30 Jul
2006
30 Jul
'06
12:45 a.m.
If I'm reading things right, the Imsai 8080 directly switches AC power
through the front panel power switch. Can someone suggest a relay circuit
to remove the need to run so much power through the front panel?
--
David Griffith
dgriffi at cs.csubak.edu
A: Because it fouls the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?
30 Jul
30 Jul
1:01 a.m.
David Griffith wrote:
If I'm reading things right, the Imsai 8080
directly switches AC power
through the front panel power switch. Can someone suggest a relay circuit
to remove the need to run so much power through the front panel?
Is there a reason *why* you don't want to switch it the
same (original?) way?
Do you have a source of "standby" power available to drive
a relay coil?
How much do you really *want* to do this?
1:36 a.m.
On 7/30/2006 at 1:01 AM Don Y wrote:
David Griffith wrote:
The Altair MITS 8800 also has an AC switch set up this way, which made for
"interesting" times when probing. A compromise might be just to cover the
traces with something that will avoid any bare conductors "zinging" you,
such as PCB resist. Althernatively, one could simply bypass the switch on
the front panel and switch the mains power externally--that's a change that
can be easily reversed.
Just some food for thought.
Cheers,
Chuck
If I'm reading things right, the Imsai 8080
directly switches AC power
through the front panel power switch. Can someone suggest a relay
circuit
to remove the need to run so much power through
the front panel?
Is there a reason *why* you don't want to switch it the
same (original?) way? 
9:32 a.m.
New subject: IMSAI CPU (MPU) card?
Heya all, I'm still looking for anyone that has an extra or not needed cpu
card for the IMSAI 8080. I rescued one with the processor card removed,
and I'd like to get this up and running some time in the future.
Thanks!
Marty
2:40 p.m.
New subject: IMSAI CPU (MPU) card?
On Sun, 30 Jul 2006, Martin Scott Goldberg wrote:
Heya all, I'm still looking for anyone that has an
extra or not needed cpu
card for the IMSAI 8080. I rescued one with the processor card removed,
and I'd like to get this up and running some time in the future.
I have a couple in the storage unit. Next time I go there (tomorrow?)
I'll dig one out. Please email me privately.
--
David Griffith
dgriffi at cs.csubak.edu
A: Because it fouls the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?
4:57 a.m.
I actually did this modification on my IMSAI a few months back. I found an
old 5v wall wart and a small 5v relay. I cracked open the wall wart so I
could direct-wire things and then I potted it with the cover off and with
just the wires coming out (I bought potting compound at Mouser). I wired the
primary to the power switch/fuse on the back panel (which may or may not
have been original) and put the front panel switch in series with the
secondary and the relay coil. The relay contacts "replaced" the switch that
was on the back panel, which switched everything else.
My IMSAI did not have a fuse holder on the power supply PCB (there was one
on the back panel), so I removed the jumper that was in that spot and
replaced it with a Molex connector that matched the one I put in the relay
contact loop. Therefore, I could un-do the mod with little effort and just
put a jumper connector on the Molex if I had to.
The switch on the back panel is now a master power switch while the front
panel switch only switches low voltage. It actually works pretty well and
was made with a bunch of junk box parts.
Rich
Rich Cini
Collector of classic computers
Lead engineer, Altair32 Emulator
Web site: http://highgate.comm.sfu.ca/~rcini/classiccmp/
Web site: http://www.altair32.com/
/***************************************************/
-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of Don Y
Sent: Sunday, July 30, 2006 4:02 AM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: imsai 8080 power switch
David Griffith wrote:
If I'm reading things right, the Imsai 8080
directly switches AC power
through the front panel power switch. Can someone suggest a relay circuit
to remove the need to run so much power through the front panel?
Is there a reason *why* you don't want to switch it the
same (original?) way?
Do you have a source of "standby" power available to drive
a relay coil?
How much do you really *want* to do this?
6:14 a.m.
Don Y <dgy at dakotacom.net> wrote:
David Griffith wrote:
It is a good idea because everybody who ever had a IMSAI has reached
inside to tinker with something nearby on the front panel when
"YOWZAA, That's Live" becomes the only thought in the head!
If I'm reading things right, the Imsai 8080
directly switches AC power
through the front panel power switch. Can someone suggest a relay circuit
to remove the need to run so much power through the front panel?
