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Old 6th March 2012, 7:58 PM   #1
aXLe Thread Starter
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Default Re-capping an Apple ][ PSU

Over the years I've owned a number of Apple ][ computers including a ][ europlus and a number of //e's.

More often than not, if the power supply hasn't failed already (due to age), then it does shortly after it is fired up. Generally I've found it to be the AC capacitors that fail - spectacularly with a fizzing sound and a bit of horrible smelling smoke. Generally most of the psu's I've come across have fired up fine once re-capped - these would have been psu's that worked fine when the unit was put into storage.

After 25 years it's not surprising, and you may find many of the electrolytic caps are also starting to vent and leak either from the top (obvious), or from the bottom.

So in this thread I'll go through the process of re-capping the psu, with lots of photos.

WARNING : This power supply has very high voltages present when powered, and some of the large capacitors will hold significant voltage when the unit is off. Some of the heatsinks may be live when the PSU is operating - do not operate the PSU without the cover fitted.

Here we have a typical Apple //e PSU - removed from the case :



Under the cover we see the electrolytics and AC caps that we will be replacing :





So we remove the PCB from the bottom of the aluminium case, and start the process of removing all the capacitors that we will be replacing. Note the polarity of the electrolytic capacitors is clearly marked on the PCB:







The old caps :



Failure quite visible on this AC cap :



Next we have to source suitable replacements. The caps should be low ESR, high temperature caps, and of a good quality.

I've been buying the Hitano capacitors from Worldwide Electronics in WA. I put together this spreadsheet with old caps versus suitable replacements :





One thing to be aware of is that the modern day replacements are far smaller in physical size that the old ones.



This can cause complications with the lead (leg) spacing required to fit the new ones to the original PCB. Apple provided a couple of alternative lead spacings on the PCB for the AC caps and some of the electro's, but for the large electroytics it is neccessary to bend the legs out such that the lead spacing is correct for the PCB :




New caps fitted :









Board back in the case :






Job Done!

My Apple ][ Thread here

Last edited by aXLe; 1st May 2012 at 8:51 PM.
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Old 6th March 2012, 8:34 PM   #2
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nice guide

i wish i understood how PSU worked and why capacitors are so fundamental to their operation!
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Old 15th March 2012, 4:04 PM   #3
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I'm surprised how new and clean the PSU's look for being around nearly 30 years old!
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Old 16th March 2012, 7:05 PM   #4
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i would think being a passively cooled and sealed unit would help a little.
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Old 16th March 2012, 7:46 PM   #5
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One way to get around the smaller size is to use caps with higher voltage ratings. That way the fit straight in and you have more overhead for longer life.


Also, did you glue the caps in at all? Might be worth dabbing a bit of hot melt glue or silicone around to prevent stress fractures on the legs of the caps.
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Old 29th March 2012, 1:29 PM   #6
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Quote:
Originally Posted by Paronga View Post
nice guide

i wish i understood how PSU worked and why capacitors are so fundamental to their operation!
AC power goes up and down in a sine wave, when you try to straighten that out to low voltage DC you still have bumps and an on-off pattern. Capacitors store up some of the power when the voltage is high, and let it go when the voltage is low, thus buffering/smoothing out the voltage.

That's also why LEDs on monitors etc. stay on for a few seconds after pulling the power, and why it's dangerous to work on things like PSUs and TVs even when they're unplugged.
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Old 2nd April 2012, 7:08 AM   #7
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Very nice power supply love the old school design. Would be a little warm in there but surprisingly quite good for its age as the heatshrink on the electrolyics haven't pulled back that much. Thats what you get with real Nippon capacitors instead of Chinese crap
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Last edited by aokman; 2nd April 2012 at 7:13 AM.
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Old 4th May 2012, 10:33 AM   #8
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Great guide, cheers. The size difference in the new caps is always interesting to see, especially on the 16v 330.
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Old 18th May 2012, 10:34 PM   #9
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Nice writeup. Those X2 supression caps really need replacing. I just did the same with a *couple* of my apple II and IIgs psus. Though I used Panasonic TS-UP, FC and AM series caps for the electrolytics (I have a small vintage audio gear business so I get them regularly for customer jobs).


photo-14 by , on Flickr

Just like a nice stack of pancakes. Apple II power supply pancakes!
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Old 28th November 2012, 9:43 PM   #10
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Default It works!

A quick thank you to aXLe.

I had a problem with a IIe I bought on eBay. Looking at the voltage outputs the 5V lines were low, and the 12V ones non existant. Then suddenly as I was probing they all came alive! But alas trying again later I got the same results. So there was something wrong.

Looking for the schematics I couldn't find the exact one. Only a US model which has some differencies to this. Probing around again I could see that essentially there was signals everywhere, so nothing seemed failed that I could see. Or certainly not completely failed. Making it one of the worst types of failure to find. Then I found this forum post.

I was 50/50 on if this would work, but considered it would rule out some of the doubt over those components. Then it would give me a clearer indictaion that the problem was elsewhere. However, after changing all the caps as directed above everything started working again. The feedback waveforms that I monitored before were now about a fifth the frequency they were. So the caps certainly made a difference.

I did find that a company is selling replacement PSUs on eBay:
http://www.ebay.co.uk/itm/3210273704...84.m1438.l2649
Being sold by the company:
http://www.atlaz.com/

Thanks again!
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Old 29th November 2012, 10:06 AM   #11
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good to hear - hopefully your machine will now run for many years to come :-)
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Old 4th March 2016, 12:35 PM   #12
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Thanks for the info on the parts listing. Just got myself an apple 2e and on first boot the power supply fried.

Just followed your parts list in the spreadsheet and ordered from the same place, hopefully I should have the parts soon and I'll see what happens from there.

Cheers
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Old 4th March 2016, 1:59 PM   #13
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Quote:
Originally Posted by Paronga View Post
nice guide

i wish i understood how PSU worked and why capacitors are so fundamental to their operation!
https://www.youtube.com/watch?v=Z6An-IRTQbo
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Old 4th March 2016, 8:51 PM   #14
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Quote:
Originally Posted by CAESAR View Post
Thanks for the info on the parts listing. Just got myself an apple 2e and on first boot the power supply fried.

Just followed your parts list in the spreadsheet and ordered from the same place, hopefully I should have the parts soon and I'll see what happens from there.

Cheers
Good stuff
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Old 25th March 2016, 10:59 PM   #15
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Finally had a chance to recap the power supply. good news is that it fires up but the bad is that the voltages are down so not sure where to go from here.

+5
-4.7
+11.5
-10.93
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