The Most Important Computer You Don't Know About

Today - and I can't believe it - we're taking a look at a Sol-20 in beautiful condition. It's the very first ever home computer with built in keyboard, power supply, and video. Let's see if we can get it working.

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#NeXT #SteveJobs #68K

[cruftist]

I remember when I bought my first microcomputer. The local dealer sold the Apple 1 and the SOL-20. I bought a SOL kit and soldered it together myself. I recently finished restoring everything to working order. We should talk.

[Charlesb]

An interesting fact about the Sol-20 was that one of the key guys behind it, Les Solomon, was the editor of Popular Electronics magazine and one of the key backers of a tape data storage standard known as the “Kansas City Standard”. For those that don’t know, back in the early to mid 1970’s the cheapest way to store data permanently was paper tape (aka punch tape) where data was recorded on the tape as punched holes that could be read back by a paper tape reader but it was prone to jamming, tearing, and others issues, and many early hobbyist computer users wanted a more reliable method for storing data. Sol was one of several who had the idea of storing data on a compact audio cassette in the form of two tones to represent ones and zeros, as replacement for paper tape. One problem was that early hobbyist computers all adopted their own incomparable proprietary methods of storage data (as audio) on cassettes. So he and someone from Byte Magazine got together and arrange a meeting/symposium with other early hobbyist computer companies to devise a standard for data storage on audio cassette which became known as the “Kansas City Standard” due to the symposium taking place in Kansas City. Unfortunately, while some computer manufacturers did adopt this standard, many others did not such Commodore, Apple, Sinclair, Atari, and Amstrad, and went proprietary instead. Part of the problem may have been that this standard wasn’t the most efficient method for storing data on tape (as audio) and thus these other microcomputer companies preferred to develop there own more efficient standard, plus there was the added benefit of locking in their users to each company’s own platform.

[johncoenraads]

Not only have I heard of it, I put one together from a kit purchased at the First Canadian Computer Store, which was exactly that. Went on to hook it up to a 10 rank pipe organ thus turning it into a player organ. Also wrote software, all in 8080 assembler, that let me easily enter the musical score even of complex music I could not play. A Bach toccata fitted nicely in 32 kilobytes of memory. Thanks for stirring up some happy memories. Now I'm building Virtual Pipe Organs using Arduinos. It has been quite a ride.

[CasualSpud]

Clint from LGR would be drooling over the woodwork 👍

[PebblesChan]

FYI The 909090… pattern is caused by the CPU executing a recursive 0xFF RST #38 opcode. This happens when the data bus has pull up resistors and nominated memory is not presenting data on the data bus. What’s happening is the CPU reads a 0xFF opcode causes the CPU to execute the code at %0038 which is also another %FF which gets it to run another %FF opcode. As a part of this process the stack pointer is being decremented by 2 with the return address being %0039 (%0038 + 1) being written. After being run so many times the stack pointer contains the video memory address hence displays the %00 %39 characters. To fix your boot problem check out the POJ (Power on Jump) circuit to ensure that the starting signal sequence is correct along with the first memory access is successful.

[idgamingfederation]

my dad had one of these, I tinkered with it a bit but was rather young in the mid 80's and it was not in the best condition. he used to talk about training on a UNIVAC 9700 when he went into the Navy

[Mike_Neukam]

Check the reset circuit for proper operation, and try manually asserting the reset signal through a resistor to see if that will make it boot properly. Check all the address and data lines with an oscilloscope for any seemingly stuck bits. Also check that you have all of the proper clock signals present and timed correctly. I know that the early Altairs had issues with clock reliability, and the 8080 is a bit finicky when it comes to timing, but I have no experience with the SOL. Having that S100 connector right at the top of the expansion bus should make the issue relatively easy to troubleshoot.

[UsagiElectric]

Painted blue steel and genuine wood? I feel like I've found my long lost brother!
Excellent score fam!

This thing is seriously awesome though. Both a gorgeous machine and surprisingly capable for how early it was. As for the "Local" key, my guess is that that is going to be useful when it's in terminal mode. My ADDS terminals have the same functionality. It essentially allows you to shift the terminal into handling things locally without sending or receiving any serial data. For example, if my screen is particularly full of questionable decisions and I want to clear it before flipping the camera on, I can hit "Ctrl + Local" to pop into local mode, and then hit "Ctrl + Erase" to clear the screen without sending any keycodes, and the "Ctrl + Local" again to get back to regular serial terminal operation.

