Re: [N8VEM-S100:1353] New/Old Project

[Douglas Goodall <douglas...@mac.com>]

Eric,

Our group consists of lots of old-timers and youth as well.

Apparently all of us like to fiddle with hardware, and there is quite a lot of fun going on.

The major interests within the group are focused on a range of hardware, as simple as a single
board computer (See the Zeta), and more sophisticated buss oriented systems, both S-100 and ECB.

Andrew supplies bare circuit boards for us, mini boards, SBC's, and a highly integrated machine we
started calling the N8 (originally named "Home Computer").

John sells S-100 bare boards, CPU cards, memory boards, ...

There are two main Google mail groups, one for Andrew's focus (n8...@googlegroups.com) and one
for John's (n8vem...@googlegroups.com). There is another one recently formed for the scsi to ide
project, aka S2I.

Information about the boards, schematics, board layouts, etc are found on the wiki (n8vem-sbc.pbworks.com).

Building these boards is a learning experience, and we gain knowledge about sourcing parts, building  up
boards and then debug them. The community members are very happy to help each other get things working
the google groups are a constant stream of questions and answers about aspects of the hardware and
software.

There are a number of different BIOSs written by community members, some of which are more specific and
some of which are more productized and full featured. If you want to find out more about the boards, look 
under board information on the wiki. There is a software information section as well.

Welcome to our community, and don't be shy to communicate with us via the lists or privately.

Regards,

Douglas Goodall

On Feb 2, 2013, at 1:23 AM, Eric O <ewok...@gmail.com> wrote:

> Andrew Lynch suggested I join this group and seek assistance with my "project". 
> 
> Background:
> Back in 1975 I was a 20 year-old electrical engineering college student and electronics hobbyist and saw the famous Popular Electronics article on the Altair 8800 computer.  I ordered it, assembled it and it worked great as soon as I powered it on for the first time.  Over the next year or three I enhanced it with some additional memory, a homebrew parallel and serial interface and the Processor Technology video card.  I wrote hand-assembled machine code to "boot load" my own little monitor via a modem to the mainframe computer on campus.  This involved an automated log-in to my account, starting the listing of a hex file and then capturing and loading that hex file into the Altair RAM.  Of course I had to switch a couple hundred bytes of machine code into the Altair whenever I needed to "reboot".  I also wrote a terminal emulation program so I could then use it as a terminal to that same mainframe.  Great fun and done on a shoe string because I was a very poor college student.
> 
> Disaster literally struck out of the sky one day around 1979 when a very powerful thunderstorm hit and a lightning bolt literally blew the top off the power pole that fed the off-campus house I shared with three other students. I should have unplugged the Altair when the thunderstorm arrived, but I didn't want to have to take 15 minutes to reboot it.  Stupid!  Anyway the power surge killed the machine.  It would still light up but it wouldn't do anything approaching normal operation.  I did replace a number of the chips in the weeks that followed, but I couldn't afford to do a proper job of it.
> 
> Well, graduation came, then a job, then an IBM 5150, and then other computers over the decades and now the Altair has been stored in a box for almost 35 years.  I always meant to fix it someday but never got around to it.  But now that I'm semi-retired from a career in computers I'm finally getting around to it.  So a couple months ago I finally got it out of that box and started doing a bit of research and I'm so happy to see all the love that people have for these old machines.
> 
> One of the first things I learned was not to trust the original power supply.  So I went out and got a couple switching power supplies from MeanWell, mounted them up in the chassis, and leaving the old supply physically in place, removed it electrically and replaced it with the new supply.
> 
> I popped out all the boards, and turned it on.  I'm getting all the proper voltages in all the proper places,  including regulated +5.13 on the display board.  With the CPU in I get the proper regulated voltages on the CPU card: (-5.25 on Pin 11, +11.69 on pin 28, +5.00 out of the regulator).
> 
> I've started working on the front panel and I've already identified two inverters with the same logic state on each side of the gate, on two different chips.  So I know I need to replace those.
> 
> Any and all suggestions welcome.
> 
> (I've seen the very good article at http://s100computers.com/My%20System%20Pages/Debugging/Debugging%20for%20beginners.htm)
> 
> Eric O
> 
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---
Douglas Goodall, http://goodall.com

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