IBM 5110 power supply schematics?

Mattis Lind mattislind at
Tue Oct 8 11:32:10 CDT 2019

It turned out my friend was wrong. The power transformer is most likely ok.
But one of the main choppers were short circuited (yes, it is a switcher,
again to little info from my friend).

Anyway. The chopper transistors were TI made in 1978 but marked T484.
Probably some IBM marking which no one has the cross for.

I replaced them with nice high voltage high current TO3 transistors The
only thing i could get from the original transistors except for the
physical appearance was the polarity.

With a 5.6 ohm resistor on the 5V i fired up the PSU with a 60W lamp in
series with one of the mains leads. Nothing happened on the bases of the
switchers until I got to around 190 VAC input.
At that point the base went high and stayed there.

Really strange. Of course I have no schematics for this IBM thingie. Does
anyone have a schematic for the IBM 5110 PSU? I think I really need it to
understand what is going on.

Tracing it out is an option but then all those square metal canned IBM


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