[OT] measuring DC wall wart

From: J.C. Wren <jcwren_at_jcwren.com>
Date: Fri Jun 7 16:27:27 2002

        Most of the Hayes modem platforms required AC because the negative voltage
for the RS-232 was generated from it, along with the negative voltage rail
for some op-amps. In the case of a Hayes modem, it shouldn't have affected
basic off-hook and command functions, but audio would be pretty bad, DTMF
synthesis may or may not work, and RS-232 would be out of spec (but probably
workable, since most RS-232 will work at GND and +5)

        --John

-----Original Message-----
From: cctalk-admin_at_classiccmp.org [mailto:cctalk-admin_at_classiccmp.org]On
Behalf Of r. 'bear' stricklin
Sent: Friday, June 07, 2002 17:10
To: Classic Computer
Subject: Re: [OT] measuring DC wall wart


On Fri, 7 Jun 2002, Chris wrote:

> I think I am going to dig out the modem it goes to, and test the voltage
> with it hooked to that. That will at least give it real use load (the
> modem powers up just fine, it just fails to respond to all AT commands
> except for getting the firmware, and it won't attempt to go off hook or
> dial... I'm not 100% convinced the modem is really "dead" so much as it
> just doesn't want to co-operate).

Hey, you know what? I missed the beginning of this thread, but this is
exactly the sort of behavior you get from a modem which requires a 9V AC
power supply, when you run it with a 9V _DC_ supply.

ok
r.
Received on Fri Jun 07 2002 - 16:27:27 BST