Another rescued PC, another blown power supply

[SMichelsen]

So here I am with this AVL Genesis PC (by Eagle), after it sat in a humid basement for 30 years. Here's an image of what it looks like in happier times.



I booted it up after scrubbing the rust out of all the connectors. Surprisingly, it ran well for about five minutes, though it declared that there's some sort of issue with the floppy - but that's for another time. After the five minutes there was a nice pop-fizz sound, and I let the smoke out. I opened it up, pulled the power supply, and it looks like this is what failed. Can someone please confirm this "don't look like it ought to" and suggest a modern replacement? Thanks!

 

[Ruud]

It is, what they call, a RIFA. You can cut it out and the PSU will work again. It is needed to filter irregularities on the the power coming from the outside but also to filter those coming from the PSU. (Dutch: ontstoringscondensator, translation: interference suppression capacitor) But find a new one to keep the net "clean".

 

[modem7]

Can someone please confirm this "don't look like it ought to"

See the 'Line Suppression Capacitor' section of [here]. Quite commonly referred to as 'safety capacitor'. This aged component is a high failure rate one.

'Rifa capacitor' is an informal name, not a technical name. RIFA is a manufacturer of capacitors (and other things).

Yours is a 0.6 µF (micro Farad) of class X. Rated at 250V AC, so that the capacitor can be used worldwide.

You should be able to find these online by searching using '0.6uf safety capacitor' or '0.6uf line suppression capacitor'.

 

[Robbbert]

Yeah that type of capacitor is notorious for blowing up (literally) after a number of years.

 

[SMichelsen]

See the 'Line Suppression Capacitor' section of [here]. Quite commonly referred to as 'safety capacitor'. This aged component is a high failure rate one.

'Rifa capacitor' is an informal name, not a technical name. RIFA is a manufacturer of capacitors (and other things).

Yours is a 0.6 µF (micro Farad) of class X. Rated at 250V AC, so that the capacitor can be used worldwide.

You should be able to find these online by searching using '0.6uf safety capacitor' or '0.6uf line suppression capacitor'.

Thanks for that, and the link to the minuszerodegrees page that says:

When sourcing a replacement for a faulty item, note that you need to match three things:
1. Capacitance (e.g. 0.1 µF);
2. Maximum working voltage (e.g. 275 volts AC) (can use something rated higher);
3. Class (i.e. replace X2 with X2, replace Y2 with Y2), noting that per here, some substitution of class is possible.

I came up with a cap from Mouser. Please take a look - does this look correct?

https://www.mouser.com/ProductDetail/KEMET/R46KI360045N0M?qs=sGAEpiMZZMsh%252B1woXyUXj4OxC4raikkmD71dq5qYX9g%3D

 

[modem7]

I came up with a cap from Mouser. Please take a look - does this look correct?

Looks good, but there is one thing for you to check. The quoted part has a lead spacing of 15 mm. Are the holes in your PCB spaced at 15 mm? From what I have seen, the 'block form' line suppression capacitors have two possible lead spacing, and sometimes, a PCB has two sets of holes to cater for both possibilities.

 

[SMichelsen]

Looks good, but there is one thing for you to check. The quoted part has a lead spacing of 15 mm. Are the holes in your PCB spaced at 15 mm? From what I have seen, the 'block form' line suppression capacitors have two possible lead spacing, and sometimes, a PCB has two sets of holes to cater for both possibilities.

Thanks for that; the holes for the exiting cap are 20mm apart. That MIGHT be close enough to fudge it; those pins don't look very long...

 

[SMichelsen]

Looks good, but there is one thing for you to check. The quoted part has a lead spacing of 15 mm. Are the holes in your PCB spaced at 15 mm? From what I have seen, the 'block form' line suppression capacitors have two possible lead spacing, and sometimes, a PCB has two sets of holes to cater for both possibilities.

I got the bad RIFA-branded cap out. You were correct; there are multiple holes for various pin widths.
Here's a pic of the space that the old cap left, with the various holes for pins. The old cap occupied the outer pins and was 20mm. The new one is 15mm; there's no doubt it'll fit.
There's also a pic of the side of the cap that couldn't be seen before removing it.

 

[Mochatea396]

Isn’t that such a horrible smell it leaves behind? It just smells like burnt short circuited old electronics. And it lingers in the room for days. I change them out whenever I see one before they fail mainly to avoid that stench.

 

[SMichelsen]

Isn’t that such a horrible smell it leaves behind? It just smells like burnt short circuited old electronics. And it lingers in the room for days. I change them out whenever I see one before they fail mainly to avoid that stench.

Indeed. And the smoke is heavy (oily?) - it hangs in the air and dissipates slowly. At least it helps one recognize what the problem is when it happens!

 

[seaken]

It is, what they call, a RIFA. You can cut it out and the PSU will work again. It is needed to filter irregularities on the the power coming from the outside but also to filter those coming from the PSU. (Dutch: ontstoringscondensator, translation: interference suppression capacitor) But find a new one to keep the net "clean".

I have read this several times, that we can just cut it out and the PS will still work. But I am wondering how this works? If we just cut it out isn't that breaking the in-line circuit? How does the PS know to re-route around the missing capacitor to keep going? Rookie question, I know.

Seaken

 

[wrljet]

Most of those RIFAs are across the AC line, for EMI filtering, etc. They aren't breaking the circuit when they are missing. And aren't not actually needed for the power supply to work.

 

[seaken]

I clearly have a lot to learn. But I won't hijack this thread. I'll bring it up on my own thread. Unless the OP want to pursue this further?

Thanks

 

[wrljet]

As an example, here's part of an IBM PC AT power supply. The capacitors on the left side, C4A and C5A are RIFA style capacitors.

Here's a little blurb about these X/Y Class capacitors

 

[seaken]

Thank you, that was helpful. I'll keep reading up on this. What I don't know about electricity is a lot.

Seaken

 

[wrljet]

While fiddling with this, keep in mind there are lethal voltages in these switching power supplies.

Notice the point in the upper right, has a test voltage of 323V DC there.

 

[seaken]

Yes, that is always on my mind! Thanks.

 

[SMichelsen]

While fiddling with this, keep in mind there are lethal voltages in these switching power supplies.

Notice the point in the upper right, has a test voltage of 323V DC there.

Since we're on the topic of getting zapped while working on the power supply, is there any risk to handling one after it's been pulled from the computer? Can any elements retain a voltage after being disconnected?
In the meantime my new parts are still 4 days away. I miss my local Radio Shack!

 

[modem7]

Since we're on the topic of getting zapped while working on the power supply, is there any risk to handling one after it's been pulled from the computer? Can any elements retain a voltage after being disconnected?
In the meantime my new parts are still 4 days away. I miss my local Radio Shack!

The first section of [this] should answer your question.

 

[SMichelsen]

The first section of [this] should answer your question.

To gauge discharge status, a voltmeter/multimeter can be used to measure the DC voltage remaining on the filter capacitors.
OK thanks. But if the filter capacitor is the part that exploded and smoked up my room, is it reasonable to expect that there's no voltage in it, and therefore the power supply? Besides, it was hours between the exploding and the removing of the power supply. Having said all that, if there's a next time I will put a meter on it first...