SOL-20 _Back to Life?

[redjr]

Hello,

I'm new member on this forum. I joined after doing a bit of research on the Sol-20. I found this to be the most 'active' site for the Sol with 9 unique members posting this year on a few related topics. I guess that's not bad for a 40+ yr old computer.

A bit of history.... I built a Sol-20 from a kit circa 1976/77 timeframe - shortly after it was made available. I was active in helping to form a SOLUS club in Denver in the late 70s. After numerous upgrades/mods and additional subsystems to the original machine over the years, I continued to enjoy its usefulness. My first printer was an old ASR-35? I believe. I then went on to an early dot-matrix printer, and later a RS Daisy-wheel printer. Sadly, my Sol gradually got replaced with newer computers coming on the market. In the late 80s it got boxed up and put in storage for more years than I care to admit. But I always insisted on keeping it and I did.

Just recently I was contacted via the web from a gentleman needing some physical measurements of the Sol. I was more than eager to help out. So, after several moves across the country, that box that was so securely taped up got opened! Out came my Sol. Still looking as good as ever. Brought back a lot of great memories and local associations I had made because of it.

Now for the really sad part.... Even though I had kept the Sol, over the years the 2 disk subsystems I had used with it, a North* MDS, and a dual 8" floppy system (not the Helios), got discarded thinking I would never use the Sol again. In retrospect, a bad choice. In addition, all my documentation, notes, user manuals, newsletters and all software got mistakenly thrown out while I was away on a 2 week assignment. This was not apparent until a few months later when I went searching for some of it.

So now.... I have a Sol that's in very, very good shape aside from being 46 yrs old that was packed well, and kept away from extreme heat and humidity over those years. And no peripheral gear to make it work. I knew of one major upgrade I had done where I installed a mod that increased the video output to 24 lines x 80 characters. However, when I opened it up, I noticed a couple other mods I had made and forgotten about. One was a Z80 CPU mod board, and a small pcb under the keyboard. Not sure what that did. I had also added the xformer/bridge rectifier upgrade to help stabilize the mains voltage? I also noticed the 3, S-100 boards I was using; (1) a 64k RAM board, (2) a George Morrow Disk Jockey 2D/B board, and (3) a Micro Complex, Phase Lock II Dual Density Controller board. Can't remember why there were two controller boards, or if I was using both, or not. Oh, the SOLOS module is also a custom one from Micro Complex. It switches from two different address configuration, C000 and It did some special things with the video mod as well as compatibility with the Phase Lock II controller I believe? But my memory of what did what is very sketchy.

Anyway, what to do now....?

I haven't tried powering it up yet. I read in one of the Sol related threads, that after 40 years all Tantalum capacitors should be replaced? Really? I knew of Electrolytics, but not Tantalums. Can someone confirm. With the way the video and Z80 mod boards attach to the motherboard(via header pins on the bottom that insert into IC sockets), that will be an undertaking I'm not sure I'm ready to do. What's the real risk of not replacing the tants?

Furthermore, without a disk subsystem in place and proper boot disk, it's unlikely that anything will show up on a screen, much less boot. Without my old, old notes, I have no frame of reference of what I had to do to boot it up anymore and no equipment to do it with!

Are original North* boot disks for the Sol still available? I do have a single 5.25 disk drive that may be useable that's boxed up with my Slicer. Not sure what brand it was. It was half-height though. But still no disks. From reading here, I would use the VSG dongle?

After unearthing my Sol, I've spent countless hours visiting & logging useful related sites, downloading software, printing out parts of the SOL-20 Systems Manual, other user guides from products I have and newsletters, etc. IOW, trying to prepare myself for getting this ole machine running again. However, it's just one of many projects on my retired plate now.

Any advice, observations, suggestions, tips and tricks, new things to use, to get it back up and running would be appreciated from the active members on vcfed.org. Here are a few inside pics;

Rick

 

[daver2]

Welcome.

Everything SOL-20 related I know about is over here https://www.sol20.org. Manuals, articles, ROM images, programs, etc. etc. etc. Hopefully, you can replace your documentation from here.

As to getting it up and running again, the first thing is to get a notepad and document exactly what you have got. Card placement, switch and link settings etc. etc. etc. Try and build up how the system is currently configured.

