A cap fell off my SE/30 Motherboard.

[brayne]

Hi all,

I had my SE/30 open today to replace the PRAM battery, and to try and work out why it wasn't producing any sound (I was guessing that the speaker cable wasn't connected).

Anyhow, I opened it up, and while carefully removing the motherboard (a job I have undertaken on many an occasion) a capacitor fell off.

Given the level of corrosion under it, and how easily it fell off, I'm guessing that it hasn't been making proper contact for some time. To my surprise, the Mac boots and operates perfectly (still no sound though).

Can a guru out there possibly enlighten me and tell me:

a) What purpose this component serves, and how come the Mac still works without it?

B) If it will pose a long term problem by not being there?

c) If I have to replace it, are these capacitors available?

d) Is this likely to happen with the other capacitors of the same type on the motherboard?

I've attached a pic so that you can see where it came from (C13, just near the PDS).

Many thanks in advance,

brayne

 

[Unknown_K]

Leaky cap. Clean the junk off of the solder, then remove the old solder, solder on a new capacitor.

 

[Mk.558]

You should remove the other capacitors and clean the board immediately to prevent further damage.

Unfortunately such is the state of many, many SE/30s in the wild.

The capacitor in question is a certain C13, which is a power decoupler for the +5V supply feed. It is quite important, and there are a few other 47µF capacitors that filter the power from Pin 12 of Port J12.

See the first link in my signature for more.

 

[Unknown_K]

Yes, replacing all those aluminum surface mount caps is the best way to deal with it (it is what I did on my SE/30's), but most people just fix the most pressing issues and deal with the rest later if ever.

 

[Juror22]

I had gotten an SE/30 recently and it started up perfectly, other than it seemed to have a dead battery (kept losing its settings). I thought that perhaps I had one that was an exception, since it was running perfectly and from looking at the caps (without removing the system board), they appeared to be ok.

When I removed the board to change out the battery, I saw where there were almost unnoticeable slicks of capacitor leakage, I had caught it just in time. I cleaned the board, replaced the caps, the battery, cleaned and re-lubricated the floppy drive, put it all back together and played Maelstrom on it (external color monitor, since it has a video card).

Retro-fun! :beige:

The moral of this story is that replacing the caps is not an option if you enjoy using your aging SE/30.

There are differing opinions on how to do it, but I agree with the consensus that it has to be done as soon as possible on any remaining SE/30's.

 

[brayne]

Thanks everyone, that's fantastic info.

So I guess the next question is, what do I replace them with? Can someone recommend particular caps that will last better than the originals? I'm guessing this has been covered elsewhere in this forum in the past.

Thanks again,

brayne

[edit] Sorry folks, ignore that last request. I just found the relevant thread in the Trading Post section.

 

[Mk.558]

Technically speaking, electrolytic replacements would be better as far as the original design goes - they did have tantalum capacitors back in the day and chose not to use them (one reason could have been cost), tantalums can fail through internal short circuiting. When they do it is a violent POP!!

They are also a lot harder to solder on to the board than radial electrolytic replacements.

 

[JDW]

...what do I replace them with? Can someone recommend particular caps that will last better than the originals?

The Trading Post info is here:

viewtopic.php?f=4&t=16626

Further info on capacitor replacement:

http://68kmla.org/wiki/Capacitor_Replacement