The expansion unit has an RS232 board but its DC/DC converter had failed. I bought a replacement module and adapted it to the PCB layout.
Once it had power it was good to go.
Model I RS232
Author: Graham
Introduction
Why “jmp start ;microcomputers”? Well, ultimately it’s just a name. It sounds like “jump start”, but it’s also a pretty common line of assembly language. It’s a bit technical, but so is this site. I tried some AI names, but this came out of my head.
A microcomputer is a computer that is based on a microprocessor; a highly integrated processing unit that first appeared in the early 1970s. The term “microcomputer” was used a lot during this early adoption period but fell out of fashion by the early 1990s. Microcomputers are now referred to as PCs, notebooks, tablets, phones etc, so i use the term “microcomputer” as a shorthand for “vintage microcomputers” which are the subject of this site.
As i emerged from high school in the early eighties, microcomputers were the tech that everyone wanted, and this prompted me to enter the world of electronics. I got to play with several early machines, but there were so many that it was impossible to experience the gamut.
Over the last 8 years, i’ve had the opportunity to not just reacquaint myself with some familiar machines, including a couple i sequestered from those times, but also to experience many that i missed the first time around.
I’ve purchased many of my treasures through well known online marketplaces, but i have also acquired many from colleagues at the Adelaide Retro Computing Group – always at reasonable cost and often as generous gifts. I’ve tried to acknowledge significant gifts as i’ve added detail, but i apologise in advance if i have missed anyone.
I’m typically interested in workhorse machines but use the occasional game to demonstrate what a computer can do, or in many cases its limitations.
Making machines shine figuratively is my goal, including:
- Getting them working
- Getting them working again after they stop
- Adding software
- Adding accessories
- Connecting them
My machines are not pristine or mint – i aim for tidy and functional. I like them to be exercised regularly and standing by, ready to save mankind when the current tech collapses in upon itself like an abused CRT.
Generally i will try to make sure that machines are either original or can be readily taken back to original – and that includes modifications from, or typical of, the operating period.
I do compromise on hard disks; they are difficult to source and inherently unreliable. I never bin them, but i don’t think twice about replacing them with hard disk emulators. I also use disk emulators alongside original storage peripherals to make it easier to try, and to demonstrate, a greater range of software.
The purpose of this site is to:
- Show off some of my machines
- Make what i’ve learnt available to others
- Promote related local activities and groups
The info that i’m posting has been extracted from the notes that i have accumulated since 2017. Those notes were pretty rough and not always complete. Mostly i’ve rewritten them here, but their heritage still comes through in places.
My hobby relies on the amazing work that has been done by so many people to archive data – programs, disk images, data sheets, schematics, manuals, articles, photos, problems and solutions. I use these resources extensively, and i am grateful for them. I try to pay this forward by archiving disks and documentation to archive.org or other appropriate sites such as Microbee Technology.
Adelaide Retro Computing (ARC) Group
I started attending ARC Group meetups in about 2018 and have been a regular since then. This group has been a game changer for my hobby.
Some might describe retro computer collectors/operators/builders/gamers/hoarders as a little unusual, and numerous stereotypes are routinely rolled out. Many of us wear them as badges of honour.
Retro is a vague but inclusive term, and the group members and meet attendees reflect that diversity. This group is an opportunity for those people to meet in a friendly atmosphere to play games, show off builds, acquisitions, and restorations, and to talk bullshit about computers and life in general.
As a group, we have a lot of knowledge and skills that are of value to each other. There are many people with eyes on marketplaces, auctions, recycle bins, garage sales etc, so often group members are able to direct gear to the people with matching interests. The group is often a focus for downsizers etc, who are looking to clear cupboards and sheds.
If you’re in Adelaide and you have an interest in the retro computing world and adjacent interests, then come and have a look. The group meetups are the second Friday of each month. Check the facebook page for details.
Data Recovery
I have become familiar with tools for recovering files from floppy disks. I’m happy to help people recover important files from the past.
If you have files on 1.44MB 3.5″ floppy disks then just buy a USB drive, plug it into your PC, and copy the files.
If you are in Adelaide or thereabouts, and you have 720k 3.5″ disks, 5.25″ disks or 8″ disks that contain some important files, and you have had no joy with professional recovery services, then contact me and i’ll try my best to help.
Also, contact me if you have 5.25″ or 8″ disks that need a new home!
Commodore CBM 4016
- Commodore CBM 4016
- 4016 Arrival
- 4016 Case Stain Removal
- 4016 ROMs
- 4016 Keyboards
- 4016 Processor Boards
- 4016 Metalwork Unit 2
- 4016 Monitor 2 Clean & Reassembly
- 4016 Power Wiring Unit 2
- 4016 Reassembly of Unit 2
- 4016 Set to Work Unit 2
- 4016 Monitor 1 Clean & Reassembly
- 4016 Metalwork Unit 1
- 4016 Set to Work Unit 1
- 4016 Power Wiring Unit 1
- 4016 40 Column Downgrade
- 2031 Disk Drive & Running a Game on the 4016
I worked mainly on unit 2 first, so there is more detail on the process for that unit.
