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Stubborn kaypro II refuse to work

J

jmellidg

Experienced Member
Joined
Nov 6, 2015
Messages
106
Location
La Coruña, Spain
Hi everybody.

I'm trying to fix a Kaypro II with no success until now.

Motherboard 81-110B1
Character ROM 81-146
Monitor ROM 81-149c

In the very beginning, the Kaypro boot but in the message in the screen there were different letters changed. I posted before in this forum. Trying to fix it, the Kaypro began to show garbage on the screen and the two lights in the disk drives are on.

I was doing a lot of tests with your help during a lot of time. In the meantime, I've changed a 4164 chip that's bad, and a couple more of chips. No way

Just a few days ago, trying to measure the crystals, I realized that the two legs of the 20 MHz crystal was broken. The crystal stay in place because there is a sticker that fix the crystal to the board.

I've taken a crystal from an old card and voila. Again a working kaypro booting from the cpm disk.

I was so happy until I try to write something... It didn't work.

Ok, I've tested the keyboard in other kaypro, and it works flawlessly. Great I was sure that was a problem with the motherboard. Fixed my attention in the baud rate generator, the SIO and the U71 hex inverter. So changed the SIO (I have a spare one), the 74S04N with a 74LS04N, and the baud generator (one at a time) no changes.

The computer boots fine but the keyboard doesn't work. So again with the scope trying to measure the 5 MHz crystal and AGAIN one of the legs is broken again! Same issue and no easy to see because are so close with another chip.

Ok, happy again, tomorrow buy a new crystal and voila!!. I've bought this morning a 5.000 MHz crystal ( no the 5.0068 that I couldn't find) and solder and this is the result.

Computer boots, with message in the screen (the last letter, an A blink) no lights in the disk drives, motor on and no read the system

I try to desolder the crystal and try again, but the same result...

What do you think it's going on??? If I remove the SIO same result

I really appreciate any help, thank you very much for your time!!!
 
Do you get the "normal" boot sign-on message, like:

Code: 
KAYPRO II 64k CP/M vers 2.2

A>

Are you saying that you can't type on the keyboard? or does the DIR command fail to (read the disk and) display the directory?

Note, the crystal you need is 5.0688, not 5.0068. That should be a fairly common baud generator crystal, although I have not tried to get one. On the Kaypro II, that crystal is used to generate the baud for the keyboard, which needs to be 300 baud. I'm not sure how much tolerance there is, and that would also depend on whether the keyboard clock were running fast or slow. RS-232 Async does allow for differences in the baud clocks between both ends, but I'm not sure what the maximum allowed difference is. Obviously, using 5.000 MHz means your 300 baud will be slightly slow. So, if the keyboard were a little fast, you might be exceeding the allowed difference.
 
Hi, I'm afraid that I don't explain very well. This is the message I got before change the crystal. As soon as we change it, the Kaypro doesn't boot into cpm anymore.

The message in the screen that I refered to was the startup screen "kaypro please place your diskette into drive". After the crystal change, the lights in the disk drives are off from the startup and the disk cannot be reading

Now I have a problem with the disk system and I don't know if the keyboard is fixed, but it don't respond to the ctrl-c sequence to reset the system.
 
The 5.0688 MHz crystal is only associated with the baud rate generator for the serial port to the keyboard.

This crystal should not have anything (directly) to do with the disk interface. It could have something to do indirectly if it was not working at all.

The motor on, drive A and drive B select signals are produced from the Z80 PIO at U72 and inverter gates to drive the disk drive.

On a power on situation, the DRIVE A light should illuminate and the motor spin.

It would be worth checking the voltage on U72 pins 8 (motor on), 15 (DRIVE A) and 14 (DRIVE B) after you turn the power on or press the RESET button on the rear.

Pin 8 should be LOW - to turn on the motor.

Pin 15 should be HIGH - to select DRIVE A.

Pin 14 should be LOW - to not select DRIVE B.

If this is the case, we can rule out the Z80 PIO and we need to check the signals further down the line.

Dave
 
Note that at power on, the PIO "outputs" are programmed as inputs, and so both drive A and B LEDs should be on, and motor should be off. This condition normally lasts a few microseconds (maybe a little longer) until the ROM code initializes the PIO. Then later, once the ROM code to attempt a boot is reached, drive A LED will be on and the motor will be on. If the CPU is unable to run the ROM code, of course, things will be different.
 
Hi, thank you guys, I'm long from home until next week, but in fact, the behaviour told by durgadas is exactly it's done before.

I'm afraid that the crystal is irrelevant, at least in my little knowledge, but it's clear that something went wrong in the meanwhile. In fact desolder the crystal and no change..

As long as I return home, I'll test it, thanks for your help
 
The implication is that the MOTOR ON signal has activated but either:

a) The DRIVE A select signal has not activated.
b) The DRIVE A select signal did activate - but the disk drive is either not seeing it, or is faulty.

Dave
 
Everything works until it doesn't!

The only other thing that comes to mind is that you have damaged a PCB track with your desoldering, or splashed some solder where it shouldn't be.

Dave
 
You have a small oscilloscope right? Can you see the serial data coming from the keyboard into the computer? Serial data is really easy to see and decode visually.
 
So, The PIO is OK.

Can you measure the signals after the inverter gates to see what the signals are that are going to the disk drive.

Dave
 
Ok, the inverter was wrong, I changed and the disk system work again. The keyboard still failure. Tomorrow more.. Keyboard with caps light on/off and sound. Thanks!!
 
Hi folks, at least I have my kaypro working!!. The last keyboard fail was a faulty SIO. I'm very grateful to all of you, I'm learning a lot with your help

Thank you very much!!
 
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