Atari 800XL Keyboard woes amongst others.

[Toby Rieper]

I've got an old Atari 800XL in need of some repairs. When I received the console it would boot up occasionally and sometimes not I got a brown screen more often than not or a yellow one or a garbled image.  The first thing I tested was the power supply but that seemed fine until I tested again and it was pumping out 8volts intermittently so I'm not sure of the keyboard problem is a result of that?

 

Swapped the PSU for a new one and now keys 1,2,3,4,5,6 and I think ESC do not work. I swear they worked before! I've checked continuity of the keys and they certainly register when they are pressed mechanically. I've also swapped the Multiplexors over but no joy. Could replacing the OS chip and CPU help or is it something else? The RAM and ROM tested fine as well as the Pokey chip in the inbuilt test function.

 

 

[TGB1718]

look here:- http://members.casema.nl/hhaydn/howel/logic/burched/b5_800xl_kbd.htm

 

You can see 1,2,3,4,5,6 and ESC are on Pin 2 of the matrix, check the connector to the main board

[Rybags]

Connector or keyboard ribbon would be the logical things to check.

 

Pokey does the keyscan by selecting row/column using 3 output bits each, it seems not logical that only one row would fail as a result of a chip problem, you'd more likely have 2 rows drop out if a line at the chip failed.

[Toby Rieper]

Heya thanks for your replies. I've checked continuity from one the motherboard to the ribbon cable so I guess I'd need to keep one of the keys and trace the line all the way to the multiplexor chip thanks for the schematics. I'll print them out and get the old multimeter out and report back. Odd that it just suddenly happened.

 

[Toby Rieper]

Thank you all. I had to cut off a cm of the ribbon cable and fashion a new connecting part by exposing the copper traces.