Help resurrect my Xerox Alto

Tony Duell ard at
Mon Sep 13 15:26:02 CDT 2010

>   I thought a video might be easier for you all to see the issue I am 
> having with restoring my Xerox Alto.
> The issue I am having is the Diablo Disk drive does not power on fully 
> (I am measuring +15 and -15V on the drive, but +5V is only measuring at 
> around 2.5V.  The lamps on the front of the drive do not light-up, and 
> the LOAD/RUN button does nothing, hence the door lock does not unlock.

I don't know the Alto at all, but this sounds a bit like a Diablo model 
30 drive. In it?

If so, from whta I remember, it derrives the +5V rail intenrally from the 
+15V supply. If the +5V rail is low, then either there's a problem in the 
regulator, or an overcurrnet condition (maybe a nearly-shorted 

FWIW, I have the DIablo Model 30 service mnaual, but it woudl take a 
little time to find it.

> Here is a link to the video:
> I have visually inspected all PCB boards and components, nothing seem to 
> be damaged.  Also, the power supplies seem to be outputting power 
> properly (as seen via the RED voltage LEDS in the Alto card cage.

I would still chekc thiem with a voltmeter and a 'scope (to look for 
excessive ripple).
> Any recommendations on how to troubleshoot the disk drive further?


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