Nexo Ps10 amplifier (power supply problem)

[Joe bags]

Hi Guys

I have a Nexo Ps10 with a power supply issue. I was told that one of the caps on the power supply came loose and fell out of the circuit board. The amp continued to be used and performed well for a time. Then at one gig smoke started coming out of the amp. When I looked inside the amp I found blown caps in the power supply.
I replaced all the blown caps, tested the amp with speakers and sound and all seemed fine.

The amp was tested again before being sent out on a gig and smoke bellowed out of the amp again.
The same capacitors had blown again.

There are 16 3300uf @63v caps on the power supply board.

So i'm looking for advice to continue this repair.
Should I replace all the caps on the board?
Should I put higher voltage caps in?
Should I suspect 1 of the 2 voltage rectifers?

Any comments welcome.

Regards

Joe

[soundguruman]

We would not be able to diagnose anything without the schematics, which you could post here.
But you probably need test equipment and soldering equipment, etc...

[soundguruman]

We would not be able to diagnose anything without the schematics, which you could post here.
But you probably need test equipment and soldering equipment, etc...

Post pictures, with good lighting and focus, of what you have done so far.

[Jazz P Bass]

A rectifier that is going bad may cause caps to fail.

[imix500]

When the first cap went bad did you replace all of them or just the ones that leaked?
If one goes, it's usually a sign they are all on their way out. All caps have a lifespan, and I would say they are done in your amp.

[52 Bill]

If one goes, it's usually a sign they are all on their way out. All caps have a lifespan, and I would say they are done in your amp.

I agree in principle here, but he stated that he replaced only the blown ones and then the same caps blew out again.

I'd like to see how these are wired, that would lead us to a possible cause of the problem.

[imix500]

Ah, I misread that. It's also possible many of the other caps have gone high impedance (though not often) and the new caps are carrying the load resulting in ripple beyond their ratings.
Agreed though it would be great to see pics.

[Joe bags]

I don't have schematics. I replaced 3 caps on the board. On test one of the new caps failed badly and one the older caps started to bulge. I have proper test equipment to carry out the repair.

Here's some pics anyway.


Amp overview by Joebags1, on Flickr


Pwr Sply 1 by Joebags1, on Flickr


Pwr Sply 2 by Joebags1, on Flickr


Rectifier by Joebags1, on Flickr

[J M Fahey]

1) what's the caps voltage rating and the actual rail voltage?
They might be uncomfortably close.
2) replace caps (being very careful with polarity and such, *anybody* can make a mistake), turn amp on but without signal, touch all caps every couple minutes, for, say 1/2 or 1 hour, any becomes hot?
3) connect a suitable load, apply signal and drive amp almost to clipping (that's what the end users will do anyway )
Any undue heat?
4) the amp might have quad rail supplies (Class H, etc.).
Suppose it's +/-40 and +/-80V
It might use stacked same value caps (say, 10000x50V each) so all would be the same, *OR* non-stacked; say, half 10000x50 and half 10000x100V . made-up examples to understand the problem.
If, say, a 100V one fell, and you replaced it with a lower voltage one, based on the one just by it, you might have a (bad) surprise.
Please check and confirm.

EDIT: or the one you replaces went upside down. It failed instantly (reverse polarized) and the one in series with it was overvoltaged (which is bad but not so fast ) and bulged.
Anyway post your findings.

[Joe bags]

Just replaced all the caps in the power supply. Preliminary tests are good. Left amp on for half an hour with no signal or load. Checked caps for undue heat. None found. Hooked up a load and played some music through it for an hour or so and all is still well. I'll get back to it on Monday and run the hell out of it and see how she gets on.

Thanks for the comments it's good to think out loud!