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Old 4th Jan 2023, 1:04 am   #1
Mark1960
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Default Microtan 65 Restoration

I thought maybe if I start a thread on my old Microtan it might get me to make a start on getting it running again.

Original build started in about 82/83 with a bare board and tanbug purchased via an advert in one of the monthly magazines of the time. A short time later I bought another processor card and a tanex. I got an old scrap verorack from work, added a self designed memory card and an ETI RTC card. I never had a proper backplane, just a lash up on veroboard for the cpu and tanex, then wired up to a cut off length of backplane for expansion cards.

I think the main boards have survived quite well considering they have spent over 40 years in less than ideal conditions. About 10 of those years in a damp garage, the rest in a loft. I guess the biggest surprise is that the battery on the RTC card hasn’t eaten the rest of the boards, probably because I sprayed the memory board with conformal coating.
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Old 4th Jan 2023, 1:22 am   #2
Mark1960
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Default Re: Microtan 65 Restoration

The original cpu board is not in such good condition as it was laid on top of the rack for many years. Its covered in greasy dust, mostly rust cleaned off cars with wire brushes over the years. I had stacked 2114s to expand the memory before I got the tanex. Most of the components were robbed to solder directly on the second board as they were known working.
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Old 4th Jan 2023, 2:42 am   #3
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Default Re: Microtan 65 Restoration

The rack itself just needs cleaning but the backplane was always a mess and really needs replacing with a pcb backplane.

I still have the clear acetate and black tape pcb layout that I made nearly 40 years ago and never got round to etching the pcb.

The rack is an old vero rack, it originally had a hinged front panel but that had been cut out for its original use, so it was discarded a long time ago.
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Old 5th Jan 2023, 8:37 pm   #4
SiriusHardware
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Default Re: Microtan 65 Restoration

If you remove the modulator from the original CPU and anything else in a socket you might be able to wash it in a sink full of detergent - the key is having something to bake it dry in immediately afterwards. I used to work for a company which specialised in the repair and refurbishment of PCBs and that is exactly what we did with them once we had repaired them. We washed then in a strong industrial detergent solution and had a temperature controlled oven for the specific purpose of drying the boards bone-dry after they had been washed.

Certain components, like relays with clear snap-on covers and preset resistors, had to be removed before this treatment - in this case you wouldn't want to fill the modulator with water, even with the lid off.
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Old 5th Jan 2023, 9:50 pm   #5
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Default Re: Microtan 65 Restoration

Thanks Sirius, I was trying to decide if I should wash that one. I’ll probably keep it to one side for now. The sockets on it are the older type and probably only tin plated contacts, so there is also a good chance they need replacing.

I think first step is to refit the links on the better cpu board and see if it still powers up. The eprom might need reprogramming after all these years but if I’m lucky thats all it needs.

Next steps would be to get a full keyboard working and a backplane. I still have the keyboard I last used, but the z80 board that I was using to decode the keyboard was not working last time I tried it, also possibly eprom. I didn’t have a programmer last time I tried and not sure I still have a software listing for it. It might be easier to build another keyboard.
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Old 5th Jan 2023, 10:59 pm   #6
locknut
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Default Re: Microtan 65 Restoration

Can't really add much, but following with great interest as I remember considering the Tangerine systems when I first started tinkering.

I've had success with dirty boards using hot water with detergent and a brush, followed by a good rinse... as said previously, some bits need to be removed and a spell in the oven is needed, until bone dry.
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Old 5th Jan 2023, 11:15 pm   #7
SiriusHardware
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Default Re: Microtan 65 Restoration

Quote:
The eprom might need reprogramming after all these years but if I’m lucky thats all it needs
Even if it's still good at the moment the chances are it's only a few years away from bit-rot so it wouldn't be a bad idea to read and over-programme it while it is still readable, to set the 'data fade' clock back to zero.
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Old 6th Jan 2023, 1:02 am   #8
Mark1960
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Default Re: Microtan 65 Restoration

I downloaded quite a few files from this link, which has a lot of Microtan 65 info and software.
http://www.microtan.ukpc.net/

I was going to try and get one of his backplanes, but the rack I have has card slides on 0.6 inch centres and I think the standard Microtan backplanes are 1 inch centres.
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Old 6th Jan 2023, 1:10 am   #9
Mark1960
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Default Re: Microtan 65 Restoration

Microtan pcbs are approx 114x205mm, I think this was called international cards and was an alternate to eurocards, which suits the rack I have, but it might not be easy to find a new rack with card guides for this size anymore.
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Old 6th Jan 2023, 10:24 am   #10
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Default Re: Microtan 65 Restoration