Next, take it all apart (or - if you can) disconnect the power supply from the rest of the computer. The last thing you want is to have a faulty power supply regulator kill all of your cards!

Check out the large electrolytic in the power supply and look or signs of bulging or leakage. If you see any, reface the electrolytic capacitors before doing anything else.

Obviously (!) check that the computer is set for the same supply voltage you are going to connect it to. I assume you haven't moved half way around the world though...

Separate the transformer from the regulator board and attempt to power up just the transformer alone. Check the low voltage AC supplies from the transformer with a multimeter set to read AC volts. All we are checking for here is (a) no black smoke, (b) no blown fuses and (c) no burnt out transformer windings (primary or secondary).

If this looks OK then you have a couple of choices with the low voltage (regulator) side.

I generally prefer to remove the electrolytic capacitors from the machine one at a time and reform them. If things look OK, pop them back in and do the same for all of the electrolytics.

I wouldn't bother about replacing any tantalum capacitors at this stage...

Next, power up the low voltage regulators from the transformer and check with your multimeter for the correct DC voltages at the output.

I would put a low-power 12V lamp on the +12V, -12V and +5V outputs to GND just to give the supply a bit of load. Obviously, the lamps connected to the +12V and -12V supplies should glow brightly. The one connected to the +5V supply less so. Make sure that you are not drawing too much current from the +/-12V supplies though. 100 mA at 12V should be good = 1 Watt lamp at most say.

You can measure the DC Volts between the power rail and GND and the AC Volts between the power rail and GND to see how much ripple you have. The less the better! Any significant ripple would probably indicate that the associated electrolytic capacitor is dead.

Once you have a working power supply and no black smoke (!) you can continue.

You need to reduce the system to the absolute minimum and bring it up slowly back to health...

What test equipment do you have incidentally?

If a tantalum capacitor fails open circuit you will never know - you may end up with an unreliable machine. If it goes short circuit across the power rails - you will know about it! You replace any that become little volcanoes!

Dave

 

[daver2]

I suppose the other question is what personality module / ROM(s) do you have?

I assume you have some sort of DISK BOOT ROM - but do you have a copy of something like SOLOS (or one of the other stand-alone monitors) to get it to work in the 'basic' configuration?

EDIT: Ah, I have just seen in your photograph what looks like the Micro Complex Dual Personality Module - so this should probably contain the N* bootstrap and the SOLOS commands (depending upon the setting of the sense switch(es)). This should contain the extended memory test command - which will be useful for testing your RAM out!

Dave

 

[daver2]

I have just reacquainted myself with the SOL-20 manuals.

The assembly / system manual contains procedures for measuring the voltages from the power supply. There are two (2) connectors, one containing +/- 12V and +5V (regulated) and the other containing unregulated DC supplies.

Dave

 

[redjr]

Thanks for your replies Dave.

I'm with you on checking out the basics like the PSU separately first. The PSU is connected to both the mobo and the S-100 backplane via molex connectors, so I can easily test the PSU first and check out the voltages. I did notice the little bucking xformer that was DIY'ed under the keyboard on the PSU side. This was used to reduce the input voltage by about 10% making for a cooler running Sol. It was featured (by Joe Maguire) in one of early SOLUS newsletters in August 1978. From a physical standpoint, other than the age factor of the components, my Sol was well cared for while I was using it, and it was never exposed to the elements in any way during storage. No signs of rust anywhere. So I'm hopeful, I won't experience many (if any) failed components issues on power up and testing. But the PSU will be checked for correct voltages first. I did visually examine the large PSU electrolytic cap, and there are no obvious signs of bulging. But that doesn't necessarily mean it is not faulty or failing due to age. For good measure, I may just replace it if I can find a suitable part. It's a 54,000MFD @15VDC capacitor!
Now for the issues presented in your 2nd paragraph of the your first post. That will be a lot harder without the ability to easily hook backup the peripheral gear I was using at the time I decommissioned it. I know what PCBs are in it, but whether or not they were all being used at the time I don't recall. I can only assume they were. The big important mods I made are clearly visible and obvious as to what they do/did. And, the SOLUS module is the Micro Complex Dual Personality Module switchable one that incorporated code for the North* floppy drives. And, I can only assume I was also using Micro Complex's Phase Lock II controller in conjunction with the personality module and drives. The Z80 mod was also another product from Micro Complex. Like the video mod board, it too was incorporated into the existing Sol mobo using pin headers and jumper wires. I guess I was a big fan of their products. I can certainly review all the dip switch settings on the mobo, and the other boards I had to determine how they were set to function. I think the software angle will be the real challenge, once I get past the basic 'operationality' of the Sol mobo and personality module. I'm not sure what it will default to on boot. However, upon examination 'under the hood', it appears I made a few mods that are less obvious as to what they do. A ribbon cable going to various points, pins lifted from ICs with wire-wrap solder to another point somewhere else. I would have no idea what these did, or what they fixed (or enhanced), without my personal notes. Those really are the key and they're gone, so this will be a very slow process.

