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Help? COCO 1 Joystick & keyboard issue

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So, I bought a coco 1 on auction, and it works fine 64K upgraded as well (yes it runs OS/9 L1 V2.1 and Sailor Man just fine. )
More to the point the problem I have is the joysticks did not work at all (joystick calibration program shows no activity (yes tested joysticks on other machine)) 


So I looked into technical Bulletins and found CC:006 that if memory > 32K then C57 & C58 should be changed from 0.01uF to 0.005 uF  to prevent keys F/G and O to not work. (which in my case G /o are not working on keyboard)

and I did the changeover, but the keyboard situation did not change. 
I also found R50 resistor to read 148 ohms instead of 100 Ohms and I replaced that one as well (part of the joystick circuit) 


Tests performed:
I can trip pin 1 and 16 on the main keyboard connector (bypassing the keyboard) and, I get no reaction for expected "O" key, same for "G" oddly enough I can trip pin 1 and 10-11-12-13-14-15 on the connector and I get properly B,C,D,E,F To show on the screen, same goes for pin 2 with 10 through 15, and of course one could suppose 16 was bad, but no, pin 4,5,6,7 and 16 react to give me the W etc.  and since its a matrix type keyboard I am confused.

The only thing I can see on the diagram is pin 1 and pin 2 are also joystick fire button switch 1 and 2 (right and left joysticks) on the 6821 chip on PA0 and PA1,  thus sharing a "line" and is possible to be bad internally. 
I cannot just swap out the 6821 because of a 64K upgrade that wires 6821 and 6822 together right now . I will order another 6821 and double socket it to keep memory mod but able to swap 6821 if it fails again later (if guilty of being bad) 


Looking deeper in what a joystick does, the sw1/sw2 fire button ground pin 4 to pin 3 of the joystick port, this made me lookin into pin of the keyboard connector, as per the diagram for "joysticks"  and I tested at joystick port with power on, pin 3/4 to be grounded and the answer is No.



I have ordered MC6821P replacements but will not be here before next week.
Any other idea how to test the 6821? I cannot type letter "O" so I cannot run any joystick calibration to see if sw1 and sw2 are triggering all the time.


Also when that joystick pins 3/4 grounding happens, then on the motherboard side, the inductors marked L2/L3 are triggered .  My only problem is that L2/L3 of a value of 3.3uH. I just have not figured how to test them yet and if I can actually find replacements for 8479005 inductors as I dont know if they are Coiled, Choke or Toroidal inductors (see picture if you know)






And yes this joystick problem is related to the keyboard issue of those 2 keys becauise if you look at the diagranm below you will see sw1/sw2 are connected to pin 1/2 of the keyboard matrix/6821 connections of line1/2.




Edited by Texas Tandy restorations
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  • 2 months later...

You should be able to get the missing letters to show up looking at the matrix and jumping the correct pins on the keyboard socket with a little jumper wire. So quickly jumping 2 and 16 should make the O show up. 

The only other thing I could think to test would be to see if pins 1 and 2 on the keyboard connector are shorted to ground or together. 


The 2 switches are each separate circuits 

The keyboard missing letters are separate circuits. 

What do all of these non-connected things have in common? The PIA. PIA's do go bad. 

Maybe the PO plugged something funky in to the joystick ports that fried the PIA. 

Edited by CrAlt
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