+- Discussion Forum for all things Microbee (https://microbeetechnology.com.au/forum)
+-- Forum: Microbee Forum (https://microbeetechnology.com.au/forum/forum-1.html)
+--- Forum: Microbee Hardware (https://microbeetechnology.com.au/forum/forum-6.html)
+--- Thread: Restoration of a Microbee II - where to begin? (/thread-1046.html)
Restoration of a Microbee II - where to begin? - headwerkn - 08-07-2026
Hi all,
A couple of year's back I was given a pair of Microbees by a former workmate, who'd used them for his electrical engineering degree back in the late 1980s and early 1990s. "Pair" is being generous - more like 1.75 units, as you'll soon understand why. Anyhoo, they've sat waiting patiently since then as I finished up my own electrical engineering degree (now complete, thankfully) and I now have some spare time to start the restoration process.
I'm hoping to use this thread to gather information for how to approach a careful and considered restoration, to get at least the better of the two machines up and running reliably and keep it that way, one that won't unduly risk a system which by all accounts is getting harder to find. I'm reasonably confident and capable with basic electronics, soldering and troubleshooting (a child of Dick Smith's Funway Into Electronics) with mostly audio amps and the like (solid state and valve) but haven't had a lot of experience with serious board-level restoration of computer hardware or digital systems, old or new. The lack of SMD in Microbees is reassuring, to say the least. I've spent many hours watching the likes of Colin @ ThisDoesNotCompute and various others go through the process on various systems, so have a rough idea of what I'm in for.
Along with the "two" systems I've also been given a period-correct (though non-Microbee-branded) Kaga 12" green monochrome monitor, one and a half power supplies (2 harnesses, 1 transformer), a completed EPROM reader/writer kit and a nice bundle of documentation.
At this stage I've resisted any urge to apply power to anything "just to see", lest I make it worse ;-)
Both systems have 'Model II' on the case. The first system appears intact and unmolested, just a bit dirty and yellowed as you'd expect, shows MB1732-33 ©1983 on the core board and from what I can tell has a full complement of ROMs, and no expansion slot soldered in. From what I can gather from the Wiki, this is a standard 32Kb Series 3 based on the case badging?
The only damage I can see is a broken 9V battery clip lead. The big 4700uF cap is the only electrolytic I'm seeing; no doubt it'll need replacement however it doesn't appear to have caused any corrosion nearby. Looks like the rest of the board is ceramics/tantalums only, bless whomever did the original design and BOM ;-)
Keyboard is an unknown quantity at this stage, by the sounds of things replacement is likely, but all the key caps are in place at least and they're not too gungy.
The other system is, umm... well, let's say, it's seen some things ;-)
Both Core and Main boards show plenty of modification and damage (bent pins etc). Exactly what's going on here is beyond my current knowledge... doesn't seem like factory modification/upgrades, more the efforts of a well meaning psychopath with a soldering iron. This was evidently the unit that was used with the EPROM reader, whether the modifications were required to support that peripheral, maybe?
Based on the "vented" top case logo it's apparently a PC85, 64K CIAB or SBC. A sticker on the missing keyboard surround might help. Board codes are PN1632 RevD for the Core and PN1248 for the Main which I'm reading the Wiki correctly indicate an earlier standard model though? Suspect this system might have started life as a bit of a bitsa, and was subsequently abused accordingly.
Suffice to say it's a mess and quite possibly beyond repair - certainly not without a tonne of work. A number of components seem to be damaged and just getting the Core board to mount would require a plenty of time with a pair of pliers to straighten the interface pins. The board appears to have a decent wad of RAM installed but is missing ROMs? Keyboard is down a few keys too. Likely only good for parts, but we'll get the other unit working first then decide if there's anything that can be done for this one.
The monitor is a Kaga KG-12NA-N. I've managed to find some resources online including a good general reconditioning video including recapping and cleaning out the V/H-HOLD pots. Other than being very dusty internally, it seems fine with no visible burn-in, though someone appears to have bypassed the Power On/Off switch for, uh, some reason. I think a careful cleaning and possibly some recapping will have it running without too much drama.
The power supply transformer and associated cabling do not inspire confidence. When I get a free moment I'll do some quick tests with a multimeter to check output and continuity, but honestly I'm inclined to just give Ewan some money and get a whole new supply and cable kit when they become available.
