Binary Dinosaurs Computer Museum
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Research Machines 380Z
Originally touted as a kit-built 280Z this is the machine that started a lot of schoolkids, me included, on the road to 'proper' programming. At home I had a ZX81 that I was using to play amazing games like 3D Monster Maze and large blocky versions of Asteroids and this brought me into a totally different world. The original 380Z came in a blue and white case with blue keyboard and loaded BASIC from cassette as did the original one we had at school. Initially I tried converting BASIC listings from magazines but TinyBASIC didn't have a lot of the functions required so instead I ended up doing what a lot of people did and wrote a database application that stored blocks of records on tape.
Then we got a dual drive disk version with CP/M, my first introduction to it - tapes could be consigned to history! My database application suddenly became dual drive and very workable, I wish I still had a printout of it. Our machines were mono only but the platform was very expandable thanks to a 50-way interconnecting ribbon cable that linked all the options together, cards available were colour, hi-res graphics, TV modulator, RAM expansions, a Host Interface Board for connecting SASI "Winchester" disks and a high speed serial network interface called CHAIN.
This machine came from a lad in Dartford who'd stored it at work for 18 months, previous to that it had obviously been in a damp environment and thanks to a perspex cover that wasn't fastened things had obviously been a bit wet in there. I wasn't too au fait with PSU testing back in 2011 so restoration was shelved.
2011 Pictures
2017 Update
Fast forward 6 years and both my stock of test equipment and knowledge have expanded substantially. :) Having recently repaired my Link 480Z I thought it was time to tackle the machine again. Stripping it down to remove the PSU lump I discovered the wet HAD had an effect in that most of the RAM chips on the colour VDU board had rotted. Fortunately they're MK4116 DRAMs so they were easily replaced.
One of the glass fuses in the PSU was popped so it was time to tackle the dismantling job and testing the various output components - getting this PSU out of the case is no mean feat. However, I quickly found a dead short so decided to use one of my triple-output T60B PSUs for board testing. A base machine only needs the CPU and video board so I removed everything else and looked at power input. The power connector to the CPU board is a 10-way ribbon cable so armed with the PSU schematic and a DMM I traced out the connector and made up 2 new harnesses (hi-res video board needs one too), checked and triple checked everything and POP! Magic Smoke.
All the power capacitors are tantalums which can fail dead short and this is what had happened here. Normally the tant will explode but unfortunately a 12V rail trace took the brunt of the damage and failed. I replaced the dead one and retested all the others, repaired the damaged trace and this time not only did I get a steady 12V but I also got a COS prompt, first time I'd seen that since school :D
Keyboard was fine so I tested the tantalums on the 32K RAM board and floppy controller and installed them. Cleaned up the floppy drives and just for safety used another T60B PSU for power and not only did I get a COS prompt but after a few goes with a head cleaning disk it booted a CP/M disk and reported 56K RAM. Happy days. Next up is repairing the damaged colour video board and testing the PAL output board.
Update, after completely dismantling the PSU I discovered it wasn't the 12V filter capacitor that had a short, it was the (you guessed it) tantalum cap feeding the main 12V regulator. After replacing ALL the tantalums on the board and retesting the massive filter caps I hooked up an old hard drive for load and.... power up!
After putting it all back together with no pocket screws left over it was an absolute joy to see it run under its own power since the 80s.
2017 Pictures

All images and text © Adrian Graham 1999-2018 unless otherwise noted using words. Also on