Speaking of Micro Complex products... I had the chance to meet the owner of the Micro Complex operation, Bob Hogg of Mission Viejo, CA. I was in CA on business and arranged to pick up the new video mod PCB at his home (he was operating out of his garage at the time). I remember he also programmed an EPROM on the fly that I would need to swap on the personality for the video card to work.

As for replacing documentation. I have already scoured many of the Sol related sites and have started the process of downloading information and software. I've already got some manuals and other documentation for what I have. That includes Jim Battle's excellent Sol20.org site you mentioned. Much has been downloaded from that site alone. I've even downloaded a couple years worth of the SOLUS/Proteus newsletter, because they were an ongoing source of valuable information, software fixes, tips and tricks, and just general useful information needed by a budding enthusiast community. So, the information I've already gathered will be hopefully invaluable in my quest, as I've already started to go through some of the documents. I started with the pdf of the Sol-20 User Manual.

I have a lot more to do, so this thread may start to get more active as others hopefully chime in on my successes (or failures) as I attempt to breath new life into this old computer. Never thought I'd go down this road again.

Rick

 

[redjr]

Just doing some simple checking of costs of replacing electrolytic caps in PSU. $106USD Yicks! Sound about right? Is everyone here using their Sol replaced the lytic caps in the PSU?

 

[daver2]

Only $106 !

I have been slowly refurbishing the power supply regulators in my DEC PDP-11/45 and it would come to hundreds of dollars :-(! Fortunately, so far, I have been able to 'save' every capacitor by reforming them. I have to replace the capacitors in one PSU though because they are leaking...

I see from the photographs that you have made a significant number of changes from 'stock'. Being your machine you will at least have some clue as to what you have done and (if you don't) as you start to get into it - it will come back to you.

If you are happy with the power supply - you can risk it and power up the whole machine in one go and see what happens. However, the problem with this approach, is that anything going wrong could prevent the machine from doing anything. I would remove the S100 cards themselves (if this is possible) but you may (then) have to revert some settings - so this is a bit of a two-edged sword...

Formulate a plan first (on paper) - and then run it past us on VCFED to see if we can identify any problems. However, we will need to know what cards are present and (ideally) what the configuration is (as far as you can determine of course).

Any 'bits of pin bending and wiring' you are unsure of - please post them and I can look at the schematics to see if I can work out what they do...

I did note the Z80 add-on. I can understand that processor !

Dave

 

[Hugo Holden]

The very large sized capacitors like the 54,000uF types are generally still excellent. Also on my Sol, the other electrolytics on the psu board were actually fine and tested normal for capacity and ESR. It really all depends on how much actual running time they have had in the past. I bought a replacement large capacitor, but have never needed it.

It is sensible though, not to abruptly apply the line power after years of disuse, just bring it up over 10 or 20 min on a Variac. If any of the capacitors cannot tolerate that sort of very soft start, they are not fit for use and should be replaced without attempts at reformation, because they are simply not reliable if that happens. I only replace the Tants, if they short out.

