I once found a handy gadget for seeking adjacent line shorts on the S-100.
It's essentially a board with the edge connector and little else, except
that the pins on one side are connected. Since the lines tend to be laid
out alternating from one side to the other, your audible squeaker will allow
you to test one side at a time with the "other" probe tide to the opposite
side. Finding shorts is really quick and easy with this. It's easy make,
though several vendors sold them at one time. Fortunately, it's built
without the part of the board which would prevent you from reversing it, so
you can do just that. An unaltered board with the connections on one side
shorted wouldn't quite work due to the mechanical offset which prevents you
from reversing a board.
Dick
-----Original Message-----
From: James Willing <jimw_at_agora.rdrop.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Thursday, June 24, 1999 2:20 PM
Subject: Re: Just scored an IMSAI
>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
>Computer Garage Fax - (503) 646-0174
>
>>>> Coming soon to www.computergarage.org - the CBBS/NW on-line archives
>
>>>> Coming to VCF III (2-3 October 1999) - CBBS/NW live!
>
Received on Thu Jun 24 1999 - 15:20:41 BST