IMSAI Score update/Spare BYTEs/Got an Altair too

[John Lawson]

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