[xsleep]

Most excellent. Never knew this existed. Wikipedia says Felsenstein shard a garage with someone who was building digital clocks in a fine wood case; hence the amazing walnut on this thing.

[Peter_S_]

There's a really good chance that keyboard auto-repeat mod was the circuit from Don Lancaster's CMOS Cookbook which was one of a handful of hack circuits and the end of each chapter called 'A CMOS Cameo'. It worked by intercepting the keyboard strobe line and adding a low frequency oscillator which started running if the strobe line was active for long enough.

[ypoora]

It's really interesting to see this. It's like a classic S100 computer in every way other than having the CPU, memory and terminal integrated. I suppose like an early motherboard!

[voidstar]

Absolutely these are special, glad it has found you! They showed what a kitted-out Altair could become. The Sol-20 is predated by the Wang 2200, Q1, Sphere-1, Datapoint 2200 (all over $5k new in base form) - but still, the Sol-20 was a huge step towards that idea of an actual affordable personal computer with a bus and is about the earliest can-still-power-it-on microcomputer system one can find. We can find late model Wang and Datapoints, but pre-1975 stuff like Mark-8's and early Wang get substantially harder to find in willing-to-power-on working order (the components to make smaller switching power supplies evolved greatly sometime around '72, iirc).

[shmehfleh]

I used to own a Heathkit H-89 computer that could be considered a spiritual successor to this thing. It sported the ability to act as both a computer and a dumb terminal, and could switch between the two modes by pressing a key on the keyboard. Like that Sol 20, it sported a dedicated repeat key instead of just repeating after a second or two delay. It had a shift lock rather than a caps lock, which was basically a mechanically latching shift key. It also used a bank of DIP switches to set various options, like video mode, cursor behavior, etc. And I'm pretty sure it used the S-100 bus as well. It definitely predated the IBM PC and the ISA bus standard.

[rmcdudmk]

I knew a guy who's dad had an Altair when I was in grade school. These old computers are chunky and funky. Thanks for sharing Action Retro. 👍

[startedtech]

Amazing how simple and integrated this is compared to other S100 computers. I have a DIY home-built S100 system I picked up at an estate sale alongside an IMSAI, I'll have to study electronics a while longer and learn power supplies before I dare do anything with it, in the DIY'd linear PSU it's got five of the soup can capacitors. Not to mention the mystery hand made wire-wrapped expansion cards in it.

[stevejackson]

Not sure if you noticed, and this could be caused by YouTube compression. But when you pulled out the personality module it looked like the first contact point was seriously corroded/scratched. Assuming this is the case and not some video glitch - as the OS is loaded from there might this not be the cause of the dodgy loading?

[grimmpickins]

I came to Action Retro for the retro-Mac shenanigans, I stay for the absolutely deep dives into retro computing. You, sir, are a hero. Thanks.

[chironbramberger]

Thanks for all the great videos!

Okay so if it were me, I’d look at the reset signal. If it’s only turning on and working properly like 10% or 25% of the time, then maybe the reset circuit isn’t working properly. Maybe it’s timing is off and sometimes it happens to reset everything the right amount of time but most of the time it doesn’t. Another thing is that if the power supply isn’t putting out the right voltage, or if it can’t sustain all the current the machine needs all at once when it’s powered up, then that might affect the reset circuit, which is often a 555 based timer circuit. However, overall those chips are very oxidized, so a careful cleaning of all the chips and sockets might be a good ideal regardless. If it is a reset circuit problem, then maybe a flakey socket connection due to oxidation is messing with the period of time the reset circuit is holding the system in reset, and cleaning the connections here would allow the circuits timing to work as intended.

Then again with a system this old the capacitors might be bad and the whole system is electrically super noisy and having new capacitors would help.

Without poking around with an oscilloscope and schematic diagram it’s hard to say. But those are my guesses off the top of my head!

[_P_M_]

I remember the full page ads for these in Byte Magazine, paired with (I think) the Helios II (?). I was just a young kid intercepting my dad's magazines. I was fascinated by this stuff. It just looked like the dawning of the future to me. It is so cool to finally see a real one turned on and running. Absolutely gorgeous case. My Dad ran the data processing center for a local bank and so once in a while he'd take me in to see the IBM mainframe. It was like being on the bridge of the Enterprise. All of the machines were bigger than me.

[JohnSmith-xqpz]

Is that a computer or a Star Trek TOS prop?