7100 recapping

[mitchW]

I recently acquired a 7100 that used to crash a lot when starting. I didn't hear any cases of 7100 needing new caps, but anyway I checked them.

I then found that one silver SMD electrolytic cap has leaked (near the CPU). It was 6.3V 100uF, and I replaced it with a new tantalum.

Now the machine works like it should, but there still remain 25 more silver SMD caps on the board, however they look like brand new and show absolutely no signs of leaking, and they are all 16V 47uF. Should I replace them anyway?

 

[max1zzz]

If it where me I would probably take a selection of the 47uf's off the board to check underneath them, and if there's any sign of leakage the I would replace them all.

 

[unity]

Odds are if some are leaking, they all are or will shortly. Best to replace asap.

 

[Elfen]

The 47µf @ 16V caps are notorious for leaking. If they have not yet, they soon will. Best to recap now while the machine still works. Clean the board as best you can and then the area of each cap removed with acetone and a q-tip (cotton swab on a stick).

 

[trag]

The 7100 also commonly has overheating problems because the heat sink grease has turned to dust.  If you have not already, remove the heat sink, clean it and the CPU and reapply a small dab of fresh heat sink compound.  Do not overapply.  If the stuff runs off onto the CPU pins it can kill the CPU.  I killed a Power 120 board years ago with too much heat sink grease.  Sigh.

 

[uridium]

@Trag:

I've just re-done my 7100/80AV. It wouldn't start before. Very occasionally it'd get past the initial ram check then crater mid boot. Perhaps 1 in 15 boots, everything else resulted in the clown-funny-car-crash sound.

Recapped, regreased.. and it's booting 8.6 off an old drive like a trooper and hasn't missed a beat yet.

The caps around the audio were leaking a bit. Rest were undetectable. I suppose they'd simply dried out.

Good luck!

 

[uniserver]

i just had a customer send me a g3-233 beige that has leaking tin cans...  sigh... but you know trag or someone was saying that there has been 68k macs that have needed caps since 1997-8 ish... i think... so yeah its time folks!

 

[trag]

i just had a customer send me a g3-233 beige that has leaking tin cans...  sigh... but you know trag or someone was saying that there has been 68k macs that have needed caps since 1997-8 ish... i think... so yeah its time folks!

My first non-compact, a used IIci, stopped working while I was in that little apartment on 38 1/2 St. So that had to be '97 or earlier. Searching turned up a post in the comp.sys.mac.*** news groups (where we used to do what we do here) which discussed bad caps and MB damage. Mine had a ruined via and the traces to it were iffy. Bypassed with wire wrap (and replaced the caps, of course) and used the IIci for several more years.

 

[asaggynoodle]

Just a note for anyone interested, I've learned that if you dip all of your Capacitors in Conformal Coating, unless they explode, you should never have to worry about it leaking all over the board again. 

Conformal Coating is a Clear Nail Polish like liquid that is intended to be applied on PCB's to prevent shorts or failures due to condensation and improve reliability. But, should be usable either to dunk the capacitors, so they are basically super sealed and the fluid is contained, or even doing a circle around the bottom of the cap on so the leaking only lands on the Conformal Coating and not the Traces below.

In commercial production, it can even be used to cover the entire boards.. I mean if you're going through the trouble to change all the caps, for ~$11 you could guarantee the board will never be destroyed by a bad cap again.

 

[CC_333]

This would be good for museum pieces, as it would preserve them forever.

For daily use, though, I worry because what happens if a chip dies? Can this stuff be somehow removed (easily) to allow for such repairs?

c

 

[MidnightCommando]

Conformal coating can typically be removed chemically, should replacement of components later be required. 

There's a guide on it here for the interested. 

 

[raoulduke]

I'll acknowledge I only skimmed this and it's sort of off-topic; is there a cap list for the 7100?  I had trouble finding one when I looked last month.

 

[raoulduke]

Are there only 25 16V 47uF?  Nothing else on the 7100 board?

 

[uridium]

The coating looks not to nasty to remove.

Anyone actually applied this stuff then needed to do some solder re-work afterwards successfully? I'm curious as to how hard it is in reality beyond the sales pitch. Anyone?