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Thread: Dusting off my Processor Technology Sol-20

  1. #1
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    Default Dusting off my Processor Technology Sol-20

    I've had a Sol-20 sitting on the back bench for many years. I purchased it from a roofing chemical company company in the early 1980's. They were upgrading to one of the 'new' Apple systems. Their complaint was that after the unit was on for about 1/2 hour, it would lose it's mind and run wild.
    IMG_1296.jpg
    Here it is, it came with an Omega 3 hard sectored drive system, a Sanyo composite monitor and some software. It has dates on it like manufactured March 1978. Once I got it home and opened up I found that the roofing company had packed the S-100 slots full of memory boards. There were 4 boards filled with the old 2102 memory chips. Well, it didn't take long to figure out they had a heat problem. These boards would warm up the box until there was thermo run away. My first project with this unit was to build a single memory board with all the memory on it, using a 43256 and two 8464 memory chips, 48k of memory. This reduced the heat generated allot and the computer seemed to work very well. My kids learned BASIC on this machine. But then time went on and the Sol was pushed to the back bench. When I retired a dozen or so years ago, I pulled it out and found that the keyboard was not working very well. So, back to the back. Later I found an article that talked about repairing the keyboard. I copied it and promptly forgot about it again. Today, now that the weather is turning cold and outside activities are waning, I pulled the article and re read it. Seems that repairing the capacitive keyboard key is not a difficult job. I purchased a 'space blanket', but was having trouble finding the open cell foam. I thought I'd try a small hole synthetic sponge.
    So, the Sol was moved to the work bench and opened up. Here is the OmegaByte drive box
    IMG_1483a.jpg
    Here is the Sanyo monitor
    IMG_1484a.jpg
    Here is the Sol-20
    IMG_1485a.jpg
    IMG_1486a.jpg
    Here you can see my 'new' memory board
    IMG_1487a.jpg
    IMG_1488a.jpg
    And with the keyboard out.
    IMG_1489a.jpg
    IMG_1491a.jpg
    IMG_1492a.jpg

    So, as I said I want to try and use the sponge for a spring, but am still searching for some open cell foam, Does anyone know of a source for this stuff? Thanks Mike

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  3. #3
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    Quote Originally Posted by Al Kossow View Post
    I've purchased several sets of their foam pads, with good luck in rebuilding TRS-80 keyboards. However, when I used them in my Sol 20, only a couple of keys worked. I ended up using the pads from a Sun Type 4 keyboard, which worked well. I don't know why the TexElec pads didn't work in the Sol, but you may have better luck.

  4. #4
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    Thanks for the advise. I see that the TexElec pads are on back order, so no telling when I would get them. Since I enjoy experimenting with items, I think I'll try making my own first, just to see how different things work. I emailed TexElec and asked how long the back order is. I also have been reading many of the posts here and see that some people have had luck with weather stripping. Maybe tomorrow I can stop at the hardware store and pick up some. Mike

  5. #5

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    Quote Originally Posted by mloewen View Post
    I've purchased several sets of their foam pads, with good luck in rebuilding TRS-80 keyboards. However, when I used them in my Sol 20, only a couple of keys worked. I ended up using the pads from a Sun Type 4 keyboard, which worked well. I don't know why the TexElec pads didn't work in the Sol, but you may have better luck.
    The technical explanation of why some pads do not work in the SOL-20 keyboard is in this article:

    http://worldphaco.com/uploads/HARDWA...OR_THE_SOL.pdf

    The best result is to take the pads from the SUN 4 keyboard, because they result in the capacitance increase at a key press being more than adequate to be reliably detected for all keys.

  6. #6

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    Quote Originally Posted by Mike_Z View Post
    Well, it didn't take long to figure out they had a heat problem. These boards would warm up the box until there was thermo run away.
    There are serious heat dissipation issues in the Sol-20, there are a number of ways to address it.

    Many were fitted with a power transformer euphemistically said to allow for brown out conditions.

    In my Sol , with a line voltage of 94V rms, there is 8v delivered to the backplane (fully loaded with cards). That is suitable as the 7805 regulators on most S-100 cards requre at least 7.5V input. Also, under these conditions the input voltage to the Sol's own 5V discrete design power regulator is around 7.3 V, it has to be as low as 6.3V before ripple voltages appear in the 5V rail from that regulator.This regulator is an LDO design.

    When the sol is powered from 115V the regulator's heat dissipation nearly doubles as the backplane voltage climbs to 9.5 to 10V. Also in the Sol, the cards are stacked horizontally, trapping heat between them.

    1) the first move is to lower the line voltage to your sol, use a variac, = Variable rotary transformer, use a 200W unit at least though the Sol's power consumption is about 60 to 80W. (there have been other methods using a bucking transformer added in the sol, that is messy and not adjustable unlike the variac), so as to get the line voltage down, probably like my unit it will need to be around 94V rms.
    When you have your S-100 cards loaded, adjust the variac to get 8V on the backplane or input to the S100 cards. At this point you would measure about 8.3 to 8.6V directly on the 56,000uF capacitor's terminals due to wiring voltage drops.

    2) fit a cooling fan, see attached photo. To do this you should not modify or damage anything. It can be done simply by adding two hex screw spacers on two screws already there and use thumb nuts to secure it so that you can remove it to remove cards. Make sure it rotates in a direction that assists the direction of air flow across the cards, from the main fan, You do not need to cut any holes in the Sol's top cover for this added fan (as I have seen some people do, spoiling the housing). You need to manufacture/craft an aluminium mounting bracket for it.