Don't make extra work for yourself, because there is enough there already with the IC sockets. The TI brand sockets in the SOL were not wonderful, they grip the pins from side to side rather than across the flat, and they are easily damaged if the IC pin array is not formed to the correct spacing prior to IC insertion. Oxides develop on the sides of the pins and the socket claws due to the effects of dissimilar metals. Most of the time consuming work involves cleaning the oxide off every single IC pin on the surfaces that mate with the socket claws and also cleaning, lubricating and testing every IC socket spring claw for tension using an IC pin on a small wire handle. I have written about this on other threads. It is a very big job, but if you don't do it, you will likely be plagued with intermittent faults. The same sort of IC socket an pin cleanup was required on nearly every S-100 board I have.

Though, looking at your Sol's photos you might not have too many of the TI sockets.

There are some issues though with the SOL's power supply, in that a nylon screw was used on one of the power devices (it stretches and loses force) and by now the thermal conductive paste on the power devices will be dry and powdery, diminishing the thermal contact with the heat sink. So it does pay to disassemble the power supply, use a metal screw with insulation, and renew the paste and mica insulators if they need it (I don't use rubber sil pads but stick to the original mica and thermal compound).

The keyboard will need the pads replaced, they have special properties, the closest match is from the Sun 4 keyboard, so buy one as a donor. Other types of pads have been reported to give erratic results, the technical explanation is here:

https://www.worldphaco.com/uploads/H...OR_THE_SOL.pdf

Other articles I have done up relating to the SOL:

https://www.worldphaco.com/uploads/T...REE_BRAINS.pdf

https://www.worldphaco.com/uploads/P...tyreplica..pdf

https://www.worldphaco.com/uploads/S...Ram_Cards..pdf

https://www.worldphaco.com/uploads/The_SOL-20_tape.pdf

The cassette tape interface might not interest you much if you are going back to disk drives (but its pretty clever). I use the N* double density controller card with a pair of 5.25 disk drives and Mike Douglas's wonderful Virtual sector generator so I can use soft sectored floppies.

My Sol had a diabolical power supply problem, pretty rare I would think. The spade terminals, the ones that plugged onto the main bridge rectifier lugs, these were crimped onto the wires, not soldered, one was crimped mainly onto the plastic insulation, but that was concealed by the insulation over the terminal. The bad connection created rapid power cycling at times that corrupted disk files. I only discovered it because I had installed a small onboard digital volt meter and saw the display drop out briefly, it took me ages to find the source of the poor connection.

 

[redjr]

I was never going to power up the whole machine in one go. That would simply be irresponsible on my part. I do enough about electronics NOT to do that.

Phase 1 - Power up strategy;

(1) I will test the PSU separately, connected only to a 12v light bulb. Letting it run for awhile to see how it behaves, monitoring the voltages. The power supply visually 'looks' healthy, but that doesn't mean it is. But if nothings blows when I turn it on, and the voltages stabilize, I can at least move to step 2.

(2) I'll remove all the S-100 cards and only power up the mobo, and check for magic smoke. I will first visually check all my mods and extraneous wires running about to ensure they're all still connected to their original points. I'm assuming none of them changed in storage. Again, letting it run for a bit. If no strange behavior, power down. If strange behavior, magic smoke anywhere, then I'll troubleshoot that and try and determine what's the issue. Check for proper voltages at S-100 backplane connector. I'm going to be optimistic and go out on a limb here and assume there has been no static chip failure over the years in storage. ICs typically fail in the first <90 days of operation. I know it's been 44 yrs, but I'll take my chances. All of my chips are socketed too.

(3) Add in each card individually and power up. Again if no magic smoke, then I can at least assume (power wise) the board is ok. Do that for each board. Check for any onboard LEDs lite - or not. If all boards pass, add all of them back together in the backplane and power up again. One last check for magic smoke. Let run to stabilize. Check for overheating.

Without a monitor yet, I will not be able to determine if the computer boots up to some form of life. That brings me to my next question.... what is the simplest way to go from an coaxial signal/connector to a modern TV or computer monitor. I have no analog anything around. Can I go directly into a composite input? Once I have a suitable monitor connected I can then determine if it boots up and comes to life on the screen with hopefully something blinking!