I had a Microtan 65 in the day and restored it about 10 years ago.
Sold it after I got it working.
Funds were tight, so I made as much as possible myself.
I used a second hand 19in rack, made a backplane using the Tangerine Diagram,
Wirewrap and perforated board. I Built a 10 amp ( or so ) power supply using the LM723 data sheet.
A friend who lived in Scotland gave me a disc drive, and driver card when he bought a PC , but it was missing the firmware eprom.
I had a paper listing of the data, and keyed in all 2k of data with only 1 mistake!
The MicroTan website was very useful with firmware and software.
Any software or tapes were recorded on my PC and played back to load on the microtan using the software “Audacity” Fewer errors!
The Tangerine users group sold eprom programmer , and eprom storage cards which worked well!
I learnt a lot from having the Microtan, which helped me move to Industrial Electronics from being in the TV trade!
Good Luck, all the paperwork and parts went to the new owner.
Phil Blundell
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Old 7th Jan 2023, 10:35 am   #11
Denis G4DWC
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Default Re: Microtan 65 Restoration

Looks like there's not many of us still owning a Tangerine system.

I built mine around 1981/2 initially with just the CPU board and a whole 512 bytes of RAM to program in machine code. With a cobbled together Hex Keypad I was hooked. It grew eventually into a Vero Rack with various other cards. I keep meaning to re-commission it and fortunately, unlike Mark1960's Processor PCB, my system has always been kept in the warm and dry.

An unsuitable Toroidal Transformer was rewound for the Power Supply with Wife holding the Toroid, me doing the threading and daughter, about three at the time, running up and down the lounge with the end of the wire

Machine Code was a really good learning experience and I soon bought and assembled the Tanex Board to give an amazing 7k of RAM plus Serial and Parallel ports and an assembler. At the time I think it was about £7.00 for each 1k of RAM (a pair of 2114 1k x 4bit static RAMs).

A Basic Interpreter followed with still more to learn.

Printers were well beyond my Hobby money but I did have a PO model 15 (Creed 444) Teleprinter I used to use for RTTY. The snag was that it didn't have a slashed Zero or Dollars symbol which made Assembler listings confusing at times so I wrote a routine to identify when a Zero was needed to be printed, remember it's position on the line then with just a carriage return and no Line feed step along the line and print an slash (Figures Shift X) across the 0. Same with the Dollar symbol by printing an S first. You never forget the noise and hot oil smell of a real teleprinter...

An Ascii Keyboard followed and I spent many late nights and very early mornings sat at the 6" green CRT display totally engrossed in various projects. By now I was flying. More Dynamic RAM was added using the Elektor Design for the Junior Computer. Initially, that just wouldn't work at all. With only a small 3" Telequipment scope on hand I made a 4 trace adaptor for it and managed to track down a timing problem. Now with 23k of Memory we were really, really flying.

At a rally some years later a guy had a stack of blank PCBs which I recognised as the Tangerine Processor board. I bought one and assembled another unit for a dedicated home House alarm. The boards hadn't been properly routed and had a track on a board edge partly removed and presumably why they were scrapped. An easy fix. I still have that board as well.

Storage was still just a Cassette tape at 300 Baud or 2400 Baud on a good day. The cost of Disk drives at the time was just too high. Hobby Money was way down the priority list particularly when the Mortgage interest rate went up to 17% on a house I could barely afford in the first place.

I think the Tangerine system was very underrated but was a brilliant learning tool.

After Moving house I went onto build the Wireless World Computer with a pair of 8" Floppy drives. More learning....

Denis
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Old 7th Jan 2023, 11:17 am   #12
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Default Re: Microtan 65 Restoration

Quote:
Originally Posted by Denis G4DWC View Post
... I went onto build the Wireless World Computer
Psi Comp 80 or SC84 Dennis? I still have my SC84 programmer from that era!
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Old 7th Jan 2023, 11:35 am   #13
Denis G4DWC
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Default Re: Microtan 65 Restoration

It was the SC84.
It was an interesting piece of kit but by then PCs were getting firmly established and then it sort of fizzled out..
I sold it all at a Rally several years go.
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Old 7th Jan 2023, 12:43 pm   #14
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Default Re: Microtan 65 Restoration

I like the look of the Microtan-R project described in the relevant section of the website Mark linked to in #8, where some of the original PCBs have been redesigned just enough to make them easier to build in the present without going too far away from the spirit of the originals, for example the use of fewer but larger capacity 'modern' RAMs and the use of EPROMs rather than PROMs to hold character generator code. Also the addition of a composite-out video connection on the CPU.

The only thing I have qualms about is the use of 2 x 16V8 GALs to simplify address decoding on TANEX-R card - I'm no fan of these since I noticed what a short life the manufacturer's own data sheets say the programmed data is likely to have. These could end up giving reproduction PCBs made today a shorter working life span than original PCBs from the late seventies.

I noticed another interesting project in that section as well, a PIC based PS/2 keyboard to parallel ASCII-out converter which could be pressed into service on all sorts of retro projects.

Last edited by SiriusHardware; 7th Jan 2023 at 12:50 pm.
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