9 Dec
2001
9 Dec
'01
3 p.m.
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9 Dec
9 Dec
4:55 p.m.
see below, plz.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Sunday, December 09, 2001 2:00 PM
Subject: 8" drives and PSUs.
I think you meant DOUBLE-SIDED, Tony, as the 801's are DD capable and always
have been.
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).
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.
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.
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
5:39 p.m.
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