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Re: Apple Power Supply Questions

capknight wrote:

On Apr 13, 3:44 am, "Michael J. Mahon" <mjma...@aol.com> wrote:

capknight wrote:

On Apr 12, 7:39 pm, capknight <cepheusfi...@gmail.com> wrote:

Hello,
I picked up a number of active and dead power supplies recently. A few
are the AE Vulcan GS supplies, AE IIe Supplies and original OEM Apple
supplies.
Some were dead but I was able to resurrect them by replacing the
electrolytic capacitors.

Yes, I have a couple of supplies to do the same surgery on.  ;-)


The readings are a bit odd on the Vulcan GS supplies. I've listed them
below with modified and unmodified numbers (meaning I replaced the
caps in one and left the other original).
The negative 12 volt leg seems really low on the Vulcan GS supplies as
well as the re-capped AE IIe supply.

Since I presume these are unloaded voltages, they are solely the result
of inaccuracies in the windings of the high frequency transformer.

The voltages you report are all within tolerances for the uses that
the supplies are intended for.


I did not test the Vulcan GS supplies with the 105mb hard drives
installed. I was able to find re-certified drives that work just fine
with the Vulcan GS cards.

I'm curious about which drives you found that work...


Testing was done straight from the boards and not through the cables.
One thing I did note on the Vulcan GS supplies is that the gauge of
the wires from the 120v receptacle to the switch and board are very
thin in comparison with the other supplies.
Any thoughts?

That shouldn't make any difference.  The total power drawn by the supply
is well under 100W, so the line current is under 1 ampere.  Any slight
voltage drop in the line section is regulated out by the supply.




Thanks!
C
Modified Vulcan GS (caps replaced):
================
-4.32
-10.07
+12.19
+5.47
Fan: +12.17
Molex for HD:  (red) +5.46
                   (yellow) +12.17
Unmodified Vulcan GS:
==================
-4.27
-10.05
+12.13
+5.42
Fan: +12.11
Molex for HD:  (red) +5.47
                   (yellow) +12.08
Modified Applied Engineering IIe Supply (caps replaced):
============================================
-4.99
-11.6
+12.03
+5.28
Unmodified Apple IIgs Supply:
=======================
-4.98
-12.13
+11.24
+5.05

I forgot to note that I did make some slight adjustments to the pot on
the board to see if I could move the voltages around a bit. It helped
on the AE IIe supply.
Thanks,

The only actively regulated output is the +5v--all the other voltages
are supposed to track that voltage open loop, just by virtue of the
transformer winding ratios.  The adjustment is for the +5.

Standard Vcc tolerance for TTL is 5v +/- 10%, so anything from 4.5v
to 5.5v is within spec (though timing margins will vary somewhat
over that range, the parts should continue to meet spec).

The other voltages are less critical, particularly the negative
voltages.

-michael

******** Note new website URL ********

NadaNet and AppleCrate II for Apple II parallel computing!
Home page:  http://home.comcast.net/~mjmahon/

"The wastebasket is our most important design
tool--and it's seriously underused."


Thanks for the reply!

Perhaps I should also try the supplies under load. I was mostly
concerned by the odd readings in the Vulcan GS supplies on the
negative voltages.


The negative supplies are used by only a few circuits, and only
for bias, with very low currents.  I'd expect everything to work
fine with a 20% voltage tolerance.  The only exception would be
circuits that were marginal to begin with, but again, I don't
expect any problems.

The loads I use are 25W wirewound resistors.  I use a 5 ohm load
for +5 (1 ampere) and a 10 ohm load for the +12 (1.2 amperes).
This is actually a "disk busy" load, so it gives a good indication
of the supply's performance.

Negative voltages don't require loads, since only a few milliamperes
are drawn from them in use.


I have much to learn about these things. At the moment I was just
comparing the existing caps in the supplies, matching them as close as
possible on Digikey and installing. It's actually worked out pretty
well so far!


Great!  You might also want to compare Jameco for prices.

<snip>


Henry over at Reactivemicro dug up a IIe ROM for the Vulcan card so I
can put one of them in my IIe. I need to do some research to make sure
the Vulcan GS and IIE card were the same except for the bios (crossing
fingers).


That's correct.


I have/had a third Vulcan GS card and supply, but I made a boo boo on
the supply and it was quite the spark. The card is misbehaving from a
different mishap.


The current surge may have only blown the fuse.  The supply may be
otherwise undamaged assuming that the short has been removed.

Unless the power transistor is blown, it shouldn't be too hard to
fix.  The problem with switching supplies, apart from the fact that
they are dangerous to probe while operating, is that they are
regulated by a feedback loop.  Anything amiss in the loop can cause
misbehavior (like shutdowns), so there are more components to rule
out than if the feedback loop were not there.

One way to simplify diagnosis of a feedback system is to break the
loop, so all "signal" flows are one-way, but many systems are unstable
with the feedback disabled, including most switching supplies.


Two functional and one down. Ack.

Anyhow thanks again for all the info!


You're welcome, and good luck!

-michael

******** Note new website URL ********

NadaNet and AppleCrate II for Apple II parallel computing!
Home page:  http://home.comcast.net/~mjmahon/

"The wastebasket is our most important design
tool--and it's seriously underused."