Wrong capacitors for SE/30?!

[Daniël]

I've decided to recap my SE/30 today. I used tantalum capacitors, namely these for the 10x 47uF, 16V caps, and this for the single 1uF, 50V capacitor (holding off on the axials until I have a proper desolder gun, and I think the axials don't really leak much anyways).

Well, after doing it with my servicable solder skills, and ensuring everything was on solidly and all the markings were on the right side (making sure the positive side lines up with the marking on the caps as tants are marked for +), I flipped the switch and got a nasty surprise... C10 went up in flames, falling off the board. Fortunately, it seems to not have damaged anything beyond some left over soot... But why did this happen? I made sure to check the positive side... 

Are the caps for some reason not the right ones and I didn't see it? Unfortunate faulty cap? Something wonky going on with the SE/30? Honestly, if I do replace C10 with an electrolytic, I'm still rather nervous to try turning it on again...

 

[Bolle]

The caps you ordered should be suitable.

Either a bad one or you did install it backwards... I did so even though I check all caps and mark them as checked by making a little dot on them with a pen. Still managed to forget one and it blew on the first power on test.

The caps are all installed the same direction on the SE/30 logicboard - if you look at the board with the ports facing your way the positive end of all caps is on the right.

C10 connects to the +12V supply so you are operating close to the 16V limit of the cap. For tantals a rule of thumb is to use caps rated for double the voltage they will actually see.

I go for all 16V still on SE/30 boards and never had a correctly installed one explode yet but chances are that might happen sooner or later.

I would just try another cap. If it blows again go for a 25V one, but it will probably be fine.

 

[Daniël]

Given I stupidly only bought ten, I didn't have any more to check with. I stuck back on an electrolytic it originally came with, given it chimed and was audibly booting with those still installed (just no video), but it's not doing anything anymore. At least none of the other caps went up in flames. Checked them, they are all correctly installed. I'm 99% sure C10 was also installed correctly as its neighbours were, and I vividly remember checking it and seeing they were all pointing the same direction, stripe at the + on the board. Just hoping it didn't take out something else in its wake, will have to order some more caps (25V this time), and re-check the board.

 

[Paralel]

Actually fell off the board? I think that's the first time I've ever heard of that happening when a tant went up in flames. I guess it essentially desoldered itself. Interesting.

 

[Daniël]

Yep, I had the system on its side, after the capacitor lit on fire, it just fell off. Thankfully by the point it was falling to the floor it already stopped burning, but at least it wasn't falling on carpet in case it did...

Anyways, I ordered some 25V caps, will have to wait for those to arrive. Do any other caps deal with 12V? I'd like to replace those with 25Vs too. I think none of the 16V caps dealing with 5V will fail quite as horrifically as that one.

 

[Paralel]

A cap that desolders when it fails is actually a fairly interesting fail-safe. It guarantees the part that went up in flames doesn't damage the board, and it breaks the connection across it so no upstream parts are harmed by the failure.

 

[CC_333]

A cap that desolders when it fails is actually a fairly interesting fail-safe.

Do you think the cap was intentionally designed to do that? If not, I guess it is a good thing (however, one needs to be careful it doesn't pop off and hit someone in the eye; that would be a thoroughly unpleasant experience, I'd imagine.)

c

 

[Paralel]

Oh, no, it wasn't designed to do that. It just burned hot enough, fast enough, to flash melt its own solder. I was just musing on the concept, sort of like a capacitor that acts as its own fuse.

 

[Daniël]

Slow boat caps came in, replaced the exploded one, and... We got a chime, but no video. It death chime looped at first, but reseating ROM and RAM got it to at least chime. Probably UE8 on the fritz again, like my previous SE/30. 

The board did have a bit of blue funk, I guess corrosion, on it. I got some off the board "fingers" (those big contacts at the front of the board), with good scrubbing, but if anyone has a good solution for it, especially in the SIMM slots, please let me know.

 

[CC_333]

Will a failed UE8 cause complete absence of video? I thought it usually only caused the vertical line issue...

c

 

[techknight]

Yes it can if the IC fails completely. It is common. 

 

[CC_333]

Ah, OK. I wonder if I have a board or two with that problem, as I believe one will chime, but not show video (I had another that chimed and booted, but ADB was dead, so I couldn't control anything).

I came across three spares the other day, and I should see if any of them suffer from this problem.

c