Re: Apple Power Supply Questions

[capknight <cepheusfilms@gmail.com>]

Hello!


 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.

Sweet! Any additional info is much appreciated.

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

Definitely will check them out too!

> > 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.

So the cards are the same and the bios is just different? Exciting!

> > 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.
>

I think I nuked the power transistor. The Vulcan has those somewhat
"interesting" heat sink attachments to press the transistors against
the wall of the supply to conduct their heat. The piece of aluminum
holding that particular transistor (I am guess that's the one right
next
to the fuse assembly) is a bit tarnished. When I replaced the fuse and
tried again, the spark comes right out of the area.

Ack.

I think it has to do with the ceramic caps I replaced. The two ceramic
caps that look like little boxes. Think I read the readings
incorrectly
and installed incorrect replacements. Oops.

Somehow I lost the two originals as well (ack).

Need to figure out what to replace now.

Keep me busy this weekend! In between blowing power supplies and
running all my cases through a bath of retr0bright! Hah!

Thanks again!

C