Is there a reason *why* you don't want to switch it the
same (original?) way? How much do you really *want* to do this?
One very common (and even mentioned in the IMSAI manual) modification
is to not use this switch for 120VAC, but to use it as a write-protect
toggle for a bank of RAM. With the original low-density (1K, 2K, 3K,
4K) memory boards this is reasonable, and some higher density boards
even supported this kind of option. In this case an external
switch or a switch on the back panel (one would hope with some kind of
insulation on exposed terminals!) is used for AC power.
The concept of an "original virgin" IMSAI 8080A is quite odd anyway. These
were heavy-duty hacking machines owned by the heavy duty micro hackers,
and if someone had a good idea that required a hole or two in the back
or some rewiring on the front they didn't let anyone dictate whether
they should do it or not. For
a while in the 90's I "restored" hacked-up IMSAI 8080A's back
to "original" condition but in retrospect the hacked-up versions
are MORE authentic of how they were used.
Tim.
8:32 a.m.
From: shoppa_classiccmp at trailing-edge.com (Tim
Shoppa)
---snip---
a while in the 90's I "restored"
hacked-up IMSAI 8080A's back
to "original" condition but in retrospect the hacked-up versions
are MORE authentic of how they were used.
Tim.
I restored mine but that was mainly because the switch they'd
used was a too small for the load.
The switch came in handy as a format/mormal switch for my
floppy controller :)
There are many places in an IMSAI that I can get zapped. I
don't consider that particular location on the front panel even
easy to get to.
Dwight
Dwight
2:32 a.m.
David Griffith wrote:
If I'm reading things right, the Imsai 8080
directly switches AC power
through the front panel power switch. Can someone suggest a relay circuit
to remove the need to run so much power through the front panel?
How much is "so much" ? If it's the sort of DT switch I normally see on old
equipment then it'll be rated for at least 5A at input voltage, possibly 10A.
I doubt an Imsai would be drawing much more than half the rated value at most,
to be honest; better candidates for things to be worrying about are probably
things like kettles, driers and washing machines where they're still
power-hungry but can run in a far more disagreeable environment (e.g. you're
not likely to be running an Imsai if it's wet :-)
cheers
Jules
10:16 a.m.
Hi,
If you don't want to just use external switched outlet or "AC power
strip", consider using a Crydom SSR (Solid State Relay), These are
blocks which switch electronically at zero crossing; require various low
DC voltages at input to turn on; some take logic levels IIRC. You can
use power switch on panel to control a small supply which generates the
SSR control voltage.
Should be possible to use a decent wall wart for this; maybe placed back
near the IMSAI xfmr. It's been 26 years since I last saw mine. YDMV.
Steve
David Griffith wrote:
If I'm reading things right, the Imsai 8080
directly switches AC power
through the front panel power switch. Can someone suggest a relay circuit
to remove the need to run so much power through the front panel?
31 Jul
31 Jul
7:54 a.m.
From: Steve Stutman <Steve at oceanrobots.net>
Hi,
If you don't want to just use external switched outlet or "AC power strip",
consider using a Crydom SSR (Solid State Relay), These are blocks which
switch electronically at zero crossing; require various low DC voltages at
input to turn on; some take logic levels IIRC. You can use power switch on
panel to control a small supply which generates the SSR control voltage.
Should be possible to use a decent wall wart for this; maybe placed back
near the IMSAI xfmr. It's been 26 years since I last saw mine. YDMV.
Steve
Hi
One thing you should know about zero crossing. You don't want to use
a zero cross relay on a highly inductuve load( the IMSAI might qualify
as highly inductive because of the large core used ). You want a peak
switching. Zero cross is the worst place to turn on an inductive load
and results in the highest current surge. This may even saturate the
core and cause a peak several times the normal running current.
Dwight
6719
days inactive
6720
days old
10 comments
9 participants
participants (9)
-
cclist＠sydex.com -
dgriffi＠cs.csubak.edu -
dgy＠DakotaCom.Net -
dkelvey＠hotmail.com -
julesrichardsonuk＠yahoo.co.uk -
rcini＠optonline.net -
shoppa_classiccmp＠trailing-edge.com -
Steve＠OceanRobots.net -
wgungfu＠csd.uwm.edu