Help with audio PS. Capxon caps. test methods without ESR.

[fastline]

I am fighting an audio amp that first developed a popping noise with no output, then worked fine, now does nothing but make a VERY loud hum in the 60-120hz area. I am being told that the PS filter caps are most likely the problem but all my tests come up good so far. Amp was built around 1998

These are black body capxon, 820uf, 200V. Resistance with a DMM climbs from 0 to 40m ohms, I charged them with a diode tester to 1.5V. They are holding 1.1-1.3V right now. I also used a friends cap tester and they all came in around 950uf.

I tested the bridge rectifier with a diode test and it tests fine. I am at a loss on this amp. I DO have a schematic if that would help anyone. I found one bad resistor that I repaired but that still did not fix me up. I was really hoping....

The mfg indicates the caps are a known issue but because the amp is so hard to install, I really want to know the caps are bad before replacing. I do not have ESR testing. How can I test these?

[Dgtech]

Re: Help with audio PS. Capxon caps. test methods without ESR.

You just tested them and found that they are bad. 950uF on 820uF is enough to make a difference. That is about a 20% increase per cap. Change them out and dont run the unit again until they are changed. You could be stressing other components.

I cant tell you that after you change them you wont have any problems cause I think you might have something else also going on there. But change em then test it and see what you got. Report back.

[Dgtech]

Re: Help with audio PS. Capxon caps. test methods without ESR.

Also, I have to add, OK... the power caps should be changed but I'd also think that the hum would be more in the other filter caps than just the power supply filter caps. I'm not sure exactly how that schematic would look like but I'd think there were multiple stages of amplification and at each stage there is (noise)filtration being done. Who knows, maybe the bad PS caps caused the other ones to have problems. Just a guess.

[fastline]

Re: Help with audio PS. Capxon caps. test methods without ESR.

The actual schematic calls for 1000uf caps. the 820s were in the first revision. I have never seen caps increase that much in cap but that is still within a 20% range of 820. Is there other tests? Will ESR prove them bad if they are? I could stop by a shop to test them I guess. Really want to find my issues because like you say, I could hurt more components.

The bridge diode tests fine so if the filter caps are good, that moves us away from the DC buss anyway.

[Th3_uN1Qu3]

Re: Help with audio PS. Capxon caps. test methods without ESR.

How loud is the hum? Is it like the volume is maxed? Does any audio get thru? If no audio gets thru besides the hum, your problem isn't the caps. You should go ask at diyAudio, they can help you on the matter more than we can.

[fastline]

Re: Help with audio PS. Capxon caps. test methods without ESR.

The hum is near max output and you certainly would not turn it on and then try to do further testing.

[stj]

Re: Help with audio PS. Capxon caps. test methods without ESR.

check the earthing,
and the caps in analog psu's cant be tested by most meters because it's the ripple handling that's important in analog stuff.
the ripple handling must exceed the power consumption of the circuit in order to keep the output stable.

[fastline]

Re: Help with audio PS. Capxon caps. test methods without ESR.

This is a switching amp if that changes anything. I am strongly looking at grounds right now because I just cannot find a single component that is bad yet and I find it real odd that it worked for me, I added a few screws, and now it hums VERY loud through the driver. My gut is saying I either created a ground it should have or deflected the PCB in a way that caused damage but I cannot find it...

I visited here to specifically cover the filter caps. I am trying to determine if they are bad or not and if they could really cause all this noise? Post above says no. I would sure think for it to be this bad, that caps would be showing all sorts of bad and they are not. Cap meter shows them good and they hold a charge... I know that does not prove them but they are certainly not open or shorted...

[Th3_uN1Qu3]

Re: Help with audio PS. Capxon caps. test methods without ESR.

So what amp is it exactly? Any schematic or service manual?

[fastline]

Re: Help with audio PS. Capxon caps. test methods without ESR.

The amp is a D class integrated sub woofer amp. The schematic is attached. I am still wondering if I have a ground loop issue that I created somehow when working on it.

I am still just totally baffled how I went from having it working, to adding just a few screws and now nothing but a hum. The hum certainly sounds like hum you might get from a guitar amp but VERY loud but I guess this is an 18" sub so it barks a bit..

I have tested the bridge on the bench and so far is testing fine. Caps sure look ok or good enough to run and should not do what I am experiencing. Just not sure what else would cause this noise.

[Dgtech]

Re: Help with audio PS. Capxon caps. test methods without ESR.

I'd definitely use a scope to identify the hum and trace out it's source. If no scope is available, and if you have a fluke, the hum could be measured with the HZ setting on the meter.
Start the divide and conquer method. Since you have a schematic, I'd use the computer to inject a known audio signal into the amp(you can find programs to generate these through audio output). Disconnect half of the circuit and see if that hum still exists and go from there.