Any electronics experts about (possible capacitor content)?

[m_c]

I've had an old UPS in the workshop for a while to keep some critical things powered up, but it died a few months ago, and I've only just got around to having a look at it.
Initially it tripped the main RCD a couple times, and having identified the UPS was the problem, powering it back up resulted in a bang and spark from within, and it blew it's 13A fuse.

I've just got around to stripping it, and the only thing I can see is what I assume is an old ceramic capacitor has split -
(split isn't visible in the pic, but it's split up the lower edge)

It goes between the leg of the diode, and the thermistor/surge limiter leg.
There is 47nF written on the silkscreen, but from what I know about capacitors, that isn't a 47nF capacitor.

I've not traced the circuit at all yet, but is it likely to cause any short term issues to just cut it out to check nothing else has been damaged?
Also, any suggestions for a suitable replacement?

 

[Sparky666]

Think the 3 is a multiplier, try a search, has helped me out a few times

 

[gaz1]

thats not split on leg it means nothing look elsewhere

look underneath at the board look for shatered pieces more so around burnt parts as much as you can smell them

 

[R Kraft]

That type of capacitor is called an orange drop.
0.047uf

 

[Chippie]

The cap is not the likely culprit.( 47nF…= 473)

If it’s blowing fuses, you have a short across the incoming supply…
Your dvm should help in locating the faulty part. got any better fotos showing the mains input side of things?

 

[voipio]

473 is basically 47 x 10^3 pF, i.e. 47,000pf, or 47nF. Looks a bit of a bodge. Has the UPS been in for repair before?

 

[ajlelectronics]

Chopper transistor is the place to be looking. What caused it needs to be investigated, can be dried out electrolytics, but check the circuit diagram if you can find one.

 

[m_c]

thats not split on leg it means nothing look elsewhere

look underneath at the board look for shatered pieces more so around burnt parts as much as you can smell them

So this big burnt split means nothing?

 

[ajlelectronics]

So this big burnt split means nothing?

Not really no, however it needs changing of course. It is probably across the incoming supply and the PSU will start and run without it, if it is where I think it is in the circuit.

It has clearly been replaced with an oversize component in the past.

 

[m_c]

This is a more general photo.
Output mosfets (at least I'm assuming it's using mosfets) are just out of shot in the top left, but they all look fine.

Incoming power is brown/blue wires.
Outgoing power are red/yellow/orange to a transformer with no ratings on it.

 

[ajlelectronics]

The way that the PSU works is to rectify the incoming AC mains to DC with diodes. That is then fed to an oscillator at about 60Kc/s which feeds a transformer. The oscillator transistor is in effect across that DC supply and if it can't oscillate, it protests by going s/c ant taking out the supply fuse.

There are generally one or two X class capacitors on the input for EMI suppression. They go bang once in a while.

 

[m_c]

Not really no, however it needs changing of course. It is probably across the incoming supply and the PSU will start and run without it, if it is where I think it is in the circuit.

It has clearly been replaced with an oversize component in the past.

I know it doesn't mean nothing, but can't be doing with Gaz thinking I've not bothered to look for any other obvious issues.

I might try cutting it off tomorrow and see what happens. It is part of the incoming power circuit. You can't really see it in the picture, but the surge limiter is connected to the same trace as the L in.
If it works without it, then I'll try finding a new one to fit.
If it doesn't work, then it'll probably be going in the skip, as I've got enough projects lying around.

 

[ajlelectronics]

A simple smpsu for illustration. Click here

 

[gaz1]

So this big burnt split means nothing?
View attachment 370446

that split is not shown on your first pic uploaded

it was 9.51pm before you posted a pic with a crack in it

to reply as if your on your high horse you should have posted clear pics to show that the capacitor was at fault in the first place but like everything else people dont look around the boards looking for other faults

 

[m_c]

I've just got around to stripping it, and the only thing I can see is what I assume is an old ceramic capacitor has split -
(split isn't visible in the pic, but it's split up the lower edge)

that split is not shown on your first pic uploaded

it was 9.51pm before you posted a pic with a crack in it

to reply as if your on your high horse you should have posted clear pics to show that the capacitor was at fault in the first place but like everything else people dont look around the boards looking for other faults

Perhaps you could read posts fully before responding?

 

[skotl]

...look underneath at the board look for shatered pieces more so around burnt parts as much as you can smell them

It tickles me that the UPS hides its broken bits under the circuit board

 

[Jan-DIY]

Cut out the cap for testing.

 

[m_c]

Cap cut, and it's no longer tripping the RCD, but it's dead to the world.
I did suspect the cap was more a symptom than the problem, so it's going in the skip.

 

[Seadog]

Nothing to be lost by replacing the cap and seeing if it works.

 

[Chippie]

Wish I were closer, I’d take it…