Help resurrect my Xerox Alto

[Tony Duell]

> 
>   Al,
> 
>      Do you know which board/component inside the Alto creates 5V from 
> the incoming 15V?  If you can describe it in detail, it will help me 
> immensely (so I can diagnose the failed component).

I beleive it's a circuit (more than one component is involved) inside the 
Diablo drive. Certainly the Model 30s I used on a PDP11 only took +/-15V 
from the PSU.

You need to get the service manual for the deive (Eric Smith suggested 
there's something of use on bitsavers) and see how the 5V is produced.

Note that the fault may well not be in that section. It's entirely 
possible for excessive loading (say a very leay capacitor) to pull the 
output of the regualtor cirucit down so that it can't supply 5V properly. 
Before you start replacing parts you, as ever, need to do some tests 
(Yes, I know this is not the way it's done these days, but it's the way i 
do it, and it's never failed me...)

-tony