My Klyball 600D build

[ronin47]

See "What happens to my C1P upon RESET?" @ viewtopic.php?p=4500#p4500

Are you getting ACIA access after RESET? Um... U14 6850 Pin 9 / U17 'LS139 Pin 12? If so then check for bad low 1K RAM U31/U45 as the screen won't clear if the stack doesn't work. D/C/W/M? display depends on BASIC ROMS.

Good Luck!

Thanks Mark, I will check.

[ronin47]

See "What happens to my C1P upon RESET?" @ viewtopic.php?p=4500#p4500

Are you getting ACIA access after RESET? Um... U14 6850 Pin 9 / U17 'LS139 Pin 12? If so then check for bad low 1K RAM U31/U45 as the screen won't clear if the stack doesn't work. D/C/W/M? display depends on BASIC ROMS.

Good Luck!

In short Mark, I am getting what looks like normal activity on pin 9 of the ACIA. I also had the 2 RAM ICs in the wrong place as both you and John suggested, but it also looks like they were possibly bad (Or at least one was) so I replaced them and now get this:

IMG20240320105529.jpg (4.14 MiB) Viewed 268 times

Now, I'm not out of the woods yet though, the display is very flickery and I had to hold down a key to even get this to photograph.

What next, I'm not sure since it looks like a key is stuck down, but that is just a guess ATM, so more checks to be done.

I can say it recognises me holding a key down, as the screen stops flickering, and that sort of suggests that it isn't a stuck key, and it could easily be something else. Reset also works as I can see a reset signal at pin 40 of the CPU when pressing break.

However I am largely positive since it means the video circuit and CHARGEN are good, as is the video RAM and it looks like the 2 RAM ICs in the system RAM sockets are also good. I have spare RAM ICs so I should still have enough to fill the bank up when it comes to it.

I think it also potentially means that the ROMs are all good in order to get this far.

Pretty pleased with my progress in the last few days

[Mark]

You've made great progress! It looks like you are almost there!

The screen distortion effect is a indication of a stuck key, the screen is constantly redrawing the prompt due to an invalid key selection. You may be able to isolate it to a specific keyboard row by figuring out what additional key press stops the flickering. 2 keys down in the same row will cause the keyboard decoder to stop returning keys. Then if you press a key in a row that doesn't stop the distortion when others did, then it's probably that key (or column).

Code: Select all

OSI keyboard decode table reference
  Columns read from $DF00, Rows selected by writing to $DF00
C2/C4 series has noninverted values (bit set when key pressed)
C1/Superboard has inverted values, bit cleared when key pressed.

     7    6    5    4    3    2    1    0
 -----------------------------------------
 7- 1/!  2/"  3/#  4/$  5/%  6/&  7/'
 6- 8/(  9/)  0/@  :/*  -/=   rub
 5- ./>   L    O    lf   cr
 4-  W    E    R    T    Y    U    I
 3-  S    D    F    G    H    J    K
 2-  X    C    V    B    N    M   ,/<
 1-  Q    A    Z   spc  //?  ;/+   P
 0- rpt  ctl  esc            lsh  rsh  caps

It could be a bad bit on one of the latches or a bad diode, but check for stuck keys first.

Good Luck!

[ronin47]

You've made great progress! It looks like you are almost there!

The screen distortion effect is a indication of a stuck key, the screen is constantly redrawing the prompt due to an invalid key selection. You may be able to isolate it to a specific keyboard row by figuring out what additional key press stops the flickering. 2 keys down in the same row will cause the keyboard decoder to stop returning keys. Then if you press a key in a row that doesn't stop the distortion when others did, then it's probably that key (or column).

Code: Select all

OSI keyboard decode table reference
  Columns read from $DF00, Rows selected by writing to $DF00
C2/C4 series has noninverted values (bit set when key pressed)
C1/Superboard has inverted values, bit cleared when key pressed.

     7    6    5    4    3    2    1    0
 -----------------------------------------
 7- 1/!  2/"  3/#  4/$  5/%  6/&  7/'
 6- 8/(  9/)  0/@  :/*  -/=   rub
 5- ./>   L    O    lf   cr
 4-  W    E    R    T    Y    U    I
 3-  S    D    F    G    H    J    K
 2-  X    C    V    B    N    M   ,/<
 1-  Q    A    Z   spc  //?  ;/+   P
 0- rpt  ctl  esc            lsh  rsh  caps

It could be a bad bit on one of the latches or a bad diode, but check for stuck keys first.

