Original Dick Smith System 80 Mark 1 lives again!
The Dick Smith System 80 was my first computer hence it's a nostalgic favourite. During its production run, tweaks were made to the basic design to aid program loading, improve the user experience and make it more compatible with the TRS-80 Model 1. I have examples of later variants but until now did not own a "first release". A boxed example of this DS System 80 original came to me in a donated haul which also contained a TRS-80 Model 1 (Level 1 BASIC) which in itself is another "original".
You can tell this System 80 is the first off the line due to the absence of a level meter and volume control above the tape deck. Also, there is no CLEAR or TAB key, the latter providing the forward arrow for TRS-80 Model 1 programs. The machine was often sold with a Dick Smith monitor (actually a modified TV) which was a common accessory for those that didn't want to use the family television. Luckily, I got one of these monitors with the computer also. To round it off, the manuals were also in the package.
Figure 1. Dick Smith System 80 Mk 1 (first variant) and accompanying goodies
Switching on however, revealed a problem. Only the bottom 1/2 of the screen was visible and of that, all the spaces were showing up as @ symbols! They say experience counts for a lot when fixing old computers and indeed experience came in handy here. I'd seen similar symptoms before and deduced this was a video RAM issue.
Figure 2. Screwy video. @ instead of space
The video RAM in the System 80 is conveniently socketed and I had spares. I started to swap the chips out and in no time at all had a working machine. The defective IC was the second from the bottom.
Figure 3. Red arrow shows the faulty video RAM
There is one interesting (reversible) after-market addition to this machine. Note the green-stickered 2716 EPROM on the lower left underneath the three ROMs. Just what it does I'm not sure but it's likely to add a few utilities. I'll investigate its function as time allows.
So, the machine was now up and running. But would that tape deck still work? Even with a non-stretched belt to turn the cogs, the lack of a gain control made tape loading in early System 80s somewhat of a lottery. With low expectations I tried out my cassette version of Dick Smith Space Invader. Waddaya know, the program loaded first time! Amazing!
Figure 4. Space Invaders anyone? The fully-working DS System 80 Mk1 locked, loaded and ready to go?
So everything appears AOK with this unit. Another one to add to the stash. I've now got examples of three variants of the cassette-enabled Dick Smith System 80. I'd love to get the one with the numeric keypad though!
13 March, 2015