4 Nov
2003
4 Nov
'03
9:41 a.m.
Tobias:
Sorry I've fallen behind on the CCtech output, so this is a little behind
schedule.
First, I have schematics of your 2X (also the 2, 4, 10, II, Robie - most
of them except the KII use the same motherboard with different BIOSes and
varying levels of IC population). I can scan them, and send them to you in
a day or three.
Second: your display... unlike terminals where characters arrive serially,
and unlike PCs (and the KII) which have video RAM in the CPU's memory map,
the later Kaypros use a 6845 CRT controller and a custom 40-pin LSI chip.
They form a separate video data/address bus, so any characters incoming have
to be sent to a specified location using registers holding the target video
address. Since the BIOS has to keep on updating the character location to
write to, there's a lot of CPU cycles tied up in the transaction. This is
why the Kaypro video is glacially slow on full-screen updates.
I would suspect that you've got a bad contact on the LSI that bridges the
CPU to the video. Try pulling (gently!) all the 40-pin ICs (6845 and Z80
too) from their sockets, and re-insert them. (Open inputs tend to read as
logic 1, and the worst of your errors occur in the upper screen, where logic
0 is needed for the address.) If enough corrosion built up to mess up the
keyboard, there's a good chance the IC sockets are a little wobbly too. You
might also rub down the IC pins using a pencil eraser if they look
exceptionally cruddy. *Standard ESD precautions apply*
Hope this is useful.
Regards, Bob (and his stable full of orphaned hardware).
Part of original message:
Here are a few more details regarding the problem:
I didn't start my Kaypro 2X for several years. Some weeks ago I gave it
a short try and everything seemed to be okay except for the keyboard.
Due to corrosion many keys didn't react. So I gave it to a friend, who
first tested all the keys to see which were in need to be cleaned. The
display was still okay at that time. Then he opened the keyboard and
cleaned the contacts inside the keyswitches (he had to solder them out
in order to do that). When he had finished the cleaning he assembled and
reconnected the keyboard and started the computer. From that time the
display went silly:
- The powerup message shows up at random coordinates, however some of
the coordinates are okay (see
http://home.arcor.de/toa/tmp/kaypro-defekt.jpg). There are a lot of
additional characters, most of them are '?' (n with ~ above). A few of
the characters are blinking or show up with low intensity. Effect is the
same with or without keyboard connected. Everytime I hit the reset
button I see another random distribution.
- When you type something on the keyboard (at the CP/M prompt) the
characters show up at random coordinates but the blinking cursor moves
in the way one would expect (one step to the right for each character,
3rd position of new line when you hit return). W/o any keyboard input
the display is stable except for the blinking chars.
- When you type in CP/M commands (I still have all the disks) they get
executed but the output characters show up at random coordinates (see
http://home.arcor.de/toa/tmp/kaypro-dir.jpg for an output of "dir").
Has anyone schematics for the Kaypro 2X?
Any hints what to do next?
Tobias
