IBM 5155 Power supply schematics or info

16 Nov 2005

...

  I think that would be OK. While it's a bad
idea to randomly make
 adjustments, you are not doing that. You have a fairly clear idea of
 what's going on, and what that trimmer adjusts.  
 As soon as I touched the trimmer, I discover the problem !! The cursor was
 instable !!
 The outputs voltages changes only posing the screwdriver on the trimmer. 
Now yuo know why HP (and others) didn't put trimmers in their PSUs (or 
anywhere else that they could avoid). They had select-on-test resistors, 
or resistors that you clipped out to set the voltage. Typically you'd 
start with all the resistors installed (giving the minimum output 
voltage), measure that voltage and look at a table in the service manual 
that told you which resistors to cut out.

The big advantage, of course, was that you didn't get contact problems 
later on.

...
  Now, with a new trimmer (a good Beckman) the voltage
in full adjustable in
 the range.
 I have tested this power supply with various load and the regulation on 5V
 and 12V is good.

 I'm writing a web page with all your notes, my experience, photo, schematic
 and data sheets. 
All I ask is that my name remains somehow associated with the schematics.

-tony

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IBM 5155 Power supply schematics or info