W076/M452 replacement cards

From: Mike Cukr <cukr_at_massnet1.net>
Date: Mon Dec 1 19:09:14 2003

----- Original Message -----
From: "vrs" <vrs_at_msn.com>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk_at_classiccmp.org>
Sent: Monday, December 01, 2003 6:40 PM
Subject: Re: W076/M452 replacement cards


> > Sorry about the delay...I'm afraid its 100ma, apparently there is
> > a R/C network across the relay, I go a reading of 196 ohms
> > (close enough to 200 ohms to call it that). This may be a
> > 'fast acting' relay of higher ohmage, but the circuit might be
> > designed for a worst case of character by character control.
> >
> > I'm afraid it's back to the drawing board.....
>
> That is just weird. According to my calculations, DEC's circuit applies
> 15.7V across this relay and it's series resistor, with at most 57ma before
> the components exceed their ratings. 15V/200 ohms = 75ma, so the circuit
> can't work like that
>
> I was expecting *at least* 300 ohms for the relay and it's series
resistor.
> Did you measure at the relay, or at the cable?
>
> Assuming what you say is true, the 0.7V supply will be drug below ground,
> and the whole circuit will draw 20V/350 ohms = 57.1ma. That puts the
> components right at their operational limits, but might actually be the
way
> things work.
>
> Vince
>
I measured at the cable. I acted like there is a R/C network across the
relay,
that is the reading went up over several seconds to just under 200 ohms. It
appears that there may not be just a simple relay.

Mike
Received on Mon Dec 01 2003 - 19:09:14 GMT