Phase 2 - Check Mods and Boards for Operation

(steps TBD)

Phase 3 - Software Identification and Operation

(steps and software tools TBD)

Phase 4 - Hookup Suitable 51/4" Floppy Drive and test

(steps and software tools TBD)

Phase 5 - Try and Determine what OS'es I was running and recreate)

o North* OS
o CP/M ?
o BASIC version
o Simple Apps

You are correct in that, the appearance inside my machine leads me to believe I made a bunch of small mods using wirewrap and lifted IC pins. All of which I have no idea what they did. However, I will assume they are still working, and 'may not' directly influence (in a negative way) getting a base system and OS up and running. Many of these mods came directly from the SOLUS/Proteus newsletters. We didn't have the internet and websites back in the late 70's early 80's. Maybe some will start to come back as I investigate and read.

So, I've mentioned I've printed out a couple binders of the newsletters and starting to go through those in hopes of something jogging my memory as a mod I did and can trace it on my machine. This will be a long and slow process. Sadly, I had a lot of custom software done by other people that I used to enhance my Sol experience. One such man was, Fr Thomas McGahee of the Don Bosco Technical School in Paterson, NJ. Very talented guy and did several little custom screen enhancements and other routines that made a difference. Those I will never get back.

More later....

Rick

 

[redjr]

Thanks Hugo for your insight. I've already read or scanned all the threads with Sol-20 in the title or post here on vcfed. Many from you. I've been educated a bit on what's possible today and a PC to get information to the Sol. I have also ordered Mike's VSG adapter. I've already visited your site and bookmarked it for future reference. Some of the articles have been printed and in a binder already. Thanks! I've also been to deramp.com site. Lots of good information there too. I think my first order of business is to get the PSU out and check everything that's been mentioned and noted. I do have a Variac so will add power gradually when the time comes.

For now, once I get it booted, I will stick to focusing on getting some form of my compatible North* system/DOS and CP/M OS up and running. I have a physical drive, but not sure what state it's in. Also my VDM mod, Z80 mod, Phase Lock II controller and personality module are all from Micro Complex are compatible and support North*. They all worked fine together before my Sol was decommissioned. However, I've only been able to find documentation on the Dual Personality Module, nothing else. But all my software is long gone, or in an undiscovered box in my basement. So much of the basic stuff will have to be recreated from images.

Rick

 

[redjr]

One quick question for members who have disassembled their Sol...

I've only done a cursory look at the PSU, but can you easily remove the PSU sub-assembly cage without dismantling the sides, and removing the mobo? Sadly, the reproduction diagrams in the Sol manual available online (that I've downloaded), are incomplete and it's hard to see exactly how it's done. Can you get to all the screws requiring removal?

 

[redjr]

Does anyone have a full-sized reproduction, or complete diagrams at a smaller size that shows the complete PSU assembly structure and assembly exploded views?

 

[redjr]

One quick question for members who have disassembled their Sol...

..... but can you easily remove the PSU sub-assembly cage without dismantling the sides, ....?

No. The right side panel needs to come off.

 

[daver2]

Your 'plan' looks eminently sensible.

I have a video to VGA/HDMI converter that I generally use.

Do you have an oscilloscope? You can always monitor the video signal with the oscilloscope if you do...

Dave

 

[Hugo Holden]

One of the great things about the SOL, is the ease at which you can transfer files to it on its serial link using the CP/M programs PCPUT and PCGET, or just as .ENT files.

When I got my SOL I had never written any 8080 assembly, only dabbled with the 8088 in my 5155. Also I had no experience with single line text Editors. But, I could write the .ASM programs in Notepad on my XP computer,send these to the SOL and assemble them with the Digital Research's ASM in CP/M.

One of the first SOL programs I wrote was for a Walking Man. Subsequently I put that walking man program into ROM in the SOL "3 Brains" project, along with some other programs that do things like wipe specified sections of memory by writing a selected byte to them and memory test programs. Depending on how reliable your RAM is is pays to have a memory test program on hand.I went away from dynamic Ram in the end, to static Ram, so I could run the Dazzler pcb in the SOL.

