4 Jun
2005
4 Jun
'05
10:35 a.m.
On Sat, 4 Jun 2005, Richard A. Cini wrote:
By the way, the power supply, so far, has tested fine.
I'm going to look
for any ripple with the scope later today. I've never done that test --
should I DC or AC couple the scope for that test?
My S-100 lore / experience is decades old now - but, ISTR that the main
supply in most early S-100 boxen was just a brute-force
transformer-bridge-filtercap arrangment that fed about 8 raw DC volts to
the cards, which were then responsible for 'taming' and regulating that
raw DC to a meek and smoothly tractable 5V.
So if you look at the (unloaded) voltage coming from the PS - it's
liable to look more like a battery charger than a computer power supply...
And for sure, 'AC' couple the scope, otherwise the DC offset will drive
the trace past where the 'vertical' control is capable of restoring it -
unless you set your 'volts per division' switch to 10 or 20 to get a trace
on screen, you won't be able to see 100 mV very easily at that resolution
(in 'DC' coupling mode, that is)
Cheers
John