see below, plz.
Dick
----- Original Message -----
From: "Tony Duell" <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Sunday, December 09, 2001 2:00 PM
Subject: 8" drives and PSUs.
>
> > has two QumeTrak drives (242, I think -- full height 8"), one of the
> > no-names has two Shugart 801 drives (single-sided only, I think), and the
>
> Yes, the 801s are single-sided only. 851s are the double-density
> equivalents, almost.
>
I think you meant DOUBLE-SIDED, Tony, as the 801's are DD capable and always
have been.
>
> > other no-name also has two QumeTrak drives. Unfortunately, the power supply
> > in the no-name QumeTrak drive box literally had an LM723CN explode, breaking
> > the chip in half, melting the socket, and fusing two pins to the socket.
>
> Is this an SMPSU? The 723 could be used to make most of the SMPSU control
> circuitry (oscillator/chopper driver), but if the chopper shorts and/or
> the current sense resistor in series with the chopper openes, then the
> result is generally an exploding 723. So if it's an SMPSU, you want to
> check all the primary side components, as usual.
>
The most-common linear supply used back in the 8"-drive days was the Power-One
CP206, of which there were many copies, which used a 3 723's to control 3 pass
transistors to regulate +5, +24, and -5/-12 (depending on jumpering).
>
> If it's a linear PSU, then I guess an open-circuit in the pass transistor
> (b-c junction) could result in all the load current flowing via the 723
> or something nasty. That would probably make the chip explode as well,
> although I've never actually had this fault. Again, check surrounding
> components, particularly power transistors.
>
> -tony
>
>
Received on Sun Dec 09 2001 - 16:55:49 GMT