Subject: Re: US vs European PS requirements.
To: NetBSD/vax Mailing List <port-vax@NetBSD.ORG>
From: Geoff Roberts <>
List: port-vax
Date: 06/01/1998 11:01:11
-----Original Message-----
From: Jacob Suter <>
To: Brian D Chase <>
Cc: NetBSD/vax Mailing List <port-vax@NetBSD.ORG>
Date: Sunday, 31 May 1998 17:19
Subject: Re: US vs European PS requirements.

>> I have the PS of a VS3100/M38 "extracted" from the case here in front of
>> me and I don't see any explicit way to switch it over to accepting
>> different input voltages.  Would the PS need to be replaced, or is the
>> thing just smart about how it handles the different input voltages?
>Two possabilities -
>A> It'll just accept it (This *IS* DEC we're talking about, so probably

I have a VS3100/M30 here that is 240vac.

The psu is type H7821-00 and is labelled as follows:-

 V ~100-120/220-240  Hz 50-60
 A 2.8/1.5   W 180

I translate this as being a dual voltage supply, but there is no (visible)

I see no voltage changeover switch ala IBM PC style on it anywhere, it's
either internal or the supply is voltage sensing, which is not uncommon in
switch mode supplies of this nature.

>B> You'll have to change the coil tap on the primary step down
>transformer in the power supply, if there even is one.

I think you'll find it uses a mains rectifier followed by switching circuit,
there is no mains transformer as such in switch mode power supplies.

>except for cases when line frequency is an issue (most of the world uses 50
>we (Being US/Canada/Japan (Mexico?) use 60 hz.  In the case of computer
>power supplies I have never heard this to be a problem,

Frequency of the mains is not a real issue, as it is rectified to DC and
filtered before it is fed to the switchmode circuitry.

>I really do think my 3100M30 has a 220/110 switch on it, but its been a
>few weeks since I looked at one so I'm probably wrong.

Mine doesn't seem to, might rip it out and have a closer look.

Hope this helps

Geoff Roberts
Computer Systems Manager
Saint Marks College
Port Pirie  South Australia.
My ICQ# is 1970476
Ph.  61-411-623-978 (Mobile)
       61-8-8633-0619 (Home)
       61-8-8633-0104 (Fax)