Category Archives: Retro Tech

Motorola (Four Phase systems) S2000.

IMG_20150219_134721096This is a new one on me and a curious one at that. A quick search of the internet found a small piece on not a great deal and nothing on the company after they were sold to Motorola in 1981.

The machine we have here appears to be a small office machine; It has six serial ports on the back along with a 50 pin connector for an external disk drive. I’m guessing SCSI but I have no proof, I have no disk drive either.

IMG_20150219_134939086Inside the case is a card cage but it’s a bit stranger than it first appears. There seems to be two buses in the cage. The two boards on the left have card edge connectors and both have 6809 processors. The three boards on the right have three row connectors with pins that look like connectors on a VME bus. One board has a Motorola 68010. The other boards seem to be RAM cards.

When I power the machine up the fan whirs and I can see a couple of LEDs glowing optimistically. I don’t see any activity on the 25 way D type at the back labelled “J1 RS-232”.

IMG_20150219_134751888 IMG_20150219_135405795 IMG_20150219_135224395

Sharp MX-80A

IMG_20150210_184457251The Sharp MZ-80A is an all-in-one machine that’s of a style that was not unusual in the early 1980’s. Think Commodore PET, Intertec SuperBrain. Televideo TS-802 and 803. Even the humble Amstrad PCW range.

The screen Measures approximately 9″ diagonally and has a clear plastic plate in front of it. This is rather reflective as you can see in the above photo. The keyboard is full sized and the keys have a good degree of travel. There is also a number pad on the right.

A cassette recorder is built into the case along side the monitor and to its right. This records at 1200 baud (approx 120 characters per second).

IMG_20150210_184516815At the rear of the machine there is a figure 8 mains socket and rocker switch for power, the brightness and contrast knobs and a reset button.

Additional ports such as Centronics parallel and RS-232 serial are lacking though I believe they were available as an option. There is certainly space inside the case and the main board has an expansion connector heading off into the empty space at the back.

Rather unusually, it doesn’t have a resident BASIC interpreter. Instead there is a monitor ROM with very few commands and BASIC and other languages were available on cassette tape and loaded in as required.

Commodore 4032.

Pet4032-StartUpA friend at work, knowing that I was interested in retro computing, arrived one day with this splendid example of a Commodore 4032.. Sadly when I powered it up I only got a “Bingley beep” sound but there was at least some signs of life.

I moved around the board with a scope and found the clock looked good, as did the horizontal and vertical video signals.

More searching found that the _INT_ line to the 6502 was low. I reasoned that it should be mostly high. The 6520 PIA controller driving the IEEE port is connected to that line and as I didn’t need IEEE at the moment I pulled the chip out. Power up and Bingo! now running.Pet4032-J7-pin5


I replaced the 6520 and all is now well.


What about disk drives? Fingers crossed. Switch on.

Having read through a few hastily translated bits of the technical reference manual I felt that I knew enough to try and get the floppy drives connected. I wasn’t given an original cable but looking around the back of the card cage and at the drives themselves it looked likely that they needed a 25 Way cable (the manual didn’t say).

9a791ae12125cd64d6d05ccf2225dd3aPowering up the
drives without the cable seemed OK though they did sit spinning. 5 1/4 drives don’t
start until they are needed (usually) but I don’t know what 8 inch drives generally

Switched everything off. Plugged in a cable. Disks on. Main unit

Drive light comes on for a bit and then goes off. Whoopee.

This is repeatable 🙂 I have since tried a floopy in the drive and get
the same behaviour. I can’t get it to boot but I’m delighted to have got it this


A better boot.

06deb3285e7f43917474be0687d2ae7dIn the previous post I got the PDP-11 booting from a tape emulator into the diagnostic system, XXDP.

Next I wanted to move on a bit.

I was given some boxes of RX50 diskettes by a friend of mine. DEC kit can be very picky about floppies and generally wants them pre-formatted. The PDP-11 is no exception. It is possible to format them on a PC I believe but I don’t have a PC with a 5.25″ floppy drive.

I booted the PDP into XXDP and then used that to initialise a floppy diskette. this doesn’t format it, just writes some structure to it.