    The above moves will solve your heat issues.

    (I'm just about to publish a design on a constant voltage machine I made for my Sol-20, probably later today, I will post it in the S-100 section).

    After you read the article I referenced on the reply on the post above, you likely will conclude the smart move is to get new pads from a Sun 4 Keyboard. By the look of it, you have the type of pad carrier where these click into place with small retainers(some were glued) the Sun 4 pads have the right geometry stiff plastic base to allow this to happen and be properly retained in the carrier.
    Attached Images Attached Images
    Last edited by Hugo Holden; October 31st, 2020 at 05:06 PM.

  7. #7
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    Hugo, some very interesting information. It will take me some time to digest it all. I read somewhere that the Mylar material has a conductive side. I have verified that on my material. The article advocated that the orientation of this conductive side is important, conductive side toward the CB. Did you notice this? I'm using a 7/16" punch to make my disks. The Mylar packaging doesn't mention the materials thickness, but I have measured approx. 0.0012". An interesting side bar here is that although I had thought that all my disk were one layer, some where actually two. The punch seems to cause some of them to attach to each other. The other item is, I'm not sure of the consistency of the thickness across the sheet of Mylar. From reading your article, the Mylar disk is the important consideration. So I figure that I'll have to check each disk prior to using it.

    Yes my keyboard has the clips that grab the clear plastic disk. I only have removed a few so far. I noticed that the glue used between the disk and foam is rather stubborn to remove. A little alcohol softens it up and it comes off. The sponge I selected for the spring pad is not working out well. When I punch them out, they turn into small hamburger buns, the edges are stuck together. I want to try some weather stripping foam next.

    Do you think the TexElec pads may have to thick of a Mylar pad? Maybe that is why they exhibit poor performance? Maybe the conductive side of the Mylar is not consistent?

    I have no source of any SUN 4 keyboards. So I believe, I'll be attempting to amke my own pads. Thanks for the help. Let you know my progress. Mike

  8. #8

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    Quote Originally Posted by Mike_Z View Post
    Hugo, some very interesting information. It will take me some time to digest it all. I read somewhere that the Mylar material has a conductive side. I have verified that on my material. The article advocated that the orientation of this conductive side is important, conductive side toward the CB.
    If you look at the article : http://worldphaco.com/uploads/HARDWA...OR_THE_SOL.pdf

    there is a good description of the SOL's original pads.

    They were not conductive on either side, not the original ones I found in my keyboard at least. I suspect that they started out a a 0.035mm thick sheet conductive on one side, which then on that side had another 0.035mm sheet applied over it, so what they ended up with was a disc that was close to 0.07mm thick, with the conductive layer close to its center, or about 0.035mm from the surface.

    A calculation on the geometry and assuming the dielectric constant was about 3 and an experiment showing that the minimum capacitance increase to reliably be detected is about 10 to 15pF agreed with the measurements on the original sol pads.

    I bought a number of replacement pads from different sources, none of them had the conductive layer in the middle of the film, it was on one side and unfortunately the material being to thick to reliably raise the capacitance enough for all keys. That conductive side is not supposed to touch the pcb as the constant trauma of contact will wear it off (So don't follow that other advice about facing it toward the circuit board if that is what was said). Though if you put it around this way, it will work initially by shorting the pcb tracks together on key closure, changing the mode of operation of the keyboard to a switch type rather than a capacitance type.

    The keyboard will work in a switch type of mode. Any resistance across the connection on the board, less than about 68k I think, is also detected as a key closure, even though the system was not designed for it. I tried some 10mm diameter conductive rubber discs (for calculator and remote controls etc) they worked, but I did not do this as I wanted the keyboard original and the SUN 4 type work perfectly. Also, there is no need to apply any abrasive cloth or paper to the pcb tracks where the keys are, you could clean them with IPA if you wanted, when the pads are correct (like the sun 4 type) it will work fine, or if you can replicate the original pads, but it would be a matter of finding/making the correct metalized film. I had wondered about "unwinding" a polyester or polypropylene axial capacitor to get it.


    Sun4 keyboards are pretty easy to get:

    https://www.ebay.com/itm/320-1018-Su...Cclp%3A2334524
    Last edited by Hugo Holden; November 1st, 2020 at 03:33 PM.

  9. #9

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    ...PS: I bought a Sun 4 keyboard from that same seller, good price I thought, but in my case it cost $60 to post it here ! They are a very well made keyboard actually and I felt a little guilty taking the pads out of it and rendering it useless, but Sol-20 keyboards are much rarer, so that offsets cannibalizing it I guess. Still I can imagine in the distant future someone desperately searching for a working Sun 4 keyboard.

  10. #10
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    Well..... I'm going with making my own. I spent the weekend reforming the capacitors in the power supply. Seemed to work out just fine. After that I load tested the power supply and that also looked good. The +5, +12 and -12 voltages were right on the money. This morning I reconnected the power supply, the monitor and the keyboard CB sans the keys. The unit came on, no smoke was released. I glued one of my Mylar disk to my finger and pressed it on each of the key pads on the CB and the monitor recorded the correct key code for each one. So I'm rather confident that that this keyboard will work once the key pads are restored. Today, I hope to get out to the hardware store and look around for some other types of foam to make the key springs from. Mike

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