. The transistor just functions as a ripple filter and is not needed to make the amplifier work.

[srt1]

Re: Pioneer VSX-520-K Protection problem

The transistor specs won't be critical for that application. There must have been a reason for the failure. At least check for a short on the -B rail to ground. Depending on how difficult it is to get to those parts, you can do an initial test run with just a resistor feeding the -B rail. The transistor just functions as a ripple filter and is not needed to make the amplifier work.

Ok, i tel you the exact history of this VSX-522, i got this from one of my friend and it was not in working condition , problem is circuit protection shutdown the receiver itself. so first i cheeked for any transistors short in final amp stage and i found that SL channel q446 have internal shortage that cause protection circuit activate, also so i found 3 resistors have blown mark(R561, R562, R569),
so what i did was i just removed the shorted transistor ie q446 , also i disconnected the legs of q440(when i checked with multimeter this transistor have no shortage and also its showing same reading as other channels so i except q440 transistor no need to replace ),. Then i power the up the amp, its worked no issues at all , then next week i decided to replace the blown q446 and associated resisotors but while doing this a lead ball fall donw to amp board and i didn't see where its gone. when i checked on the board i never see it anywhere , but when i power the amp some fumes came from, actually the lead ball cause shortage of pins of q437 it was sticking ther.due to this q443, q444 and zd410(zener doiode) got blown, but after your reply checked q417 that also i found blown. even q443 , q444 blown i thought other channel will be work fine, but i am wrong. after blown issue i tested the amps without the signal input connector, but i connected back(as per your reply) as it supplying AGND to pre-stage amp section, i will do a test run with a 33OHM resistor, then i let you know the result

[rievax_60]

Re: Pioneer VSX-520-K Protection problem

Ok, i tel you the exact history of this VSX-522, i got this from one of my friend and it was not in working condition , problem is circuit protection shutdown the receiver itself. so first i cheeked for any transistors short in final amp stage and i found that SL channel q446 have internal shortage that cause protection circuit activate, also so i found 3 resistors have blown mark(R561, R562, R569),
so what i did was i just removed the shorted transistor ie q446 , also i disconnected the legs of q440(when i checked with multimeter this transistor have no shortage and also its showing same reading as other channels so i except q440 transistor no need to replace ),. Then i power the up the amp, its worked no issues at all , then next week i decided to replace the blown q446 and associated resisotors but while doing this a lead ball fall donw to amp board and i didn't see where its gone. when i checked on the board i never see it anywhere , but when i power the amp some fumes came from, actually the lead ball cause shortage of pins of q437 it was sticking ther.due to this q443, q444 and zd410(zener doiode) got blown, but after your reply checked q417 that also i found blown. even q443 , q444 blown i thought other channel will be work fine, but i am wrong. after blown issue i tested the amps without the signal input connector, but i connected back(as per your reply) as it supplying AGND to pre-stage amp section, i will do a test run with a 33OHM resistor, then i let you know the result

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.