I next used the COPY/BOOT and COPY/FILES commands to make the diskette bootable and have all of the files that are on the tape.

I now have a bootable floppy 🙂

First boot.

I was a complete novice with the PDP-11 and so I asked for some help on the forums. Thanks to the help of the folks there I got the machine to boot.


This is what I did…

Downloaded the TU58 emulator from Don’s site here. This enables a PC to emulate a TU58 which is a tape drive unit that talks to the PDP using a serial port.
I downloaded a disk image for the TU58 emulator to load and present to the PDP when asked, from here.

I used Win Xp on my rather old laptop and used Hyperterm on COM1 (19200) to act as my terminal to the PDP.
I started a command prompt on Xp and then started tu58em with the options -p5 -s 9600 -r 11xxdp.dsk. This starts tu58em talking on COM5 at 9600 baud with the disk image mounted as read only.

I had COM1 connected to the console port and COM5 to the printer port.

I started the PDP, watched it go thorough its self test and the numbers 1 to 9 and when it started rattling the RX50 I pressed ctrl-C to break the boot. It asked for a command and I used…


and watched as it started up.

One point I didn’t pick up on until I saw it was that it has both DD0 and DD1 are on the same port. I thought they would be on two serial lines (SLU) and they are not

Now I’ve booted up the PDP I’ll sit down with the manuals and boot myself.

PDP-11/53 – Overview



I picked up this PDP-11/53 in Feb 2014. You can read a little about it here.


Somewhat unorthodox to say the least but strangely practical. It appears that a previous owner has taken the card cage from a DEC chassis such as a BA-23 and mounted it in a 19″ cabinet. There is space above the card cage for a couple of full-height 5.25″ drives.

06deb3285e7f43917474be0687d2ae7dAt the back.

I haven’t followed the internal wiring through yet and so I haven’t found out why there are two mains sockets. When I run the machine I connect to the socket on the main PSU and use the switch on the back.

The card cage is completely exposed as you can see. Currently there is plenty of space for expansion.

Above the card cage is the space of drives and to the left of that an aluminium plate with 2, 25 way serial connectors. These are connected to the two serial ports on the processor board. One for the console the other is labelled “Printer” but is a general SIO. These are known as SLU0 and SLU1.

The Cards.

My machine has the following cards…

  • M7554 – CPU – KDJ11-DA Q J11 CPU 15MHz, 512-Kbyte RAM, 2 SLUs, LTC
  • M7551 – CA – Memory – MSV11-QC Q 4-Mbyte 22-bit parity/CSR MOS RAM
  • M7555 – Disk controller – RQDX3 Q MFM Winchester and floppy disk controller (RX50/RX33/RD50-54/RD31/RD32/RD33)
  • M7516 – Ethernet – DELQA-M Q Ethernet interface (replaces DEQNA)
  • M7546 – TK50 – TQK50-AA Q TMSCP controller for TK50 tape unit.



PDP-11/53 – Introduction


The beginning

Towards the end of 2013 I started to think getting hold of a PDP11 of some form might be fun. I know there are excellent emulators out there but nothing is the same as actually using the real thing. It’s partly the “getting”. It’s partly the intangibles. Flicking the power switch and hearing the clunk of the switch, maybe relays, the fan. Watching the self test go through for the first time. On an emulator it will pass. On the real machine it might not. All or these things and more make me want to use a real computer rather than an emulator.

That’s not to say I won’t use an emulator. Let’s be pragmatic here. I’m sure as I write this that one will be an important part of getting the PDP-11 up and running. The easiest way of migrating files between different disk and tape formats seems to be to use an emulator such as SIMH.


Where to begin?

I am a long time fan of the Vintage Computer Forum and also the CCtalk mailing list. Every now and then something will come along on one of these two sources. Every six months to a year, someone’s collection will reach “critical mass” and they reach the point where a major clear out is needed. In the last few of these I’ve read about, the people concerned has accumulated large amounts of “Big Iron” and it seems as if they were just at the right place at the right time to get shed loads of stuff given to them.

So it seems with my PDP.

I saw a posting from someone with an industrial unit full of piles of stuff, Sinclair, BBC, Atari, etc. etc. and so on. There were a couple of things on my wish-list and so I got rid of a few pieces in my collection to make space and raise some funds and set off on a bit of a road trip.

