Pioneer VSX520 No power

[smk279]

I trash picked this receiver and it has no power It's very dusty inside I took out the power board How can I find out what's wrong with it? I notice when I plugged it into the wall or when I press the power button there's no click It only has one fuse it shows continuity

[wasedadoc]

I put 'Pioneer vsx520 service manual' into Google and the first hit was to a free download.  Did you not do the same?

[Zucca]

I would check with a DMM is the main voltage arrive to the board.
If you are lucky it is just a bad mains cable.

Please be careful mains voltage can kill you.

[smk279]

Yes I downloaded it yesterday

[Jeff eelcr]

How would you know if something was burnt open, not by looking, clean it first.
Jeff

[smk279]

I found this av receiver had modular design so I took the whole thing apart, I even removed the power transformer from the chassis Can I plug the power board into the transformer and plug it in without connecting the amplifier board so I can see if the relay clicks when I plug it in, although I don't know if it's supposed to It would surely be supposed to click when I press the power button which I could also connect

[smk279]

Yes, I have to check resistors at their bases because above that the leads are brown rust color and I don't get any reading at all Testing them at their clean bases where they haven't oxidized with my DMM set to beep for continuity some of them show readings ranging from 600 to 1900 instead of beeping

[Jeff eelcr]

I am guessing you do not have a variac, plug and pray is not a good troubleshooting method.
The service manual was a good start, next a good visual inspection then what voltages are there and which voltages are not?
These are the ones that have to be there before power up that I am refering to.
Is the relay good? Is its drive circuit good?
Take your time, be careful, get more experiance, check grounds, check current draw of unit.
Jeff

[smk279]

Thanks but why do some of the resistors show a reading instead of causing the DMM to beep?

[Jeff eelcr]

The beep is for (shorts) a direct connection not to gage resistors.
Higher value resistors will not beep low value ones will.
Jeff

[FIXITNOW2003]

Have you done the reset on page 47 ?
to clear errors summery as bellow

If the unit is automatically shut off after a DC error is detected, no key input will be accepted afterward.(The power will not be turned ON.)Simultaneously holding the [ADVANCED SURROUND] and [STANDBY/ON] keys on the front panel pressed for 2 seconds will cancel Key Input Inhibition mode after a DC error detection and turn the unit ON.

[smk279]

I already took the whole thing apart

[smk279]

I think it's too late for me to try that with the entire unit disassembled

[smk279]

The transistor in the center of the photo is shorted and so is the brown metal oxide capacitor showing above it How do I change them do I have to bend all of the leads on all the transistors cause I'll be bending the board so I don't have to unscrew all of the transistors Is that the way to do it?

[wasedadoc]

No, that is not how you do it!

Give it a proper clean up.  It looks like the transistor leads are soldered at the board edge and you can desolder each lead of that transistor one lead at a time and bend them slightly away from the board.  There appears to be an hole in the board for screwdriver access to remove the transistor from the heatsink.

It is very unlikely that the ceramic capacitor is shorted.  Probably it is across a junction of the shorted transistor.

If you do have to remove the board, free all the transistor leads as above and leave them mounted on the heatsink.

To be brutally frank, you have not yet instilled any confidence in me that you have sufficient competence to bring this attempted repair to a successful conclusion

[smk279]

Do I need to put fresh heatsink plaster when I put the new transistor on? I'll have to order it cause I don't have any

[wasedadoc]

It is not "plaster".  It is called heatsink paste or heatsink compound.  You should remove the remains from the heatsink and apply a small amount forming a thin layer over all the metal back of the new transistor.

When you have removed the old transistor, check if the capacitor still appears shorted.

[smk279]

I removed the transistor and the ceramic capacitor no longer shows a short

[smk279]

Is it different from the stuff used for computer CPU's

[wasedadoc]

Is it different from the stuff used for computer CPU's

No.

[smk279]

I replaced the bad transistor but it still doesn't power on How do I  test the transformer

[MathWizard]

Well IDK this model, but it might need some signal from another PCB, to be able to power up fully. What all chips are on the PSU PCB ? At some point make sure they all get power. It could be mainly just discrete BJT circuits, I should find the schematic.

Go on youtube and watch some stereo PSU repair video's. You can check a lot of stuff un-powered, with just a DMM. And I'd solder on a some test wires, like on the GND of the secondary side of the transformer, maybe after a rectifier.

Resistance on a DMM can sometimes be good enough to check a transformer, but yeah I know what to expect. The best test for your transformer, is just plug in the PSU, and measure the transformer AC output, and it should lead right to rectifier circuits, and have a pretty stable DC level, a few volts ripple maybe. I need to look at the schematic.

Also, if time is no concern, you could remove most of the caps, at least the electrolytic ones, and check them. Then with them out of circuit, un-powered with a DMM, you probably would find most stuff that could gone wrong on a linear PSU, like some diode or resistor. or bad BJT.

Are any of the relay's part of the power supply circuits themselves ? They go bad, but also need control signals, that probably comes from the main MCU somewhere on another PCB. But it's not hard to make a little circuit to turn on a relay, if that signal was all that's missing.

[Laval]

I have worked on a Pioneer VSX-832, it looks like the VSX-520 has many similarities. On the 832, the AC line cable is connected to a board which is nothing more then a small switch mode power supply that is always energized. It powers the standby system. On the small SMPS bord there is a relay which energizes the primary winding of the main power supply's transformer when the amplifier is turned on. Make sure that relay is working. Also check if you have AC on the SMPS. There should also be some connector on the SMPS that runs to other boards. On the 832, the pinout of all connectors is written on the boards so you should know which is +12 V, GND, etc. Assuming you have AC, make sure these voltages are OK.

Also, you said you changed some of the output power transistor, make sure you check the emitter resistors. They should be close to the transistors and they usually have a value below 1 ohm. Make sure they are neither short nor opened.

It would help to have clear pictures of all the boards. Also clean these boards. There is useful information written on them.


EDIT:

1. When I get back from work, I'll post annotated pictures to be clearer. The relay and it's driving circuit can be tested off line using a bench power supply. If it works, then the controlling circuit (MCU/MPU) will need to be investigated.

2. If you test the SMPS power on relay it would be a good thing to do it with all the other boards disconnected. Forcing a power on may blow more things up. It is quite possible that the controller board (the one with a processor) is still detecting a fault and doesn't want to power the device.

[eetechTom]

The blue resistor to the left of the brown capacitor you initially thought was shorted appears to be burned. Have you measured its value? If one of the output transistors failed I would be sure to check the transistor in the previous stage as well.

[Laval]

Here is a couple of pictures of the VSX-832 standby supply. The red circle is the AC line, the yellow is the transformer's primary winding. The blue circle is the connector from the control board IR detector (MPON) and power on switch (SWPON). The white and black markings on the other side are the relay switch which connects the AC line to the transformer primary when on and the relay's coil. Applying 0.9-1.0 v on the MPON pin of the connector when AC is connected will trigger the relay if it works.

Your board may be different but it should follow the same logic.

Like eetechTom said, it is important to test the resistor near the output transistors just don't forget to de-solder one leg to do it. If the standby relay bord works, it would be wise to check the transistor/resistors of the previous stage as well.

I hope this helps.