[sebhc] H89 BOOT SUCCESS
Paul A. Pennington
paulpenn at knology.net
Thu May 17 16:45:37 CDT 2007
> The power supplies in all Zenith products prior to the Z-100 series were
> linear power supplies, while the power supplies in all PCs are switching
> power supplies.
Not true: the H/Z-89/90 had the mother of all switching power supplies
inches away from the disk drive in the form of a CRT assembly. I glossed
over that detail because I thought everybody on the list already knew that.
> There is no issue with a linear supply being "open" vs. in
> a metal box. In fact, the reason for the metal box is that switching
> supplies have lethal voltages in them, while linear power supplies do not
> (except on the primary side of the main power transformer).
My experience on that has been different. While protection is one
reason to enclose switchers, a bigger benefit, in my opinion, is less
radiated noise from the switching circuitry. You don't have to take my word
for it: bring an oscilloscope probe near an open switcher (or CRT). You'll
see some pretty wild voltages floating around.
My statement about Heath vs. PC's was based on swapping several Tandon
disk drives between a Z-100 (non-CRT model) and an original IBM PC. To me,
this pins the noise down to the switching power supply: some drives that
worked in the PC would not work in the Z-100. I observed the same thing
with Kaypro computers (with open switcher) vs. the PC.
That's my story, and I'm sticking to it :-) On what do you base your
opinion that radiated noise from switching power supplies is "not relevant"?
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