I’d already inquired about the possibility of a PDP-11 but it was not my primary mission but when I got there and saw piles and piles of stuff it became clear that I’d probably have a DEC in the boot when I left.



A Harmonium.

Many years ago I sat down to watch a film on video (remember VHS tapes?) and as was customary there was a number of trailers advertising other films “coming soon”. One that stuck in my mind was for “She’s having a baby” (IIRC) some light hearted rom-com type thing. The reason it stuck in my mind was nothing to do with the film itself but the music running underneath all of the action.

It was a chirpy concertina-y piece I hadn’t heard before. I didn’t find out what it was for years until I was watching “Later… With Jools Holland” and it was there, in the middle of a medley of tunes. Jools commented that the music had a “Penguin Café” bit in the middle and the chase was on.

I scoured the place for “Penguin Café” and found my missing music. It was called “Music for a found harmonium” and the instrument of choice was indeed a harmonium. Of course these days Wikipedia is you friend

Since that first hearing I have wanted to have a ride on a harmonium.

But what is it?

For those that don’t know, a harmonium has a piano keyboard, Bellows from an organ and the workings of a mouth organ inside.

They come in two sizes really; “Piano” or “Sewing machine”. There was no way I wanted a piano sized item and even the small, desk top ones are really too expensive for a non-piano player to justify out of the spending money budget.

A nearly found harmonium.

Enter the local car boot sale. This has become too tempting of late and although I don’t often buy more than the weekly vegetables I am always on the lookout for something interesting, especially old computers for my collection.

There haven’t been any of those lately but “Swipe me” there was a Harmonium on one of the stalls. I wasn’t looking for one as such but you shouldn’t look a gift horse in the mouth so I got it.

Now, this item was previously owned by some arts centre and had seen a lot of action. The con-rods on the stops (note the technical terms) were all bent. A large number of the springs that make the keys return were bent. The bellows leaked and had been repaired with masking tape but after straightening the springs and putting them back, a quick pump of the bellows and that familiar sound came out. Yippee.

A quick look at the photos will show you just how much “life” it’s seen. A closer look at the internal shots will show that this probably isn’t a top spec instrument anyway but boy it’s fun.

A bit of a repair job.

Having looked over the instrument I wasn’t going to try for a restoration. Everywhere I looked there was damage. If I replaced everything that was damaged there would be nothing left. So instead I decided to make it work properly.


bcd937ac3932dd381d2424694a402055The original bellows were made from stout cardboard with some kind of kid leather over the joints. I took the old ones to pieces and copied the shapes onto some more stout card that I had stored for just such an occasion. I didn’t have any leather but I did have some neoprene covered nylon that I use for the skirt segments on the hovercraft so I used that.

Several hours and two tubes of impact adhesive later the job was done.


One of the handles was smashed and so I bought a couple of nice brass handles from eBay.




380Z entering a hiatus…

The progress has been a bit slow on the 380Z front at the moment.

As you may have read, It displays nonsense on the screen and doesn’t do much else. I wondered if this was just a fault with the display controller card or more. At startup the machine is supposed to display a boot prompt and wait for a key press. however, I don’t have a keyboard. The keyboard interface is a simple parallel port with 8 bits for the decoded key code and a strobe to say that the data is ready. To try and make some progress I made a simple one key keyboard built into a 15 way connector.

All it does is permanently tie the lines needed to send a ‘b’ and then it has a push button on the strobe line. I push the button and the 380Z thinks I’ve pressed a ‘b’.


This didn’t change anything and so I think the problem is more with the logic board.



It has been suggested that the ROMS (EPROMS) might have lost their memory. I think their original life expectancy was only about 10 years and we’re way past that now. I would like to read them and compare them with the image files that I have. The chips used are TMS-2716, 2kx x8-bit EPROM from Texas Instruments. Their power requirements are the same as the 2708s and different to non-TI 2716s. I have been able to borrow an EPROM programmer and I have the needed adapter on order from the USA but unfortunately the seller has had some problems with his supplier and it’s taking longer than I had hoped.

When it gets here I’ll be on the case.