[rescue] Rescued VAX 4500 question

[Stephen D. B. Wolthusen]

Hi,

On 10-Jun-2002 Tim H. wrote:
[...]
> current leakage to ground.  So how did a grounding upgrade fix the
>problem?
> 
> Oh, wait, I was thinking of ground at outlet, If your electrical code bonds
> neutral->ground at the service box, an improved building ground could help. 
> Please enlighten me, I didn't think Euro power was significantly different
> than ours in the US. (other than the obvious voltage/frequency difference)

That's more or less it. The -8/I is equipped with an unregulated (H704) power
supply, which basically means that turning it on very closely approximates a
short. The DEC installation manual is quite explicit about the 
power requirements. (you can see an image and a description of the power supply
on this model at http://www.pdp8.net/pdp8i/pics/pdp8i_powersupply.shtml. It's
not my 8/I, but maybe the -8 information is of interest to the denizens of this
list - even though these systems are of no practical value whatsoever these
days.

The original (early 50s residential) installation was never meant for this type
of load (or spike, to be more precise), obviously, and that means you get a
brief dip in the voltage. Nothing serious, but as good a reason for a heavy duty
building ground as any. 


-- 

        later,
        Stephen

Stephen Wolthusen (stephen at wolthusen.com)