4016 Arrival
The Commodore PET (branded CBM in some markets) computer is an icon of early microcomputer history. There are very few in Australia and the only ones I have seen in South Australia was the one in the Adelaide Uni Physics labs back in 1983 and one imported from the UK. I am aware of one other that was for sale on gumtree about 5 years ago.
It was some surprise then that I spotted this image on facebook marketplace. I was further surprised when I contacted the seller and he said he had a second machine covered in pigeon poo.
Presentation is everything, so i was interested of course. We came to an arrangement for the first machine and i drove (with my wife for company) up to Snowtown (a town with a story) where it was located.
The site was an ex Telstra maintenance site, long since abandoned to the pigeons and probably a myriad of other undesirables. Just walking into the building was a health risk and the smell was unbelievable.
I paid a smaller sum for the filthiest computer ever, and another small donation got me a very disreputable 2031 disk drive. The other drive is not related to these machines.
I pondered my sanity as I put them on a drop sheet in the back of the car.
I do have some standards about what comes into my “clean” shed and both machines were well below the threshold, so they went into the “dirty” shed first.
Opening the covers proved confronting. The first was not too bad but very dirty and corroded. The second machine and the drive almost made me gag. They were full of some combination of pigeon fluff and pigeon manure, which I suspect just blew in over a long period. I donned rubber gloves and a face mask and began the ugly task of removing the debris, first in handfuls and then with the vacuum cleaner.
It was clear that I needed to disassemble the second machine and the drive unit if I was to get all of the offending material out – and that was a necessary first step to just being able to stomach and store the machines.
Having got most of the innards clear of crap, I started washing down the cases. This was an unpleasant task, but was not difficult. Pigeon mature seems to wash off fairly easily, and the largely plastic construction seems to have been unaffected by its coating. Some stains remained, and the metal parts had some corrosion, but I was happy with the improvement.
The second keyboard was set aside for the moment.
At this point the machines were allowed into the clean shed, although they were far from clean. Remarkably, though, they both seemed to be complete – not even a missing keycap. The condition of the mainboards was poor, though.
These machines are both model 4016-N which means that originally they would have had 16k of RAM and 40 column text.
They both seem to have been upgraded to 32k of RAM and 80 column text.
I thought initially that they must have been used by Telstra, and perhaps they were, but they clearly once belonged to TAFE.
These machines were produced late in the PET’s product life. They were obviously under cost pressure, eg there are a lot of places where rivets were used instead of screws.
80 columns is handy for things like word processing, but a lot of the games were produced for the 40 column models. It is possible to put the machines into a 40 column mode, but the characters are still narrow and the proportions changed.
These machines use universal boards so they can be reconfigured to 40 columns – this would require several links to be changed and a new edit ROM.
There was a lot to be done before any reconfiguration would be on the agenda.
4016 Case Stain Removal
Most of the stains came off by soaking with vinegar and then applying elbow grease.
4016 ROMs
Both boards have the same set of ROMs. Some of the ROMs on the first board are soldered in but all of the ROMs on the second board are socketed. The Proteus programmer was able to read the EPROMs, but the ROMs are a little more difficult. The program pin on the EPROM is a chip enable on the ROMs so it was necessary to make up an adapter socket for the ROMs to pull this pin high.
| Board | Type | Label | Socketed | Location | Address | Condition | Description | ||
| 2 | EPROM | Y | UD12 | 0x9000 | 36864 | -28672 | Word Processor | ||
| 2 | EPROM | Y | UD11 | 0xA000 | 40960 | -24576 | Toolkit / Extramon | ||
| 2 | ROM | 901465-23 | Y | UD10 | 0xB000 | 45056 | -20480 | Verified | Character ROM |
| 2 | ROM | 901465-20 | Y | UD9 | 0xC000 | 44152 | -16384 | Verified | Basic 4 |
| 2 | ROM | 901465-21 | Y | UD8 | 0xD000 | 53248 | -12288 | Verified | Basic 4 |
| 2 | EPROM | Unlabelled. | Y | UD7 | 0xE000 | 55344 | -8192 | Looks plausible but doesn’t exactly match any candidates | Probably an edit ROM of which there are many. |
| 2 | ROM | 901465-22 | Y | UD6 | 0xF000 | 61440 | -4096 | Verified | Kernal |
| 2 | ROM | 901447-10 | Y | Verified – file size is incorrect but data is good | 8 10 file size is incorrect but data is good | ||||
| 1 | ROM | Y | First 2k is the same as ROM 2 | Probably an edit ROM of which there are many. | |||||
| 1 | ROM | Y | Verified | Toolkit / Extramon | |||||
| 1 | ROM | Y | First 2k is the same as ROM 2 | Text Editor | |||||
| 1 | ROM | 901465-20 | N | Unknown | Basic 4 | ||||
| 1 | ROM | 901465-21 | N | Unknown | Basic 4 | ||||
| 1 | ROM | 901465-22 | N | Unknown | Kernel | ||||
| 1 | ROM | 901465-23 | N | Unknown | Basic 4 | ||||
| 1 | ROM | 901447-10 | N | First 2k is the same as ROM 2 | Character ROM |
4016 Keyboards
Process was (tedious):
- Remove the keyboard from the bottom of the computer cover.
