Pioneer SX-950 Speaker Pop at Power-Off

[Brivan]

Thank you so much for your response.

I will definitely try these 2 parts 1st and go from there.

Okay. I'm interested in your results since I've now had two of these receivers with the same popping noise at power-off and replacing those two components were the only things that made a big difference. I'd like to run across another one with the same problem, then make sure the problem wasn't worse because of being connected through a DBT (although I was running through all three 60-watt bulbs). Unless I have a good reason not to, I prefer leaving receivers connected through the DBT while I'm working on them - just in case I do something dumb!

 

[Scheid]

I will definitely update you with the results once I get them. It could take me a while if I don't have the correct parts on hand.

I have a 1kVA UPS that I use to power the units that I am working on. It does a great job of monitoring the voltage and has a display where I can adjust Voltage, monitor loading, etc.

 

[Scheid]

I did happen to have these parts on hand and was able to switch them out and..... this mod is working perfectly !!!

This 950 is now powering off without any sound coming through the speakers at all. I have even tested
it with the volume up pretty high and still perfect results. Not that I ever power down with the volume up, but
I just had to test it anyhow.

Thank you so much for sharing this extremely helpful information.

The world is now a better place.

 

[Brivan]

I did happen to have these parts on hand and was able to switch them out and..... this mod is working perfectly !!!

This 950 is now powering off without any sound coming through the speakers at all. I have even tested
it with the volume up pretty high and still perfect results. Not that I ever power down with the volume up, but
I just had to test it anyhow.

Thank you so much for sharing this extremely helpful information.

The world is now a better place.

That's good to hear! I hate to leave open-ended threads on AK and like to reach a conclusion so others may benefit.

The only caveat with this fix is that I'm afraid it's masking another problem. But, even with Mark's help, I wasn't able to find what was causing this. It left the factory working fine with all the original parts, so what changed and why do we need to make those two small modifications for the problem to go away? At any rate, the fix doesn't seem to hurt anything.

I wonder if the SX-950 is the only receiver in the X50 line to ever exhibit this issue - or can it happen in an 850, 1050 or 1250? I dunno.

 

[markthefixer]

850 and 950 use exactly the same power supply and protection.

It's quite likely these two mods to drop protection a bit quicker, on the protect board, are masking a supply voltage that also drops TOO quickly when AC is removed.
Anything from a popped fuse (full wave becomes half wave) to a bad rectifier, to a leaky capacitor. Perhaps elsewhere on the chassis.

 

[Brivan]

850 and 950 use exactly the same power supply and protection.

It's quite likely these two mods to drop protection a bit quicker, on the protect board, are masking a supply voltage that also drops TOO quickly when AC is removed.
Anything from a popped fuse (full wave becomes half wave) to a bad rectifier, to a leaky capacitor. Perhaps elsewhere on the chassis.

Next time I get my hands on another SX-850 or 950 with that same issue, I'd like to try to dig a little deeper and see what can find in regards to what you've mentioned above. I'm getting an SX-880 that has a protection relay drop-out issue at higher volume levels and I know there's a capacitor replacement "fix" for it, but that's another case where the evil is likely lurking in some hard-to-find place and replacing that cap is only curing the symptom. I'll start another thread on that, if needed.

 

[NHDoc]

I also had a 950 with the pop at shutoff. It was volume dependent and though not terribly loud just didn't seem right.

The relay did seem to stay closed a tad longer after shutting off the power than it does on my other Pioneers so I tried the mod to the protection circuit and it fixed the problem and the relay closes a little faster now. Since the receiver seems fine otherwise I didn't feel it was necessary to delve further into it at this time but if the problem comes back I will look more for the root cause of the pop. It seems to be a common problem on this model however and I am sure there are lots of people who experience it who don't even realize it is not supposed to make any noise at power-down.