No sound from 2 channels in amplifier Pioneer VSX-321

[xiwi]

I had 5.1 Pioneer VSX-321 600w perfectly working that I left in a box for 3 years without touching it. After all this time I tried it again and no sound is coming out from central and subwoofer channel. The problem comes from the amplifier, not the speakers.

My idea of electronic in general is below than none so I just brought it to repair. The problem is that one guy couldn't find the issue and suggested me to buy a newer device. And someone else tried to charged me more than if I buy a second hand one (and probably working since day 0). I'd like to try my last chance here. I can try to fix it myself with some help. At least I have a welder and some hope. Not a multimeter but I could get one if necessary.

This is what I tried to identify the issue:
- Move the speakers to other channel to check they work fine and double check the problem is the amplifier
- Apply some heat directly on the area where I connect the speakers wires just in case the weld is loose
- Check for capacitors. Can't see fluid coming out or any bigger than others
- Check motherboard from both sides trying to find anything weird
- Reset the device to factory settings
- Speakers mode test to try speakers separately with a buzz. So no sound configuration is affecting the channels
- Check transistors and apply extra weld as suggested here with similar issue and device: https://youtu.be/0S4o8Xcc-3E

I took some pictures:
https://ibb.co/JrWYpG0
https://ibb.co/q5QX2Yz
https://ibb.co/JvWqn4Z
https://ibb.co/nRC7nrz
https://ibb.co/ygSVkrp
https://ibb.co/TPftQDV
https://ibb.co/0yjyQ5h
https://ibb.co/Q8pKrpf

transistors:
https://ibb.co/g9q81JS
https://ibb.co/hgWf8J5

Not sure if this is enough information. Let me know anything and I'll try it.

Thanks everyone!

[wasedadoc]

All speaker outputs go through relays.  Each relay switches two speakers.  The Centre and SubWoofer go through the same relay (RLY5).  Perhaps that relay is not operating.

Service Manual can be downloaded. https://elektrotanya.com/pioneer_vsx-321.pdf/download.html

[themadhippy]

before ripping the back of have you double  triple checked  all the settings and options are correctly set up

[wasedadoc]

Further to my post above I have marked RLY5 and R23 on the attached image.  There should be close to +12 volts with respect to chassis on both ends of R23 when Centre and SubWoofer are expected to be working.

[xiwi]

Good to know, I'll check that out

[xiwi]

what do you mean? I reset the ampli and I'm using a demo test

[xiwi]

Is there something I could check from it? As I mentioned my technical knowledge here is below 0.

[wasedadoc]

I cannot be certain but the most likely reason for those two channels not giving output is that the relay is not operating.  There is more than one fault which could cause that but the first thing is to find out if the relay is working or not.  As you have no test equipment but you do have a soldering iron then you could solder a piece of wire to bypass the relay contacts of the subwoofer channel.

The relays are there for two purposes:

1.  They connect the speakers to the power amplifiers shortly after those are powered on and shortly before they are powered off.  This is to avoid clicks and thumps from the speakers at switch on and switch off.

2.  They disconnect the speakers to protect them if there is a fault in a power amplifier.  There is only one signal from the protection sensing circuit into the microcomputer which controls the relays.  When protection operates, all the relays disconnect the speakers. As some of the channels are outputting sound then we can be sure that the centre and subwoofer channels do not have any fault which would damage a speaker if we bypass the relay.

Solder a piece of wire to join the two wire links I have marked in white on the photo.  Be absolutely sure that there is no bridging to nearby wire links or components. Be absolutely sure that both ends are well soldered and will not come come off accidentally and touch anywhere else.  Failure to comply with those last two sentences could lead to serious damage.

Then with the unit powered off connect only one wire of the subwoofer to the black subwoofer terminal.  Then power on.  Wait 30 seconds and connect the other subwoofer wire to the red terminal.  Select the test/setup mode which should produce noise from the subwoofer.  If it does then we are on the right track.

Switch of the test signal.  Carefully disconnect the subwoofer from the red terminal.  Switch of the power. Disconnect from the black terminal.  Unsolder the wire you added.

[xiwi]

I don't have the equipment but I could buy it. That's not a problem.

Would that be easier maybe? I could check if that's dead or not without creating some serious damage as you mention (even being careful). Probably I could follow this: https://www.wikihow.com/Test-a-Relay

[wasedadoc]

Almost nothing in that "relay testing" page is useful in your situation where the relay is in the equipment.  You cannot remove it with only a soldering iron.

The objective at this stage is not to test the relay itself, but to test if the lack of output is because the relay is not operating.  There is a difference.  If the relay is not operating there are several possible causes.  These include the relay itself, the back emf diode across the relay coil, the 10 ohm resistor in series with the relay coil, the two transistors in the circuit that drives the 12 volt relay coil from the lower voltage logic level output of the microcomputer and the microcomputer itself.  Little point in going to the trouble of testing the relay if we don't even know that it isn't operating.  And even if the bypass test does show the relay is not operating the next step would not be to test the relay.  I would ask you to get a multimeter and measure some voltages.

An alternative is to make the bypass on the underside of the board.  Small piece of wire or a solder blob across the two points with the red line in the drawing.  This is the view from the top of the board.  You'll need to find those two points on the underside.

If you don't have the competence or confidence to temporarily add a bypass wire then there isn't much prospect of you succeeding to repair the unit.  Better take it to someone who knows what they are doing.  Clearly the two you already asked do not.

[xiwi]

Understood. Let me try to find someone to help me out and I'll share with him this info.

Thanks!

[xiwi]

Sorry for the delay, I was on holiday these days.

Following your initial suggestion I tried to join RLY5 connections behind the motherboard so I removed everything to discover the oposite area and I saw this: https://i.ibb.co/JykkPfJ/Screenshot-2022-11-04-at-12-08-57.png

I'm pointing at the 3 relays being the one in the middle RLY5. This was already connected as su suggested. Probably they tried exactly the same fix, didn't work and found the real one. When I told them to not fix it, they probably forgot to remove that. Makes sense or that's something it should be like that?

[wasedadoc]

No, it isn't normal for those wires to be there.  Someone has previously tried bypassing the relay.  So the fault is elsewhere.  The next place that I would check is IC605.  That is a 2 channel buffer amplifier.  One half handles the Centre Signal and the other half handles the SubWoofer.  Lower right corner of the schematic on page 72 of the Service Manual and upper right corner of the board underside iayout on page 92.  Unfortunately, investigating that is going to be beyond your capabilities and equipment.  To test really needs an oscilloscope and the knowledge how to use it.  If that IC is faulty it is a standard part and only a few Euros but with 8 pins, an ordinary soldering iron makes its removal not straightforward.

[Audiorepair]

Most op-amps fail full DC, so if IC605 or indeed any other similar op amp is faulty, it will most likely have full power supply DC on its outputs on pins 1 and/or 7.
If the output pins measure zero volts DC on a multimeter, the IC is probably good.


I will often just quickly go round all the op-amp output pins with a multimeter to find any that are DC, it can save a lot of time and effort.

[xiwi]

if that shouldn't be there, shall I remove it? Just in case that creates other issue as you mentioned before.

Yeah, it seems to be a bit more difficult so I guess I'd need a more professional hand on this. Thanks anyway

[wasedadoc]

Yes, remove those links.  Tell anyone else you ask to repair it that bypassing the relay has been tried.

The outputs of that buffer IC are dc coupled to the connector on its board. That board is right at the top so should be quick and easy to check the voltages and signals as suggested above.

[xiwi]

Makes sense. Thanks