From: jpero(a)mail.cgo.wave.ca 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

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". :) 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.