So with all that, I'm curious as to what's considered the best plan of attack by the community for restoring old Bees? As it stands, my general plan with the 'good' unit is:
- Take everything apart, at least to a manageable level.
- Give the PC boards a thorough clean with IPA and a soft brush.
- Replace and resolder the broken 9V battery clip.
- Sort out a dependable power supply and cable set (new or clean up existing).
- Give all the plastics etc. a good clean. (Not interested in retrobrighting.)
- Give the monitor internals a thorough clean, attempt power up, recap as necessary.
- Power up and take it from there. Sounds like keyboard issues are a near-given.
Any other suggestions?
Also, I'm guessing a Gotek is the preferred/least complicated way to get programs and data in and out of the Microbee in this day and age? I do have a potentially usable cassette unit (great big Sony unit used for controlling slide projectors) but honestly cassette-based data storage is something I genuinely hated in the 1980s and early 1990s and have zero nostalgia for ;-)
Many thanks if you've read this far - looking forward to people's suggestions and wisdom!
Cheers, Ben.
RE: Restoration of a Microbee II - where to begin? - CheshireNoir - 08-07-2026
Whoah! A lot going on there.
OK just some quick thoughts off the top of my head:
1) That's not a 9V battery holder. It's for the battery backed up SRAM and uses a special type of battery. (I have one Core board like that somewhere in my stash). It's apparently a camera battery and supplied 4.5V.
2) Neither unit has a DRAM / Floppydrive "Core" board so Gotek is out for now. Not the end of the world. You can either get a new Core board or just stick to tape input. (This is how I ran my machines before I flipped one of my SRAM Core boards out for a DRAM Core board.) I have found playing back audio files from an old smartphone takes a bit of effort to get the volume dialled in but otherwise works fine.
3) The switch on the monitor has probably failed. A lot from that era have. (Commodore monitors of that era are particularly notorious for it)
4) Just really be careful if you decide to work in the monitor. Even if off, the tubes can reaccumulate a charge and they are not fun if you accidentally short them. I used to service CRTs for a living and they still scare me.
5) That's a GREAT bundle of documentation there!
6) I'd love to know what all the mods to the second core board are for. I'm guessing something to do with all the RAM in there.
Cheers!
John
RE: Restoration of a Microbee II - where to begin? - headwerkn - 08-07-2026
Hi John, thank you for your reply.
Quote:1) That's not a 9V battery holder. It's for the battery backed up SRAM and uses a special type of battery. (I have one Core board like that somewhere in my stash). It's apparently a camera battery and supplied 4.5V.
Well that explains why each terminal is seperate, hehe.
Quote:2) Neither unit has a DRAM / Floppydrive "Core" board so Gotek is out for now. Not the end of the world. You can either get a new Core board or just stick to tape input. (This is how I ran my machines before I flipped one of my SRAM Core boards out for a DRAM Core board.) I have found playing back audio files from an old smartphone takes a bit of effort to get the volume dialled in but otherwise works fine.
OK, good to know. I'd wondered if any app developers had produced 'cassette' apps for iOS et. al. that can audibly play data tape files for use in old 8 bit systems.
Quote:3) The switch on the monitor has probably failed. A lot from that era have. (Commodore monitors of that era are particularly notorious for it)
4) Just really be careful if you decide to work in the monitor. Even if off, the tubes can reaccumulate a charge and they are not fun if you accidentally short them. I used to service CRTs for a living and they still scare me.
Makes sense. Yep, am aware of how to discharge a CRT anode and still have a pair of old kangaroo leather motorcycle gloves that I'd wear when working on live tube guitar amps ;-) The fragility of CRTs does bother me a little. I'm kinda hopeful it powers on file and I can just get away with a hearty blast of compressed air to clean the innards.
Quote:5) That's a GREAT bundle of documentation there!
It is quite a bit! I think the Repository already has everything I have, but if I come across anything not covered I'll be sure to scan it and make it available.
Quote:6) I'd love to know what all the mods to the second core board are for. I'm guessing something to do with all the RAM in there.
Me too! The modifications seem rather extensive, across both boards. I'll see if I can get hold of the previous owner (he left our company a couple of years ago) and find out more.
Hi John, thank you for your reply.
