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Sol20 keyboard issue

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    First confirm that this problem does not happen with a different monitor, it might not even be your SOL that is the problem. Next I agree test the caps related to your keyboard circuit using an ESR meter. I would not shot gun replace them though, you can disconnect from their circuit by removing one of the posts' connection and then test with an ESR meter. This is a point of discussion that comes up from time to time, replace ALL the caps or just find the ones that are known-bad. I guess it's up to you and your solder skills.

    This one will work:

    There are cheaper ESR meters, but you don't want to go too cheap.

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      I may have found my problem while trying to solve another. I have the Sol connected to a power bar and use the switch on that to shut it down or turn it on as the switch on my Sol is getting unreliable. Anyway, I accidentally sort of half pressed it causing it to *very* rapdily cycle power which knocked out the Sol entirely and left me with a screen full of junk.

      Anyway, I know I've got some issues with sockets in my machine so I reseated a bunch of chips and while doing so found the plastic part of the socket at U28 (74163) lifted right off the pins! Anyway, I did my best to reseat that and as I did, I noticed on power up I had both the normal prompt again (whew) AND the keyboard was working immediately! I shut down again, reinstalled the spare memory board... powered up.. nothing from the keyboard. Pressed on the 163 carefully but firmly.. voila.. typing starts again!

      Not sure if it's the 163 or some kind of micro-fracture in the PCB. I don't know for sure but I don't recall U28 being involved with the keyboard. Anyway, pressing there seems to get the keyboard working again and it'll stay working for a long time.


        U28 isn't in the keyboard path but it is in the display path, so a problem there might make it appear to be a keyboard issue. See drawing X-18: it's the character clock divider.

        It give me the creeps every time the board flexes! I dread the day a trace fractures. At least we have nice, pliable, leaded solder elsewhere!


          Yeah. I kind of think it might be a trace or something in that same area that does have something to do with the keyboard and it's getting flexed in just the right way as I'm pressing on U28. I should investigate further but I really don't want to take the whole thing apart to get the motherboard out.


            Maybe use the SOLOS command "SET O=1" to change the default output from the video section to the serial port and use a connected PC to display the output. That should show if there's actually a keyboard-input problem or (just) a video-section problem.


              Maybe use the SOLOS command "SET O=1" to change the default output from the video section to the serial port and use a connected PC to display the output. That should show if there's actually a keyboard-input problem or (just) a video-section problem.
              That'd require having a working keyboard to type in initially no?

              Anyway, I don't think I'm on the right track now. Today I fired it up... no keyboard.. pressed in the same place.. no reaction. Nada.

              The way things have been working is, I turn the computer on from cold, I can't type. If I sit there with the Repeat and a letter key pressed down, after about two minutes, it'll start spitting out that letter at random intervals. At first, maybe 5-10 seconds between, then 3 seconds, 5 seconds, 2 seconds, 1 second, slowly getting better until all of a sudden, it's spitting them out at the normal rate, and now i can type normally. And I can keep typing normally until shutdown.

              My guess is something that controls the strobe is not working right.. and for some reason requires time to 'warm up' before it starts to work. I can't quite wrap my head around it because I'm used to ICs either being totally failed or totally working.. not requiring a warm up to start working. I'm thinking maybe transistor? No idea.
              Last edited by falter; August 5, 2018, 01:15 PM.


                Here's a video of how it goes down. It started working a little faster than usual here because it had already been warmed up a bit before I shut it down.


                You can't really see the cursor letters too well as my phone cam got smashed... but you get the idea.


                  I seem to have a small warm-up problem with my Sol keyboard, too. Earlier, I had intermittent keyboard issue which was a broken / corroded trace (near R26) and a cold solder joint on my first repair.

                  Currently, when I power up, all of the keys seem to function fine except for UPPERCASE. After a few minutes, it starts to work---intermittently, then consistently. I was testing it last night and it worked after doing an UPPERCASE-REPEAT reset combination, but this could be coincidence.

                  One striking thing in your video is the screen glitch when a key is pressed. I don't remember seeing that on my machine, but maybe its an artifact of your camera sampling the monitor refresh?


                    Originally posted by falter View Post
                    That'd require having a working keyboard to type in initially no?
                    The point of the exercise is to separate the (suspected) keyboard problem from the (probable) video section problem due to U28 (which has nothing to do with keyboard input). If the problem actually is the keyboard, the "SET O=1" won't work anyway and you'll get nothing at the serial port. Otherwise, any output from typed commands will be sent to the serial port and displayed on the PC/terminal. Seems like it would be worth trying to determine if there really is a keyboard problem or not.

                    (By the way, what pads are in your keyboard? The TexElec 3mm pads are known to be unpredictably unreliable (from our other lengthy thread) and you really need 4.5mm (Sun Type 4 or equivalent) pads for the keyboard to work well.)


                      Ah I see what you're saying. I tried something similar with SET I=1 --- but could not type anything from my PC terminal to the Sol's screen. I really think this is keyboard or keyboard logic related.

                      For now I am using the very first batch Sara produced... with the greyish coloured discs. It's not perfect but it at least works for now.


                        Originally posted by falter View Post
                        Ah I see what you're saying. I tried something similar with SET I=1 --- but could not type anything from my PC terminal to the Sol's screen.
                        But if there's a video section problem (as your U28 woes imply) you wouldn't see anything from the Sol's video output. The "SET O=1" bypasses the video section for output and all output goes to the serial port. (I can't remember if LOCAL should be off, though.)


                          Okay so when the keyboard isn't typing anything onscreen, SET 0=1 does not work either.. nothing comes out on serial.

                          I've determined that the keyboard is working more or less properly - there is a clear strobe pulse on U10 pin 3, the key detection process is working and a valid code is set up.

                          So now I'm trying to follow this to the PCB but am being hampered by the scan quality/handwriting on the schematic. I'm assuming I want to follow J1 pin 3 on the keyboard to wherever that pin goes from J3 on the PCB. I just can't make out where it is appearing. I *think* there is a pin marked 3 going to U78 pin 11, but I've checked that with my probe when the keyboard is working and there's no pulse there as keys are pressed. Anyone know for sure where it goes?


                            NM.. I think I found it. It's pin 12 of U79.

                            When the keyboard is not working, my probe detects it as being in a low state. If I hit repeat as it warms up and hold a key, it slowly shifts between low and high, erratically. I think maybe this chip is my issue.

                            EDIT: or maybe not. I notice it is actually changing states based on which key is pressed. Not pulsing. Back to trying to figure out the schematic.


                              Found it. It's U70 pin 13. I removed, cleaned, and reseated the chip (an 74LS109)... now the keyboard seems to be working on power up no problem.

                              It wasn't too dirty.. I'm thinking these old TI sockets are the root of a lot of the problems with this machine.


                                Originally posted by falter View Post
                                It wasn't too dirty.. I'm thinking these old TI sockets are the root of a lot of the problems with this machine.
                                I've ended up having to completely strip boards and replace all sockets due to TI and other substandard brands. Not fun.
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