Shugart 851 power problem

From: Richard Erlacher <edick_at_idcomm.com>
Date: Wed Apr 26 12:33:22 2000

Well, That leaves little room for doubt . . . it's probably a switcher.
I've never seen a linear supply from ASTEC. The small transformer and small
capacitors suggest the same conclusion.

Dick

----- Original Message -----
From: Bill Sudbrink <bill_at_chipware.com>
To: <classiccmp_at_classiccmp.org>
Sent: Wednesday, April 26, 2000 9:09 AM
Subject: RE: Shugart 851 power problem


> > 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 - 12:33:22 BST