New Capacitor Blew Up

[Mike Richardson]

In the process of re-capping an SE/30 board. I did 2 caps yesterday without any problems, it tested fine. I did 4 caps and ran out and decided to test the progress so far.

Plugged it in, turned it on. First few times I got the corrupted screen so I just turned it off and on a few more times until I got the correct grey screen (this worked before to get it to boot sometimes when I just had the 2 caps replaced. Nothing got it to boot with no caps replaced though. I think the cap near the ROM is integral.)

I got the grey screen for a few seconds and then POP one of the new caps blew it's top and vented. It's one of the caps near the power connector.

My theories are:

1. Bad new cap.

2. I did it wrong (I got the + on the right side and didn't lift a trace, that's as good as it gets for me)

3. I need to replace all the caps, before powering it on. Although I did my LC II board one at a time, one cap, then test, one cap, then test, and that worked fine.

 

[tomlee59]

It's either 1) or 2). If the other caps are bad, they won't cause a new, good one to blow.

The most likely thing is a reversed-polarity cap. That will rapidly cause poppage. Much less likely, but not impossible, is a defective new cap (assuming that the voltage rating is correct).

 

[Mike Richardson]

It was 2). I put every cap on backwards. I had forgotten how they went on. Damnit!!!

I just fixed all of them now. I also did one axial - I think those are harder than the surface mount, a lot harder to get out and put in the new one. They don't seem to be leaking, but I just bought a huge lot of like 500 capacitors and had some of them put in as well for preemptive replacement.

This SE/30 board should be done shortly and that should get one of my compacts working again.

 

[JDW]

I've been working with electronic devices since the late 1980's. During all these years, and yes I still work with electronics, I've never come across a "bad new cap." Seriously. I've had caps go bad over time and blow because of reversed polarity. But I've not seen a bad one come off the assembly line. Statistically "bad caps" must exist. But I've never seen one first hand.

Human error is the culprit the vast majority of the time.

 

[Mike Richardson]

I hate axials!

I only have one cap left and it's the other axial. One side came out fine. The other side kind of broke off and left a tiny little piece of metal in the hole.

No matter what I do I cannot get this to heat up and get the little piece of metal to come out, I hold it on there for a full minute, I tried more heat, I tried either side, etc. It won't budge.

 

[Dennis Nedry]

I hate axials!
I only have one cap left and it's the other axial. One side came out fine. The other side kind of broke off and left a tiny little piece of metal in the hole.

No matter what I do I cannot get this to heat up and get the little piece of metal to come out, I hold it on there for a full minute, I tried more heat, I tried either side, etc. It won't budge.

Are you using a low-power iron? It may be time to crack out the big one. Hang onto the piece with a needle-nose, heat it up on the opposite side of the board, and it should slip right out of there.

 

[Mike Richardson]

I hate axials!
I only have one cap left and it's the other axial. One side came out fine. The other side kind of broke off and left a tiny little piece of metal in the hole.

No matter what I do I cannot get this to heat up and get the little piece of metal to come out, I hold it on there for a full minute, I tried more heat, I tried either side, etc. It won't budge.

Are you using a low-power iron? It may be time to crack out the big one. Hang onto the piece with a needle-nose, heat it up on the opposite side of the board, and it should slip right out of there.

It's an adjustable iron so you can go from 5W to 40W. I was running it at 40W and it still wasn't helping. Maybe it's defective and not really going at 40W.

 

[tomlee59]

I hate axials!
I only have one cap left and it's the other axial. One side came out fine. The other side kind of broke off and left a tiny little piece of metal in the hole.

No matter what I do I cannot get this to heat up and get the little piece of metal to come out, I hold it on there for a full minute, I tried more heat, I tried either side, etc. It won't budge.

Then leave it in. Discretion is definitely the better part of valor here -- you may ruin your board by persisting. There's no harm in having a short pigtail in there. Indeed, I wouldn't even try to install a cap there, if it's truly a bypass cap. There are more than enough to tolerate the absence of one or two (or several). Just leave it be.

 

[Mike Richardson]

I managed to heat it up on one side, and pull the tiny nub out on the other side, and get the new axial installed. I don't know what the big axials do on these boards. They are 220uf and 470uf, 16V.

It's booting up off the floppy just fine! Looks like a success!

Except this is an SE/30 board in an SE and with the big new cap near the ROM it no longer slides all the way into the SE. But the SE/30 made it's chime and has nice strong sound and boots up right away.

 

[tomlee59]

Congrats, Mike, on successfully completing the repair. Another one saved from the bin...