Re: IIe power supply voltages

[et472@FreeNet.Carleton.CA (Michael Black)]

"Greg Andrzejewski" (pressyourluck85@yahoo.com) writes:
> Hi,
> I've been having stability problems with my IIe and suspected my "twist &
> tape" power supply mod. This led me to wonder exactly to what degree do
> voltages have to vary before you start seeing problems? Anyway here's what I
> measured with my multimeter using a HD for load.
> 
> 5v line = 5.27 V
> -5v line = -5.00 V (dead on)
> -12v line = -9.74 V (uh-oh)
> +12v line = 11.23 V
> 
Perhaps a better way to look at it is what are these powering?

The key voltages are the +5V and the +12V.  The former is used by
the motherboard and the expansion cards, obviously, and both for the
floppy drives.  

The other two voltages declined in importance.  At one point in time,
and maybe not even by the time the Apple II came along, you'd need the
-5V to power semiconductors, like early dynamic ram.  I honestly can't
think of much that would use it in the time of the Apple IIE.

The immediate thing that comes to mind for the -12V line is for
the RS-232 interface, which needs something like that voltage because
RS-232 switches between a negative voltage to a positive voltage.  I think
-9V sould still be fine, though one wonders if there is a problem with
the power supply, or simply nobody worried about it.  After all, they
do know what it's likely needed for, RS-232, and no that a precise
voltage is not important.

You can basically see the general useage of the various voltages in
the specs for the current.  The +5V will likely have the highest current
capacity, with the +12V second.  The other two will be way down in
how much current they are expected to supply.

   Michael

> I double checked the +5 and +12 lines with points on the still-connected PC
> molex connectors and they were identical to those measured through the IIe
> connector. So I hopefully can rule out any loss where I twisted and taped
> the IIe connector onto wires from the power supply.
> 
> Thoughts?
> 
> -Greg
> 
>