Shugart 851 power problem

From: Bill Sudbrink <>
Date: Wed Apr 26 10:09:08 2000

> Don's observation is an astute one, since a linear supply doesn't
> generally allow both positive and negative supplies to interact.
> Unless this is a MAJOR ground loop thing, we're probably looking
> at a switcher.

Don't know how to identify a switcher, but here are the specs:
The whole box is Xerox product code F10, model 820.
The PS has a sticker which reads: ASTEC AA11860 XEROX 105P80399.
The sticker is all preprinted, that is, it does not give the
impression that those are serial numbers. The PS is one board,
with one transformer, about 1 1/2" across the windings and another,
much smaller, about 3/4" across the windings. There are three cans
about the size of AA batteries, five cans about the size of my thumb
and three smaller cans. No signs of leaks. There is a fuse marked
2 1/2 Amp, 250 Volts which seems to be in good shape. There is a
sticker which reads: "CAUTION Hazard of electric shock - heatsink
is LIVE". There are transistors and diodes attached to the sinks
and of course there are resistors and other components too numerous
to list. Nothing looks burnt, charred or popped.

> Has anybody tried powering on the drives AFTER the IMSAI box is in
> steady-state?

Here ya go:
(By the way, this is measured using the solder pads where the DC
 socket is connected to the 851 and is the same on both.)

#1 IMSAI on and booted into Cromemco RDOS, drives off:
   5 volt line reads 1.2
  -5 volt line reads 0.0
  24 volt line reads 0.6

#2 Next, turn drives on:
  Same as #1

#3 Turn IMSAI off:
   5 volt line reads 4.9
  -5 volt line reads -4.9
  24 volt line reads 23.7

#4 Turn IMSAI back on:
   5 volt line reads 5.0
  -5 volt line reads -5.0
  24 volt line reads 24.0
Received on Wed Apr 26 2000 - 10:09:08 BST

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