April 1999
Lucky day! I found myself staring at an eBay auction and
a photo of a Mark 8 circuit board. I could hardly believe my eyes. The
seller had advertised (one board at a time!) a "circuit board for
parts". The boards were listed under "Toys" or some
similarly ridiculous category. The only reason I found them was a search
hit on a different item the seller had listed. I checked the sellers
other auctions, and ta-da! There they were. Conscience got the best of
me; I emailed the seller to inform them of what they had. The seller had
an "oh, well" attitude about it and the auctions proceeded.
Although there were other bidders, I had no intention of being
outbid, and now the Mark-8 is mine!! All mine!!! Aah-ha, ha, ha, ha, ha,
ha, ha, ha, he, ha, he, he, hah, hum, ho, hee, he-heeeee.............what?
After winning all the auctions, the seller contacted me
and asked if I wanted the "whole box of junk", of course I
said yes!
The Boards
The Mark-8 consists of six boards, shown below. (Click
on the thumbnails for a larger view.) The processor board is a new scan
compared to the others. My original scan was without the C8008 chip, as
I was testing parts of the board, and forgot to put the chip back for
the photo. All the other scans were done soon after I received the
boards.
I began restoration by learning how every circuit was
intended to function, and then I tested every circuit in isolation on
every board, one board at a time. This I did by building a signal source
and signal display interface for each board, and then by simulating
every signal the board might ever expect to see. Then I traced out each
signal and verified the output signals. Every gate, flip-flop, and
counter was thoroughly tested on every board. I tested the first hundred
or so memory locations and a few from every 256 byte block in the bank.
The remainder of memory locations were tested under program control when
the machine was fully operational.
Spring 2000
Found a nice pretty C8008 to replace the
all-scratched-up one that came with the boards. Finished analyzing and
learning the circuitry, finished testing all of the circuits on all of
the boards. To my surprise, not a single malfunction was detected in all
the computer. I do have a few bad LED's on the Register Display board,
and a few broken pins in the Molex connectors.
I have this great idea of putting the boards into a new
cabinet to match the one on the cover of RE. Cool idea, huh? I am nearly
finished reassembling the boards into a "replica"
"original" wood card cage, and I have a full set of vintage
toggles identical to Jon Titus' original, except that mine are blue.
September 2000
A full blown Mark 8 Minicomputer replica just sold on
eBay. Steve, the builder, and I had exchanged emails earlier in the
year, and I knew he was planning to build one, but wow! There it is!
Now that Steve has built a couple replicas, I have
decided to restore my Mark 8 as close as possible to the original
condition, using all the parts I received from the previous owner,
rather than risk having it thought of as just another replica.
Although I have fully restored the transistorized power
supply, I chose not to use it since it has poor regulation compared to
chip regulators, and no over-voltage or over-current protection. I have
installed a chip based regulator in the main housing, side-by-side with
the transistor based one. The original transistor based regulator is
disconnected.
Spring 2001
My Mark 8 is fully restored. With the processor chip in
place, hours went by before I had the nerve to flip on the power switch! I
looked over the connections one last time, took a deep breath, and,
>CLICK!!< Lights on, no smoke! It worked almost
flawlessly! (I missed a bad connector finger on one of the boards that
caused one of the lamps to flicker.)
I loaded a short program and single stepped through it a
few times:
00 000 104
Jump
00 001 000
00 002 000
This single instruction program just jumps to itself
continuously. By the end of the next day, I had it connected to my
ASR-33 Teletype, and running a save and restore program from paper tape.
Ah! So what is the extra chip doing on the Input
Multiplex card? It maps data from the front panel switches to an input
port. It allows data entry from the front panel switches under program
control. The original Mark 8 had no provision for reading the front
panel switches while running a program!
July 2002
I have put together a TCP/IP interface and connected the
Mark 8 to my home network. I run it at 300 baud, and connect to it
through Telnet.
September 2002
My latest project is building a hardware stack so I can
save all the registers and condition codes when I run a subroutine. The
hardware stack will plug into an I/O port with no modifications to the
computer. The I/O instructions will perform the stack Push and Pop. I'm
also looking for a copy of SCELBAL so I can run BASIC programs on my
Mark 8 from over the internet!
With a little luck, one day you may be able to log into
my Mark 8 from this web site and run your own programs!
Late 2002-early 2003
Found a photocopy of SCELBAL, as well as a source
listing and a couple of emulators running SCELBAL. In my spare time...
uh, hummm.... I will be adding some memory to my Mark 8 so I will have
enough to run it! Weeks after finding a photocopy, I have found an
original copy.
October 2003
I packed up my Mark 8 computer and a few other items,
and went to the VCF 6.0 in Mountain View, California. We cleaned up in
the awards! Go see the pics!
