IBM 5155 Power supply schematics or info

[Tony Duell]

> 
> > I traced out scheamtics of the PSUs in all my IBMs...
> 
> Great work ! Normally I trace out schematics only when I need to repaire its
> and I cannot find any schematics on the net.

Oh, I like to understand how things work _while they're still working_. 
Then if I need to make any measurements on th working device (even 
something as trivial as determining if a house-coded transsitor is NPN or 
PNP), I can do it knowing the componnent is good. 

Of course this is not always possible (e.g. when I'm given a non-working 
machine).

> 
> > How quickly do you need this? I am wondering if handing a copy to a
> > friend at an HPCC meeting in a couple of weeks time would be soon enough.
> 
> No problem for the time, it's a hobby (great but hobby) non work :)

OK, pester me a little before the meeting (12th Nov) and I'll take a copy 
along.

> 
> > Yes, and the control chip is on the 'output' side of the PSU, the drive
> > to the bases of the chopper transistors is transformer-coupled. There are
> > 3 little daughterboards in there.
> 
> I have take a look at the circuit. It' similar to some off line converters
> and other supplies, with control on the secondary side and not in the "live"
> part of the switch mode.

Yes, there's nothing particularly odd about it.

> 
> > One is an inrush limiter and contains a
> > relay that shorts out a power resistor once the smoothing capacitors have
> > charged.
> 
> This work, I've tested. The 4 ohm resistor is shorted correctly by the relay

OK.

> 
> > Another contains the overcurrent protection circuit, and, IIRC,
> > a 12V regulator. The last contains the overvoltage protection circuit
> > (the chips on that board are LM339 quad comparators).
> 
> I'm thinking about some protection circuit, because the switching try to
> startup, for a time less then half second, and then stop. Now I can try to

There are 2 protection circuits. One is a current sensor, there's a 
current transformer in series with the chopper transformer primary 
winding. The other is a set of voltage sensors.

Whatever you do, don't disable any of the trips. If there really is 
something wrong, the results would be spectacular!.

> check il any protection become active during startup.
> The SG3524 il correctly powered and try to fire up the switching
> transistors, via the pulse transformer, but only for a short time.

Do you get any voltage appearing on any of the outputs? Even for that 
half-second?


-tony