Category Archives: Post Increment

Gotek Disk Images

Here are the disk images I use for some of my vintage computers.

These are intended for use with the excellent HxC2001 firmware. The HFE format should work with the standard Gotek firmwre but I have not tried that personally.

Microbee – double sided 40 track

Kaypro IV – double sided 40 track

Kaypro II – single sided 40 track. Note that the Gotek will need to be configured to ignore the side select signal.

Buying a Microbee

I recently purchased a large cache of Microbee computers with the intent of refurbishing them and reselling to the retro computer community.

I’m working my way through them, and there has been a lot of interest from people who are eager to buy.

Right now, the Microbee base units are $400AUD, and monitors are $AUD200. This does not include post and packaging, if required.

NOTE: parts have arrived from China and I am slowly working through upgrading and testing disk systems. There are a small number of ROM systems still available.

NOTE: all of the remaining systems have cases engraved with “Lisarow High School”. I can send pictures of the cases before you agree to purchase.

The price may change depending on the number of parts I need to make them work.

If you still interested, here what you need to know:

  • The systems are tested and working. DRAM has passed a memory test, video is stable, and floppy controllers (if fitted) are aligned using a Gotek floppy drive emulator.
  • The keyswitches will probably need cleaning, so not all keys may work correctly. You will need to clean then (excellent instructions from Ewan Wordsworth of Microbee Technology can be found here), or you can buy a full keyboard replacement kit from www.microbeetechnology.com.au
  • The systems do NOT include a cable or power supply. These can be purchased from www.microbeetechnology.com.au
  • The 128k Microbee systems do NOT include a floppy drive, unless otherwise stated. I do have a few 3.5″ drives that could be used to make up a Computer-In-A-Book, but I’ve not had time to refurbish them so far.
  • Monitors are not included, unless otherwise stated. I do have a few amber Microbee-branded monitors available. Once they are gone, they are gone! Monitors have all been sold!
  • Cases will be wiped clean and any writing or non-original stickers will be removed. The cases and keyswitches may be yellowed from age or sun exposure. Some cases may be engraved by the orignal owner (apparently many of these systems came from “Lisarow High School”).
  • If the case is engraved, I will confirm with you before payment is accepted.
  • There are a few ROM based systems available. If you want one, please contact me at craig@postincrement.com for exact details on availability.
    Note that ROM systems cannot be upgraded to a disk system without a replacement coreboard and maybe some baseboards mods. I may have some floppy coreboards available at a later date.
A “hive” of Microbees?
A 32k ROM Microbee showing the BASIC prompt

System-80 working (sort of)

This poor System 80 has been subject to cruel and unusual punishment at the hands of previous owners.

I’ve got the Ready prompt (the equivalent of the TRS-80 Memory Size) but it’s been hard work. All of the 2102 video RAMs needed replacing, as well as several LS157 muxes. I managed to link A4 and A5 when replacing a mux – that cost me a few days.

Pressing Enter gives a screen of full graphics blocks – I think the video RAM read is not working fully. But to debug that, I need to understand what is left of a lower case support mod and (I think) software switch for 32 col mode

Restoring the System-80

The battle for the System 80 has begun!

I started with no video, no CPU activity, and a very bodgy looking 64k DRAM upgrade using 4164s

Fixed the CPU issue by replacing a dead electrolytic in the reset circuit. Video came back when I replaced the cable between the boards.

I’ve reversed the 4164 upgrade and am working on the Drastik.

The time honoured “ROM of NOP” is generating square waves on the lower 8 address lines. Now I need to find where they stop being square!

Drasktik working on Model 1

Success!

The Model 1 is reporting 48k memory without a DRAM in sight. Only two solder wires required, plus adjustments to the two sets of jumper pads which I have replaced with DIP switches for ease of testing.

I’m still working on the solder-less 16k upgrade. May not be possible. Will look at this tomorrow (maybe).

Two minor issues with the board. Seems I can demux 14 bit DRAM addresses but have forgotten how NOR gates work. 🙂

Also had to rewire the keyboard cable as the janky job performed by the previous owner died when I opened the case.

I’ve also 3D printed some replacements for the rubber-ish board standoffs that crumbled to dust when I flattened the boards. If anyone wants the files, let me know.

Conquering the Alps

The collective wisdom of the Internet comes to the rescue.

TRS-80 owners on the TRS-80 Model 1-4/4P Facebook group offers many suggestions to my keyswitch dilemma, including replating the contacts, applying conductive paint, and adhesive copper.

One suggestion stood out – not only because of it’s simplicity but because I have used it many times myself over the years. This procedure requires a very special tool, one that is nearly obsolete in this day and age. I wasn’t sure I had such a rare device.

I did find one, eventually, in the back of a drawer

The rare and timorous beastie

The mighty pencil eraser, handily attached to it’s applicator wand.

A few quick pokes on the offending contacts, and the resistance dropped to below 1k in most cases. In an hour so, all of the key switches had been reassembled and resoldered.

I did look at the contacts under the microscope but didn’t see anything significant. Perhaps the gold looked a little brighter, but that’s hard to tell on an $80 microscope with 1080p screen that is three inches across 🙂

We’ll see how long the fix lasts, but for now, I am declaring victory.