Retrochallenge meets WOzFest – Check Your Caps!

Apple II Europlus
Apple II Europlus

Retrochallenge 2017/04 is almost over!

WOzFest PR#6 has now started!

It’s time for the two parts of my retrocomputing life to collide in the most resourceful of ways…

My “europlus Refurbapalooza”, whereby I’m trying to get all my europluses operational, has been the thrust of my two Retrochallenge entries in 2016/10 and 2017/04. With the vagaries of “real life” impinging more the second time around (just that time of year, I think), I’ve gotten even less done this month…but that doesn’t mean I’ve been entirely unproductive.

I’ve been able to test the electrolytic capacitors in all seven of my europlus Astec AA11040C power supply units (PSUs). Despite 14 electrolytic capacitors per PSU (so 98 total) and the PSUs being at least 35 years old, I was pleased to find only four capacitors are exceeding (or almost exceeding) their maximum ESR (Electrical Series Resistance) value.

I’m also going to follow the general guideline to replace the C1 filter capacitor, even if the original hasn’t blown (two of the seven originals have definitely blown, and a further three or four are showing cracking in their plastic covering). I’ve bought all the replacement capacitors I need, and hope to install them all and test the PSUs during WOzFest PR#6.

While carrying out these ESR tests, I wanted a ready-reference to the capacitor specifications for determining the correct ESR value to be testing and for when I came to purchase replacement capacitors.

As a non-expert, I also wanted a reference to the position and polarity of the solder points for each capacitor on the underside of the PSU circuit board – I was testing the capacitors “in-circuit” rather than removing them for testing (while not ideal, I’m trying to keep the task manageable).

I had found online a scan of a 1982 document from Apple which provided a great start to what I wanted. It has schematics and circuit board layouts for several Apple PSUs, as well as a components list for each of the PSU models it includes.

Although it has info on the AA11040B (while I have AA11040Cs), upon inspection I believe the primary difference is the AA11040C is the 230V version of the AA11040B with the “115V Select” wire removed and a 250V/2A fuse replacing the 125V/2.75A fuse.

So I decided to prepare just the sort of ready-reference I would have liked to have started with. Over several iterations to refine the design and info included, and taking input from enthusiasts with more PSU repair experience than me, (thanks Mark, Martin, Jon, Geoff and John!), I’ve created the “WOzFest Labs Apple Astec Power Supply Unit AA11040B/C Electrolytic Capacitor ‘Spec & Check’ Sheet” (it just rolls of the tongue!) – and I’m pleased to announce the release of v1.0 of this “Spec & Check” sheet for use by other enthusiasts looking to test and refurbish their AA11040B/C PSUs.

This release is the major result of my Retrochallenge 2017/04 entry and in line with WOzFest PR#6’s theme of “Preservation”.

I’ve designed the sheet so that it can be printed at 100% on A4 (297✕210mm) or US Letter (8.5″✕11″) without any information being cropped. When printed at 100%, the picture of the underside of the PSU circuit board is “life size”, so it’s easy to correlate the highlighted solder points to a physical circuit board.

The sheet can be used as a checklist of capacitors that are in or out of spec, has the maximum ESR values listed for each capacitor (as well as other specs) in both tabular and “call out” forms, and the polarity of the solder points are annotated and colour-coded.

This is only v1.0, and suggestions/corrections from other enthusiasts will be included in updates. If I’m able, I’ll also release versions for other PSU models that Apple used in Apple ][s.

This is the first resource issued under the name “WOzFest Labs”, and hopefully there’ll be many more (I’ll probably re-release my Silentype Font under that name, too). I’d be interested in collaborating on other resources, too, so hit me up if you have any ideas you”d like to work on with me.

A few notes:

  • I’ve provided specs and solder points for the C1 filter cap to ease replacement of this component along with any out-of-spec electrolytic capacitors;
  • Capacitors C13 and C14 are in parallel on the circuit, so testing either one to half the usual maximum ESR is adequate when testing them “in-circuit” – if capacitors are removed for testing, double the stated maximum ESR value for these two capacitors;
  • Capacitors rated to 105°C are recommended;
  • The 1982 document from Apple has at least two errors in the components list for the AA11040B PSU, so check its information carefully if you’re using it as a reference.
  • If you’re wondering about the typewriter-like font I used, it’s Prestige Elite, which, by my reckoning, is the font used in early Apple spiral-bound manuals such as The Applesoft Tutorial. It’s my theory that these early manuals were “typeset” using material printed by the ubiquitous IBM Selectric typewriter.

So, other than some soldering, testing and writing a recap on my re-capping adventures, that’s pretty well it for my Retrochallenge entry this time around. I’m looking forward to getting to the meat of my europlus refurbishment – testing (and hopefully repairing) motherboards – next go ’round in October!


This post was originally published on this site.