Ohio Superboard build (Compukit UK101)
OK, this is going to be a long project to build a replica of the 1980's Ohio Superboard single board computer with maybe a few mods along the way, see how I feel.
A nice new PCB. A quick check of stock and it looks like I have most if not all the parts needed.
The plan is to fit Cherry MX key switches from an old keyboard too.
Really looking forward to this one as I built the original Compukit UK101 way back in 1980 and had it for a few years before it was replaced with the BBC Computer, but I do regret giving it away as it was my first 'real' computer, my actual first micro was the MK14.
The plan is to fit Cherry MX key switches from an old keyboard too.
Really looking forward to this one as I built the original Compukit UK101 way back in 1980 and had it for a few years before it was replaced with the BBC Computer, but I do regret giving it away as it was my first 'real' computer, my actual first micro was the MK14.
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This build was based on the Klyball replica board of the original revision D 1980 variant.
A bit challenging as there was no solder mask or silkscreen printing done, this made the construction manual very useful. Care needed to be taken at all times as without a solder mask solder bridges were easy to make. particularly under the IC sockets. There were a few notable modifications from the original, the keyboard was redesigned to accept Cherry switches and the ROM sockets pre wired to accept EPROMs. |
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First job was to install all the IC sockets, I chose turned pin for 2 reasons, I liked the quality but most importantly they do not sit flush with the board so it was possible to visually check for solder bridges as I went along. Important note: all the sockets are upside down, remember this if you are fault finding / installing IC's!
Decoupling capacitors and passive components fitted next. The instructions did not include the optional RS232 components but I fitted them anyway |
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I used Cherry Red switches and low profile keytops taken from an old keyboard, the incorrect tops were sanded off and relettered with letraset then sprayed over with matt varnish. The old keyboard came with a prepressed mounting frame, so I used this to align all the keys. (Sorry Ian, I know you said to use a very specific keyswitch but I was building this effectively free of charge as I already had all the parts). I moved the 'RESET' switch from right next to the Return key to the bottom left of the keyboard and duplicated it so it now required 2 fingers to reset. I also found a locking switch, so added this at the bottom for Caps Lock. |
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A bit of a leap forward here... I also fitted the extra power supply caps along with a discharge resistor as the capacitor was on the PSU side of the fuse. I also made a daughter board to hold; Power, Cassette In/Out, and video, leaving J2 available for other types of connection. J1 was prewired as a Cassette configuration. Then all IC's were fitted, they were all tested in the Retro Chip Tester Pro beforehand. For the ROMs I used 28C16 EEPROMS, with BASIC 1 & 3 being the 'fixed' versions, and I decided on the CEGMON C1 for the OS |
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After carrying out the normal power supply tests, etc, it powered up first time, though I could not get the monitor to lock on, the problem was the rather new LG type monitor, when I connected it up to my wall mounted Sharp monitor all was well. There were a few minor glitches occurring, crashes, graphic noise, etc. I decided to swap all the non LS series IC's out for LS variants, so now the entire board is built on 74LS, this cleared up all the issues in one go. It is of course possible that one or more of the older no LS were 'misbehaving' despite testing OK. |
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The first mod was to increase the working RAM. I have the 610 board ready to be built but decided on a quicker fix, moving the 6502 up onto a carrier board and adding a CY7C199 32k RAM directly on the BUS, I did consider having a board made up but to be honest wirewrap is easy and fast and the entire wrap took less that an hour. I recovered the old 2114's from the main board. I treated the daughterboard with silicone conformant sealer, normally I would do this to the main board as well but refrained in this case further mods needed be done in due course. Because no mods were done to the board for this it is possible to revert to original simply by removing the daughter board, relocating the 6502 back in the main board and reinstalling the 2114's which will be packaged with the Superboard.
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The power on reset was next (as it didn't come with any!), I used a DS1813 reset chip, the +5v and ground were easily available at W1, with the reset line appearing close by. Note: I used to cover modifications with green soldermask, though have recently decided to switch to 'red' to make it more obvious where a mod has been done. I found that the best way to cure solder mask is; after application pre heat it (300C) then apply the UV light for about 5 minutes. |
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Time to mount the board, I am using 5mm Aluminium sheet, probably did not need it to be this thick but I had this in store, it actually weighs more than the Superboard! There are lots of holes because I decided that if the PCB had a hole, it was getting a mounting pillar! I went for a clear top plate just to protect the board a little, made from 5mm acrylic it could in theory support a monitor. |
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A full memory test was completed of all 32k
The cassette port was tested at 300Bd; Works with my Sony TC-134 deck, works with an old 1980's Crown cassette player, BUT doesn't work at all with a modern cheap cassette recorder, when I look at the output waveforms of the modern player they are very distorted. This fits with what other people hade said about the modern players, so I am not too worried about this. There does seem to be a severe shortage of audio files online with programs for this machine. However there are libraries of plain text files that can be loaded via the serial port, this is where I went next. |
I made up a complete set of cables, audio, video, power, etc. to be stored with the system so I don't have to hunt around should I ever get it back out of storage again!
I removed the cassette configuration plug and made up a serial cable. Wiring as 1200Bd,8,N,1 and connected this to my PC via a USB/Serial adapter. I loaded and saved several files with no issues at all, so this is my goto in the future. Using TeraTerm: 1200,8,N,1 5mS-chr delay, 100mS-line delay Superboard to PC PC-Superboard S: Save<CR> S: LOAD<CR> PC: File:Log PC: Send File............... S: LIST<CR>.......<space><CR> S: <space><CR> PC: Stop Logging |