This machine, and a couple others are really the starting point and inspiration for this site. I figure, in that case, I ought to give them a mention.
Starting with this, one of three machines left over that were in good enough shape to recover from years of damp storage. Wikipedia has a page about it (TRS-80 Model III).
I say that about this site because I came by this via a work colleague. His brother in law was clearing a house he had for sale and these were in storage inside, no climate control (ever read the operational/storage parameters for electronics? 120F/80% rH non-condensing – Storage) in the wonderful swampland of south-east Louisiana. He asked if anyone was known who’d be interested in taking them, rather than it all going straight in the dumpster. My name was mentioned. The rest, as they say, is history.
Anyhow, this is the beast in question, after a rather hasty scrub-up to remove about a decade of grime from storage and then operational gunge.
48kb of RAM.
2 MHz of Zilog’s finest 8-bit processing power.
Incompatible text display.
In the true spirit of things, and considering I was at work, the first thing that happened was it got pulled apart.
This one is a fairly advanced model, having a pair of floppy drives in. That means there are two Astec power supplies inside. One runs the screen (12V, it’s basically a portable TV without the tuner), the serial card and motherboard, the other runs the floppy drives and controller card.
I’ve worked with those Astec power supplies before. They were used widely in Acorn machines, notably the BBC Microcomputer. They have a tendency to go bang when powered up, and were notorious even when new.
Therefore, in went a slightly modified Dell desktop power supply, rated at about double both the Astecs put together. Dismantled the brightness and contrast pots because they had seized solid, and presto:
You can see the PSU there on the left. I ended up mounting it so the fan draws in cool air from underneath the floppy drives and vents out through the grille in the top. As it forms a chimney, the fan never runs at anything other than idle and is nearly silent due to the convective nature of the box.
Works a charm there, booted up into BASIC.
It migrated around for a while, at home being poked and prodded:
In so doing I sat down and went through the entire motherboard, chip by chip to find out how it worked.
It’s from an era when you can tell there were one, maybe two people involved in the overall architecture, and you can get inside their heads a little when you look at the design:
Got it running properly, with the obligatory “Hello, World!”:
…and as the PSU is no longer switched by the main power switch on and off, the soft-on is controlled instead. Hooked up an LED into the reset button (top right of keyboard) to show power’s applied, using the clock keep-alive rail of the PSU:
Decided to run it flat-out as a test…
Gave BASIC some floating-point recursive calculation to do. Calculate pi to as many places as possible. It nearly got there.
Buttoned it all up and powered up the other bonus haul for it- the daisy-wheel printer that you could purchase for $1995. Gave it a thorough clean out and oil up, at the same time. It has the optional fanfold paper tractor on the back also.
It is noisy and slow, and with a change of cable will even talk to an IBM-PC, despite adding extra line-feeds in where they need not be. The print quality isn’t bad either, considering it’s just a glorified typewriter.
As it turns out, the controller chip on the floppy board has gone bad. It no longer outputs the signal to hunt the heads one track over- applying 5V to the pin causes the drive to hunt, so new chip needs to be obtained. Unfortunately, Western Digital’s popular FD1793 chip now commands a high price on most popular bidding sites and I honestly don’t have the patience to be ripped off for one ($45 at current market prices).
Typically also the ribbon cables fell to pieces so several hours rebuilding them meant that I was no further forward with the floppy drives than I was to begin with. However, the optional add-in RS-232 serial port card is fully functional.
With a little bit of BASIC programming, 300 baud serial communication is possible. Here it is, attached to my terminal server, displaying the output from an apt-get upgrade action on Ubuntu.
That’s about as far as I’ve gotten with the thing so far but there is light on the horizon for this one. I do plan on getting another controller chip for the floppy drives. Those 5.25″ ones are going, to be replaced by 3.5″ ones and possibly a hard-disk emulator board that runs off Compact Flash.
Fun piece of equipment. I can see why it was America’s best selling computer of the early eighties.