- Remove the cable.
- Remove the metal clip grounding the foil cover to the keyboard.
- Wipe over the foil cover and set it aside.
- Blow out the keyboard.
- Remove the key caps with puller. The spacebar requires two sturdy pairs of long nose pliers
- Store springs.
- Wash keycaps in warm soapy water using a soft toothbrush to scrub and allow to dry.
- Once dry, wipe over once more with a damp cloth.
- Blow off the residual loose dirt from the keyboard assembly
- Desolder the caps lock switch.
- Remove the pcb screws.
- Clean the pcb with paper towel and IPA.
- Remove and store the caps lock switch (2 little levers).
- Store the barrels and keypads.
- Scrub the key frame in warm soapy water. Blow off and allow to dry.
- Wash the barrels in warm soapy water and allow to dry.
- Scrub the cable in warm soapy water, blow out, and allow to dry.
- Put the rubbers in a container and shake off as much dust as possible.
- Clean both sides of rubbers with cotton buds and IPA.
- Put the barrels back in the key frame and insert the rubbers.
- Clean them again.
- Re-coat rubbers with conductive coating.
- Inspect carefully for lint and remove.
- Reassemble.
- Test with harness and meter.
The conductive coating has to be mixed and then used within a couple of days so it makes sense to do both keyboards at the same time.
I did start with the second keyboard because it was in an awful state.
This is the first keyboard (from the cleaner machine).
The contacts were coated using a CircuitWorks Rubber Keypad Repair Kit. This kit is quite expensive and a bit laborious to apply, but it does the job. It looks like it’s using a silver paint. The key resistances were very low. There was enough in a kit to easily do the 140 or so keys.
The shift lock keys was not working. While looking for a replacement online I found a video where the author had worked out how to open the switch by twisting the terminals, so I thought it was worth having a look inside. It was filthy – I’m not sure how this much ick could get inside a switch with no significant orifice.
It was built like a puzzle. Cute little mechanism with lots of pieces. After a clean, things looked better.
There is a spring as well – fortunately it was still in the parts container!
It took a while to reassemble it. The pins screw through the contacts to create a hole and contacts at the same time. I added some aluminium foil to make sure the contact was still good. I was relieved to find that the switch was working.
Testing just requires a keyboard cable from the computer and a jig which joins all the columns to all the rows. Then each key can be tried. This can be done before putting all the key caps on by turning the keyboard upside down and pressing upwards. Otherwise, without the caps and springs, all the keys are activated at the same time.
4016 Processor Boards
Both cards have significant corrosion and were very dirty.
The process was as follows:
- Wash in soapy water. Scrub with toothbrush. Blow off and allow to dry.
- Inspect and gently remove socketed ICs (one had corroded on to a socket).
- Apply soapy vinegar, rinse.
- Apply soapy vinegar, rinse. Blow off and allow to dry.
- Apply de-oxit to corroded legs and leave for 24 hours.
- Clean legs with wire brush on Dremel.
- Clean with soapy water. Blow off and allow to dry.
Most ICs have oxidised legs. The legs on socketed ICs can be easily checked for integrity – in some cases, a small nudge was sufficient to make them fall off. It’s harder to check those that are directly soldered. It appears that in many cases the plating has been penetrated and is prone to flaking. I attempted to re-tin some ic legs, but the solder would not take even with lots of flux – I suspect the material required electroplating and that’s not happening. De-oxit is probably the only practical way to protect them. Of course, they could all be replaced, but that will be time-consuming and will risk damage to the PCB.
The MC3446 line drivers (for the IEEE-488 bus) are located near one of the case openings. One had legs corroded through. The others were in poor shape. They have been replaced with new ICs and sockets.
The PCBs are in generally good condition. The edge connectors had lost some plating, but the oxide has been removed with deoxit and the copper re-tinned.
On the second board, a damaged socket was replaced. I favour machined sockets, but this board never used them and the sockets that have been added in the past are either zero insertion force or dual wipe (the originals are probably single wipe).
The wire to the piezo was missing, so it has been replaced.
The configuration links in the middle of the board were untidy and used the wrong gauge wire. They have been replaced.
Other links have been made with wire wrap. The wires were unnecessarily long, making them vulnerable to breaking. The posts were too high, so they were prone to bending. The posts were cut down and the wire wrap redone.