IBM PCjr Allright?????

From: Bill Girnius <>
Date: Mon Jun 23 14:02:02 1997

What am I making here? Do we know yet?
> From:
> To: Discussion re-collecting of classic computers
> 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.
Received on Mon Jun 23 1997 - 14:02:02 BST

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