Good Luck!

Thanks for the info Mark, much appreciated. I'm glad I stepped away from it for a bit and came back as it's really helped the progress.

I did think that a stuck key maybe the issue, and had a bit of a weird thing earlier where it did let me get to the 'MEMORY SIZE?' message, but I couldn't hit return, it just gave me a '-'.

Also, when it was flickering, only the 7 key made it stop, and the '-' key took me to the Monitor, which was odd.

Interestingly after removing the separate SHIFT LOCK switch and fitting a new one, the flickering stopped and the screen is now solid, but the keyboard does nothing.

I'm assuming that the separate SHIFT LOCK switch just bridges the centre pin to wither the left or right pin depending on switch position?

I think the fundamentals of the machine, such as ROM, RAM, Video circuit are now all good, and all I have left is a problem with the keyboard, so I need to go and check all the IC soldering for shorts etc, and I should probably check the diodes haven't failed.

[ronin47]

OK, so it looks like my pair of 74LS125's (U4 & U5) are both dead, which might explain why the keyboard wasn't working.

There will be a short intermission whilst I get some more.

[jbtech]

I'm assuming that the separate SHIFT LOCK switch just bridges the centre pin to wither the left or right pin depending on switch position?

No, I thought so too and bought a little SPDT switch to fit the PCB footprint - but the tracks are configured for a SPST switch and the two outer pins need to be connected to hold the shift lock switch on.

So with a SPDT switch shift lock is never on. I just soldered a small link from the centre to RH pin to solve that problem for the SPDT switch. Without that the keyboard didn't work as expected unless the momentary shift lock key was held on.

Regards, John.

[ronin47]

I'm assuming that the separate SHIFT LOCK switch just bridges the centre pin to wither the left or right pin depending on switch position?

No, I thought so too and bought a little SPDT switch to fit the PCB footprint - but the tracks are configured for a SPST switch and the two outer pins need to be connected to hold the shift lock switch on.

So with a SPDT switch shift lock is never on. I just soldered a small link from the centre to RH pin to solve that problem for the SPDT switch. Without that the keyboard didn't work as expected unless the momentary shift lock key was held on.

Regards, John.

Ahh, OK, thanks for that, I'll have to rework that then, probably not helping that I got that wrong too!!!

EDIT - Rework done, just waiting on replacement ICs now.

[ronin47]

Good lord, U20 is dead too, the /RKB signal is pretty much zero. Have swapped in another LS138 and that gives a decent output, but as is typical, I have no spares.

More ordering happening now.

[ronin47]

OK, more progress!!

I have had some spares in the post today and I can get this far:

IMG20240322133627.jpg (3.77 MiB) Viewed 213 times

System stability is not great, but I also have one or more of the LS138's over at U20, U22 & U23 that are bad/marginal. Hopefully when they arrive I will be able to get something sensible out of it, since the free memory looks a bit odd...

I see this as a big thing though as all the keys 'seem' to work even if the system is unstable.

I feel I can see light at the end of the tunnel now.

[ronin47]

OK, so I got the LS138s today and this is the result:

IMG20240325113846.jpg (3.91 MiB) Viewed 198 times

So the amount of memory is correct now, and I have the full 8K installed. It's stable and will run basic programs, though only small at the moment. The keyboard appears to work normally BTW.

I still have this odd video flickering though, like a key is stuck down (Not visible in this picture), and if I remove U5, an LS125 that forms part of the keyboard circuit, the fuzzy video stops. Also, if I hold down certain keys, the flickering stops.

This IC looks after 4 columns on the keyboard, so I first need to make sure there are no solder bridges around the socket, and I need to try and figure out where the issue is at.

On a positive note, I have video, the machine boots to basic and I can see what looks to be a full complement of RAM, so one I figure out this keyboard issue, then I think it'll be a runner. I'll need to figure out a better display than the 5 inch B&W TV I'm using though!