Quadram Quadboard 1982 battery replacement

[dhau]

I bough an IBM PC 5150, and inside it had two Quadram Quadboards from 1982. Both had their rechargeable batteries already removed. I'd like to add coin CR2032 batteries to those boards. Did anyone do it before?



As I understand, I have to put a diode in series with the battery to prevent charging current from messing with the battery. Also, if I understand it right, when the card is powered from the power supply, diode is cutting off the battery, so it doesn't discharge while PC is on. To prevent a significant drop in voltage, I should use a schottky diode like 1n4001, not a zenner diode like 1n914. I should also have a 100 Ohm resistance in series with battery and diode, as per OKI MSM5832 datasheet. Fortunately there is already a 100Ohm resistance between battery plus and chip Vcc pin.

Any advise or experience is very welcome!

 

[Chuck(G)]

Also, if I understand it right, when the card is powered from the power supply, diode is cutting off the battery, so it doesn't discharge while PC is on.

Not quite--the diode is there to prevent the PC from attempting to charge a primary (i.e. lithium coin cell) battery when the PC is on. Very bad when that happens with lithium ion batteries.

A 1N4001 is an ordinary silicon rectifier, with a bandgap of about 0.6-0.7 volts. A schottky diode for this application is a 1N5817--which will give you a voltage drop of about 0.3V.

 

[dhau]

I replaced battery on my 1984 model of Quadram Quadboard: photos and prose. I'll try to test it ASAP. Hope it works.

The two 1982 model Quadboards in first post don't work at all, so I have to figure out why.