23 Jun
1997
23 Jun
'97
7:02 a.m.
What am I making here? Do we know yet?
----------
From: jpero(a)mail.cgo.wave.ca
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Subject: Re: IBM PCjr
Date: Monday, June 23, 1997 9:51 AM
Hello Tony,
>
> >From memory the central pin is chassis ground and the outside 2 are
18V
AC
at about 3A.
Actually 34vac 2amp center tapped transformer. The center tap goes
to ground, what else how can negative voltages can be generated so
it needs this ground. The both outside 2 pins for 17v ac lines goes
there. The card rectify it to generate 3 dc voltages, two is
positive and other one is negative. Bulk of the components is used
to generate 5vdc, and a wimpy 12vdc source for the floppy drive and
fan. And last one is in very small current negative current -12v dc
which takes this voltage and go through a 7905 regulator to get -5v
dc, both voltages are strictly for serial use and little use for
else.
Funny, instead of 60hz, you get the same type of circuit design in
secondary side in lots of switching power supplies with few minor
differences.
The limits to overdrive if you do, both card and slot is due to the
current limit allowance per contact on that slot. :( Leave it to be
and parallel the seperate power sources to the sidecars if they have
them. Another problem with this is that 3 connections is not enough
to carry more than 2amp on each socket.
By the way, I am Electomechanical major in training "on hold". :)
The manual doesn't give the schematics of the
transformer unit (it does
for the PSU card in the main unit), and it's not clear from the
description whether the AC input is centre-tapped to ground or not.
Looking at the schematics, I think that it is _NOT_
Oh yes, I did saw the techref for the outside PSU transformer is
pretty simple just a disconnectable center tapped transformer.
One thing I hated that they did not give us the that schematics for
that power card module which I revsere engineered instead!
Jason D.