24 Jun
1999
24 Jun
'99
9:55 a.m.
Well, much to my amazement, at lunch today, I got
an IMSAI 8080. In beautiful condition, a few small
scratches, almost no dust. Hasn't been up in years.
I know we've done this before on this list, but...
Where should I start?
I figure:
1) pull all cards.
2) attach dummy load and check PS voltage
and amperage.
(What is an appropriate dummy load?)
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.
4) install CPU and see if it "lights up"?
Thanks,
Bill Sudbrink
24 Jun
24 Jun
11:15 a.m.
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(a)computergarage.org
The Computer Garage - http://www.computergarage.org
Computer Garage Fax - (503) 646-0174
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CBBS/NW on-line archives
>> Coming to VCF III (2-3 October 1999) - CBBS/NW
live!
11:18 a.m.
On Thu, 24 Jun 1999, Bill Sudbrink wrote:
Well, much to my amazement, at lunch today, I got
an IMSAI 8080. In beautiful condition, a few small
scratches, almost no dust. Hasn't been up in years.
I know we've done this before on this list, but...
Where should I start?
I figure:
1) pull all cards.
2) attach dummy load and check PS voltage
and amperage.
(What is an appropriate dummy load?)
I might be a good idea not to do this step at this time... (see
below): the IMSAI power supply is a brute-force, very simple design
that puts out loads of current at slightly higher than needed
voltages, and then relies on regulators on the individual cards to
do the final power steps. I emphasize Lots of Amps available... it
is not a modern supply (like is used in most small computers today)
and does not require a dummy load to function. It is a Neanderthal
power supply.
The most hazardous part of brining up an old brute-force power
supply like the IMSAI (and many other S-100 machines) is that the
large electrolytic capacitors have dried out or become 'unformed'
with age, thus presenting a dead short to the rectifiers thay are
hooked to. Thus you can get fireworks if you just slam the power to
it. If you can get the use of a Variac or similar variable
transformer of about 5 amps capacity, then place it in the mains
circuit and use it to s-l-o-w-l-y bring up the voltage on the power
cord, watching for signs of overload... bad humming, things getting
warm, etc. Do this over a period of maybe an hour or so... from )
vols, turn it up a few percent, leave it for a while, then repeat
until you have full mains on the power supply and you can measure
around 8 volts DC on the main power terminals. It is recommended
that you get copies of the docs for this before going much farther.
Also there are many folk on The LIst who have these machines (as
do I) who can help you with bringing it up after it's long sleep.
There is a way to do this with a bank of 100W incandescent lamps,
but that requires a lot of wiring stuff.
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.
If power is good, I'd put in the CPU and see if the panel can
examine and load and address data...
4) install CPU and see if it "lights up"?
Then the rest of it, too... did you get any disk drives? Other
peripherals? Documentation? Software??
Nosy minds want to know...
Cheers
John
11:52 a.m.
Then the rest of it, too... did you get any disk
drives? Other
peripherals? Documentation? Software??
Nosy minds want to know...
Here's what I got:
Case w/front panel and PS.
All cards were collected from another location
(were not in the case):
IMSAI MPU-A REV-4
IMSAI MIO REV 2
IMSAI VIO REV 2.1 AR 1.1
Cromemco 4FDC (2 each, floppy controllers)
Cromemco 8K BYTESAVER(tm) (eprom programmer?)
VAMP inc. "EXTERMINATOR" VTE 100a (bus elevator card)
S.D.Sales EXPANDORAM(tm) (looks like 64K DRAM)
INDUSTRIAL MICRO SYSTEMS 8K MEMORY BD. (8K of 2102 SRAM)
Documentation for some of the above (have not reviewed in
detail yet).
Shugart 801 no case or PS
Bill
2:03 p.m.
John Lawson <jpl15(a)netcom.com> wrote:
If you can get the use of a Variac or similar
variable
transformer of about 5 amps capacity, then place it in the mains
circuit and use it to s-l-o-w-l-y bring up the voltage on the power
cord, watching for signs of overload...
Hi
As a safety issue, point the can in a safe direction with
something like a pillow to stop its flight. One should also wear
enclosed safety glasses. Old tantalums may also explode and
create electrical fires. Be ready to remove electrical power
for at least 5 minutes after initially powering on.
Again, safety glasses are recommended. Fast pieces of hot
epoxy can do damage to your eyes. Try to remember to not
be in the launch zone to the larger electrolitic cans.
They can move with damaging force. I've seen these go
off 3 times. Also, do this in a location that won't be too
damaged by little tiny bits of borate soaked paper
( the old cereal slogan comes to mind "shot from guns" ).
Dwight
12:09 p.m.
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