This repair has been on the to do list for ages, so let’s finally get to it!
In my mind, Tektronix is a brand that makes electronics lab equipment like oscilloscopes and logic analyzers. Turns out, they made quite a few terminals and a couple of computers! A good friend saw this one for sale local to him, and I poked him till he agreed on picking it up for me.
Picking it up may be the wrong wording, this thing is big and heavy! It weights about 35kg and it’s nearly a meter long!
So let’s have a look at what this is, what I needed to do to repair it and what it can do!
Some history
The machine I got is a Tektronix 4051 graphics workstation, released in 1975, but let’s look a bit at the history from Tektronix before this was released. Tektronix started in late 1945 as Tekrad, but quickly got renamed to Tektronix. One of their first products was the 511 oscilloscope, the first oscilloscope with a trigger!
This turned out to be a good thing, and soon enough, Tektronix was synonymous with oscilloscopes and known as a company that made some of the best test and measurement equipment. In the 60s, mainframe and then minicomputers became more popular, which often needed a terminal. Tektronix at this point was making storage oscilloscopes, which use a storage CRT tube that can “remember” drawn signals. Using this technology, Tektronix released their first terminal in 1969, the 4002. A 11″ terminal that was capable of displaying graphics with a 400×300 pixel resolution. As the CRT rememebers the drawn data, there was no need for a RAM framebuffer!
A few years later in 1971 they released the 4010, again 11″ but now with 1024*780 pixel resolution. As they used Storage CRTs, these terminals where a lot cheaper then the competitors. Mind you, cheap still means around $4000, or around $30.000 in 2025 money. But the IBM 2250 was priced at around $280.000 That’s 1970s dollars, so well over 2 million USD today!
Before we move away from these terminals, one last cool tidbit. Tektronix made the 4010 in several sizes, the biggest being the 25″ 4016 with a 4096*3120 pixel resolution. 4K in 1974, sign me up!
The 405x computers
OK I promised computers, so let’s move to the Tek 4051 I got! Released in 1975, this was based on the 4010 series of terminals, but with a Motorola 6800 computer inside. This machine ran, like so many at the time, BASIC, but with extra subroutines for drawing and manipulating vector graphics. 8KB RAM was standard, but up to 32KB RAM could be installed. Extra software was installed via ROM modules in the back, for example to add DSP routines. Data could be saved on tape, and via RS232 and GBIP external devices could be attached!
All in all, a pretty capable machine, especially in 1975. BASIC computers where getting common, but graphics was pretty new. According to Tektronix the 4051 was ideal for researches, analysts and physicians, and this could be yours for the low low price of 6 grand, or around $36.000 in 2025. I could not find sales figures, but it seems that this was a decently successful machine. Tektronix also made the 4052, with a faster CPU, and the 4054, a 19″ 4K resolution behemoth! Tektronix continued making workstations until the 90s but like almost all workstations of the era, x86/Linux eventually took over the entire workstation market.
The 4051 was also used in a few series/movies, the storage CRTs do not flicker when recorded like a normal CRT and as they run basic, getting something cool on screen was fairly easy to do! The best known example was Battlestar Galactica:
Fixing a Tektronix computer
With the history out of the way, what’s the shape of the one I got?
It was stored in a shed for a long while, state unknown, but it looked like it’s in OK shape. A bit dirty but who isn’t at times. Fuse is intact, and when opening it up, nothing looked “off” no bulging caps or such. But turning it on and nothing happens. Anticlimactic…
A good bit of tracing wires later, it turned out the ON/OFF switch is broken. So to quicly remedy this, some wires can be used.
I do NOT recommend this. 230V via cheap breadboard wires is not smart. But with this, still nothing. Argh. So another bit of debugging later it turned out a wire of the mains transformer was not connected to the terminal.
It’s kind of visible in this photo, there are wires going from the transformer to the tabs to select voltages and one was broken. Luckily there was enough wire left to solder on and fix it, getting a replacement would have been impossible! After this fix, I got power! I disconnected as much as I could in order to check all the voltages I could check. We need 15V, 12V, 5V, -12, +20, -20 +185 and +365 and they turned out to all be in spec. Tektronix :)
So, time to slowly connect boards back in and see if something explodes!
Wait I didn’t mean that as a suggestion… Sadly this resistor didn’t understand sarcasm and decided to go up in smoke. It’s a 47 ohm resistor that limits a 320V supply a bit. Perhaps it got a little too warm, or age got the better of it. I did check everything after the resistor and all measured OK. No transistor in a short or capacitor that imploded. So let’s just replace this and pray?
Neat, that worked!
Calibrating that display
Something appeared on the display, which is a BIG improvement, and it all looks like the machine wants to boot. But the display is completely unreadable, which means it’s time to calibrate all voltages.
Which means, measure a power supply that’s almost 4KV. Spicy!
Luckily I have a HV scope probe on loan from a friend! And the HV is in spec. So that’s good, but all the other voltages are not. These CRTs are pretty sensitive to all the needed voltages, sensitive enough that they are calibrated in the factory and the voltages for the exact CRT are written on them:
196V and 75V for this one, and I measured 160V and 55V. yeah that’ll do it! Quite a few calibration steps later the display turned out to be quite nicely readable and in great condition!
The single tape I got with mine is sadly broken. The belt snapped, which seems to be a common issue with these. The drive itself seems to work, and the tape I got is an OS backup tape, so likely nothing too important. This is fixable, but not too high on my to-do list for now.
This turned out to be a less complex repair then expected. Some keyboard switches are a bit crusty, it needs a clean, but a 50 year old computer mostly just working is pretty amazing! So let’s end this repair on a few fun beauty shots of the inside and more:
What did I pick up exactly?
Having a look at my machine, it has maxed out RAM at 32KB, sadly no serial port, but it did came with a ROM Expander!
The back of the 4051 has space for 2 ROM cards. These contain things like extra programs, subroutines for DSP algorithms and more. These can contain 8KB of ROM, and are memory mapped.
If you want more then 2 at any time, the Rom Expander allows you to have 8! Only one is memory mapped at any time, but the OS of the 4051 scans all ROMS on start, and when you run a program on a ROM, it makes sure to send a few commands to the expander to memory map the right one. This is all invisible as an end user and the machine acts like having 8 ROMs, or if you have 2 expanders, 16 ROMs!
I got 3 ROMs with mine, one for an editor program, one to load/store binary data to tape, and one for the optional external floppy drive. Oh, yes, there is a floppy drive! Sadly I don’t have it, but if someone has one collecting dust, do let me know :)
But can it run DOOM?
No
OK any games at all?
How about some monopoly!
Due to the display technique, most games don’t work very well. The display can’t easily be cleared, apart from a full erase of the display. So some games like tic tac toe or monopoly work but anything more active is difficult sadly.
Luckily there are plenty of cool demo’s and programs for the 4051 and it’s bigger siblings. A TON of programs, manuals and more can be found on the Github page from Monty McGraw. There is also an emulator so you can try this all out using any modern computer!
What’s next
One of the projects on Monty’s Github is a GBIP flash emulator. Currently my 4051 has no way to load/store programs, and typing a 1000 line BASIC file is a bit of a pain. So I’m definitely ordering parts for that!
There is also quite a few ROM cards I do not have, so I am working on a ROM board to clone them.
Finally having this beautiful machine up and running is a great step, and I’ll leave it at this for now!
As always, if you enjoyed this blog post, you can buy me a coffee!
So, what do you think ?