http://obsolescenceguaranteed.blogspot.com/2014/03/bad-caps-or-recap-kids-apple-iie-power.html(foto's op de webpagina)
Bad Caps: Apple IIe Power Supply Repair
About a year ago I bought a fully loaded IIe for almost nothing. Despite some prejudice dating back to childhood, I found the Apple II actually very, very enjoyable! Something to do with solidity, decent expansion slots, interesting add-on hardware and very nice software. So I liked the machine... only for the power supply to develop trouble within a few days. It could only drive one expansion card. Any more load, and the power supply started clicking - no boot.
I simply bought another IIe, because strangely, that's much cheaper than buying just a spare IIe power supply off eBay. But it is not really a solution, just the addition of another machine to the collection. The first IIe looked very sad in its box (aw, puppy eyes), so I finally gave in and attempted a repair.
There is plenty of information on how to repair Apple II power supplies, and I turned out to be lucky. Mine was an Astec 240V version, and these do not need any drilling out of rivets to get to the insides. They can simply be opened by removing screws on the side.
Spotting the problem
A quick look inside delivered an immediate suspect: capacitor C13 has a bulging top. In 3D it's more obvious, but even on this picture the problem is recognisable.
But wait, there's more - RIFA filter caps on the other side of the PSU. I know these things. They spilled their guts all over my beloved Superbrain last year, my Apple Quadra still stinks of their goo, and they are now at the point of cracking up in my Mac Plus. I hate these things. They have to go, whatever principles are discussed below.
Vintage Computing repairs: the Battle Of Beliefs
Strongly held conviction, which I picked up from a couple of Grumpy Old Men with decades of real EE knowledge:
only replace parts that are broken.But then, these days the Vintage community is full of young hipsters, who feel they have to 'totally recap' any old board they put their hands on. Off go all the electrolytes, because they are all supposedly sure to be completely off-spec and waiting to explode... I think that's a hype. But try it: post a question about a stuck key on the Vintage Computer Forum, and before you know it some Recap Kid will,er, like totally recommend you to recap the board, dude. If you ask about a possible RAM error, same thing, man. Recap.
Humbug. So let's see who's right here... to the left, Grumpy Old EE with the conservative approach. To the right, Beavis and Butthead - totally recap, dude. Time for an experiment.
The scietifically robust experiment: I decided to recap the whole PSU and check the state of the removed 15 or so caps. Would they be so degraded as the Recap Kids claim they all will be after 30 years? Let's see...
An order to Farnell was quickly made - shockingly, the price for 16 medium quality caps plus shipping came out well above the price of the entire IIe. Sheesh. But it did arrive within 36 hours, which was impressive.
Fixing the board
Unsolder, remove, stick in replacement, solder. I found a most useful table with the right capacitor dimensions (here, link) so no fidgeting to put in slightly different new caps.
Removing the burst cap showed it had started to leak underneath. So even though it only bulged slightly on top, it definitely looked like the (or a) culprit.
Getting the PCB out of the case's bottom, by the way, is a bit fidgety. The DC power cable cannot (I think!) be removed from its fixing in the metal case. Instead, you have to pull loose the 240V lugs from the on/off switch, and pry the card out of the case on that end. You can then flip the board over, still with the motherboard power cable stuck on the metal casing, and do the (de)soldering.
Lucky! I put everything back together, checked the voltages and booted the Apple with added cards and floppy disks. Everything fine - finally I can enjoy Apple CP/M on the SoftCard!
Proving the Recap Kids wrong?
Yes. So what about the terrible deterioration of old electrolytes? Was their collective mass replacement justified in any way after 30 years of deterioration? Dude?
Not at all. According to my humble-but-trustworthy multimeter, they were all within 15% of original specs. Actually, even the RIFA filter caps did not show their usual slight cracks in the transparent plastic case.
So I call that 1-0 for the Grumpy Old Men versus the Recap Kids. I just wasted 15+ dollars on replacing perfectly good caps with perfectly good other caps. Listen to the experience of the classical EE types, not the Recap Kids. I like that outcome.
But, errr... look more closely at the second-last picture above. Hmmm. Maybe the score is undecided, for now. Darn. I hate it when a story develops a nuance mid-way.