27 Jan
2001
27 Jan
'01
9:16 a.m.
Tony Duell wrote:
[snip]
What I have never managed to find out (and if anyone
here knows, please
let us all know) is (a) what power line this resistor loads (it has to be
either +5V or +12V as it connects to a drive power connector) and (b)
what is the resistance (and wattage) of this resistor.
Caution: What follows is from memory which is increasingly subject to
bit rot.
My recollection was that it loaded the 12V line, not the 5V line. I
don't recall the value nor the rated wattage, but it was packaged
in the finned metal package (as opposed to ceramic) that I generally
associate with things dissipating above 5W -- and it was sporting
heat sink compound between it and the cage, suggesting that there
was at least an attempt being made to dump heat into the rest of the
chassis.
I'm not sure how essential it is either. Certainly
most PC/AT PSUs don't
like running with no load (they trip, they don't fail permanently), but
in my experience only the 5V line needs to be loaded, and the motherboard
will do that. Certainly I've run PC/AT machines without a hard disk and
without this load resistor.
As have I (that machine, in fact). My assumption was that it simply represented
conservative design on the part of IBM to avoid the 12V supply becoming
unloaded when the floppy wasn't running.
-ck
--
Chris Kennedy
chris(a)mainecoon.com
http://www.mainecoon.com
PGP fingerprint: 4E99 10B6 7253 B048 6685 6CBC 55E1 20A3 108D AB97