With regards to the reliability of IC's in the SOL, generally good, but one hex inverter IC failed in mine in front of my eyes while I was using the computer, one of its used input pins inside the package went spontaneously open circuit. A few of the RAM IC's on the main board had also failed.

https://www.youtube.com/watch?v=Pebj4s1sUU0

One thing that is worth doing if you have the Sol main board out of the cabinet, is to replace all of the original DIP switch modules. They have touching gold plated contacts, that get an insulating film over them which makes them either intermittent or open, of course it doesn't matter if the switch is open, if it is supposed to be closed, it can cause chaos with things like the baud rate selection. They were not sealed to the ingress of vapors, and cannot be cleaned properly by spraying contact cleaner into them.

In my Sol I removed the original switches and fitted low profile machine pin sockets, and in those used high quality low profile sealed Omron types that have a body that looks like an IC. This way if the switches ever fail it is just a matter of plugging in new ones, but the Omron switches are so good, I highly doubt if I will ever have to replace them. I had to do the same thing on all of my PT 16kRA memory boards too.

 

[redjr]

I got to the guts of the PSU today. So, I'm learning how to dismantle my Sol. Once I did a visual inspection of everything - primarily the lytic caps, I decided to power it up on the variac. I had a 12v bulb attached for load. As I somewhat expected, there were no sparks, little volcanos, and better yet no explosions! Ultimately no magic smoke either. I was happy. I took the voltage readings and I have to say, after 44 years the PSU seemed to perform excellently. These were measurements;

+12volts = 11.87V
-12volts = 11.93V
+5volts = 5.02V

Now I know nothing was under stress or continuous load for any extended time. But at least it works, and seems stable. I haven't decided whether or not to just leave well enough alone, or swap out some parts or make any changes/improvement to the PSU. It seems to have aged well with time. I'll know more once I power up the mobo, and monitor the voltages under normal conditions.

I do have to say, my electronics and kit building prowess has improved greatly since the Sol. It was really my first big project using ICs and precise solder techniques back in the 70s. Some of mods look like real hack jobs. But I guess they worked back in the day. I found a couple wires on the mobo that had either broken, or come loose and repaired those. I did notice while taking more pictures, under the Z80 mod PCB, there's a 16-pin IC loose on it's back, dead-bug style with 4 wires coming off pins, attached to various other ICs on the mobo. For now I just left it alone.

Rick

 

[daver2]

If you have a variac you definitely have the right tools for bringing up a linear PSU!

I would just leave it soak with no load / lamp load for an extended period of time. I would leave it where you can see it and do something else (e.g. watch a bit of TV, have a G&T etc.). Soaking will be good for everything.

Dave

 

[redjr]

G&T sounds about right.

 

[Hugo Holden]

. Some of mods look like real hack jobs. But I guess they worked back in the day. I found a couple wires on the mobo that had either broken, or come loose and repaired those. I did notice while taking more pictures, under the Z80 mod PCB, there's a 16-pin IC loose on it's back, dead-bug style with 4 wires coming off pins, attached to various other ICs on the mobo. For now I just left it alone.

Rick

I look back at things I wired up or designed decades ago and think, What the heck did I do there ? These days what I do is document everything as a pdf and make a file for my website, then after a few years go by I can look back and see what I did, it jogs the old memory cells.

 

[boxerbomb]

I do have to say, my electronics and kit building prowess has improved greatly since the Sol. It was really my first big project using ICs and precise solder techniques back in the 70s. Some of mods look like real hack jobs. But I guess they worked back in the day. I found a couple wires on the mobo that had either broken, or come loose and repaired those. I did notice while taking more pictures, under the Z80 mod PCB, there's a 16-pin IC loose on it's back, dead-bug style with 4 wires coming off pins, attached to various other ICs on the mobo. For now I just left it alone.

Rick

I received my Sol-20 with modifications already installed. Unfortunately, either with time, or by not being careful opening the case, wires connecting to a piece of perf-board attached to the case were broken and my computer was stuck in a half-modded state. Luckily, I also received the old owners collection of Proteus News and other microcomputer journals. I was able to use pen and paper, to mark which pins on the board where touched by mods, then after I had the master list I flipped through my documents until I found an article describing the 65k mod that matched exactly and I was able to mod in reverse. Hopefully your computer will run fine without it, although it was not uncommon for some mods to cut traces or bend a pin or two out of the socket, but you would probably be able to see those visually.