Quote:1) That's not a 9V battery holder. It's for the battery backed up SRAM and uses a special type of battery. (I have one Core board like that somewhere in my stash). It's apparently a camera battery and supplied 4.5V.
Well that explains why each terminal is seperate, hehe.
Quote:2) Neither unit has a DRAM / Floppydrive "Core" board so Gotek is out for now. Not the end of the world. You can either get a new Core board or just stick to tape input. (This is how I ran my machines before I flipped one of my SRAM Core boards out for a DRAM Core board.) I have found playing back audio files from an old smartphone takes a bit of effort to get the volume dialled in but otherwise works fine.
OK, good to know. I'd wondered if any app developers had produced 'cassette' apps for iOS et. al. that can audibly play data tape files for use in old 8 bit systems.
Quote:3) The switch on the monitor has probably failed. A lot from that era have. (Commodore monitors of that era are particularly notorious for it)
4) Just really be careful if you decide to work in the monitor. Even if off, the tubes can reaccumulate a charge and they are not fun if you accidentally short them. I used to service CRTs for a living and they still scare me.
Makes sense. Yep, am aware of how to discharge a CRT anode and still have a pair of old kangaroo leather motorcycle gloves that I'd wear when working on live tube guitar amps ;-) The fragility of CRTs does bother me a little. I'm kinda hopeful it powers on file and I can just get away with a hearty blast of compressed air to clean the innards.
Quote:5) That's a GREAT bundle of documentation there!
It is quite a bit! I think the Repository already has everything I have, but if I come across anything not covered I'll be sure to scan it and make it available.
Quote:6) I'd love to know what all the mods to the second core board are for. I'm guessing something to do with all the RAM in there.
Me too! The modifications seem rather extensive, across both boards. I'll see if I can get hold of the previous owner (he left our company a couple of years ago) and find out more.
RE: Restoration of a Microbee II - where to begin? - headwerkn - 06-08-2026
An update.
So the existing, complete power supply and cable harness was tested to see if it still worked - and was showing +15VDC. That seemed rather higher than the 9-12VDC suggested, so as soon as the new power supplies became available I put in my order.
For all my "take it slowly" approach mentioned earlier, curiosity got the better of me... plugged everything in, switched the power on and the Microbee suddenly gave a very confident beep. Decided to throw all caution to the wind (though a fire extinguisher was standing by) and fire up the monitor... which resulted in neither fire nor smoke, but an illuminated RED LED and a flickering, rolling display. After about five minutes of fiddling with the various controls I managed to set a stabilised, somewhat centred image. So far so good...
.... and surprise surprise, the keyboard is having issues. Most of the "centre" keys either worked from the off, or started working with some repeated attention, but pretty well all the "outer" keys are dead. Suffice it to say, that's put the brakes on further testing.
Currently the "standard" keyboard replacement kit is out of stock. Is it worth attempting to pull apart and clean/fix the existing switches? Or just wait out until the kits become available again?
RE: Restoration of a Microbee II - where to begin? - ChickenMan - 06-08-2026
Great to see its up and running, well partly. The video is displaced and should be at the top of the screen, not in the middle.
Personally, I'd clean the few "essential" keys that are not working and wait for a keyboard replacement when back in stock.
RE: Restoration of a Microbee II - where to begin? - MbeeTech - 06-08-2026
I just checked and I have the bits on stock to make up a couple of keyboard kits.
I'll update the qty's in the web store, and you can secure yourself a kit.
It is always best to email if you want something that is out of stock, otherwise it flies under the radar as we are really busy
with assembly & design services work most of the time.
RE: Restoration of a Microbee II - where to begin? - headwerkn - 11-08-2026
(06-08-2026, 06:20 PM)MbeeTech Wrote: I just checked and I have the bits on stock to make up a couple of keyboard kits.
Thanks Ewan, ordered a replacement kit. Given several other functional keys are a bit 'dicky' I think I'd rather renew the lot in one hit.
(06-08-2026, 05:22 PM)ChickenMan Wrote: The video is displaced and should be at the top of the screen, not in the middle.
Thanks. I had another play around and managed to get things displaying properly. I also managed to load up Word-BEE from ROM by typing 'pak' ("1" key doesn't work so I was surprised this worked) which was rather exciting.
Will have to read the manual and figure out how to drive it. The last time I did word processing in a text-only editor was in 1993 on a BBC Model B :-p