On Thu, 24 Jun 1999, Bill Sudbrink wrote:
> Well, much to my amazement, at lunch today, I got
> an IMSAI 8080...
Congradulations!
> Where should I start?
>
> I figure:
>
> 1) pull all cards.
Yep... Then I frequently do a quick 'shorts' check on the S-100 backplane
before proceeding. Take a ohmmeter on a low resistance setting and step
across the opposing pins with the leads. Start on pin 3, pin 53, then pin
4, pin 53, then pin 4, pin 54, and onward across the backplane. This will
quickly catch any adjacent line shorts. You may also reverse the stepping
sequence in case the backplane is an oddball and the lines are interleaved
differently.
Skip pins 1,2,51,52,50, and 100, since these are the power supply pins and
will give readings back thru the power supply components.
(note: pins 1/51 = +8VDC, pin 2 = +12VDC, pin 52 = -12VDC pins 50/100 =
GND)
> 2) attach dummy load and check PS voltage
> and amperage.
> (What is an appropriate dummy load?)
Well... (and I'll probably catch some heat for this) since the IMSAI
supply is an unregulated linear supply (regulation is done on each
individual S-100 card), a 'dummy load' is not really necessary for a basic
check. (switching supplies need a load or they get unhappy)
There are only three voltages on the bus, +8VDC, +12VDC, and -12VDC, which
in reality are usually closer to +10~12VDC, +16~18VDC, and -14~18VDC.
With the cards out, you can check these with a voltmeter. Now, where you
may want to load things up a bit is for a 'ripple' test. (looking for
bad/leaky capacitors &/or bad rectifier stacks. Although a bad recifier
will often cause the line fuse to blow)
Depending on the amperage rating of the supply, (the IMSAI is a honker!) I
have a bank of automobile lamps (headlights for high amp, taillights for
lower). I gang these together for the appropriate voltage/amperage
ratings and 'light it up'! (pun intended) Then you can look for odd sags
in the voltage, and if you have a 'scope look for ripple on the suppliy
lines.
> 3) check front panel mechanically. Use an
> OHMmeter to be sure that all switches are
> opening and closing correctly? I seem to
> remember that some people said that front
> panel disassembly/assembly is tricky.
Not THAT complicated, but there are LOTS of screws, spacers, etc...
Usually I just do a 'click' check on the switches, (toggle them and
listen. Bad ones will often make either a muffled sound or no sound at
all), and then do a function test once the panel and CPU boards are
plugged in.
> 4) install CPU and see if it "lights up"?
After a final 'visual' check for bad/damaged/improperly installed
components, etc...
Ever onward! YMMV!!
Regards;
-jim
---
jimw_at_computergarage.org
The Computer Garage - http://www.computergarage.org
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Received on Thu Jun 24 1999 - 15:15:22 BST