A1200 Mouse and Joy ports not working

[coutram]

All,

New here, so sorry if I get things wrong! I have my Amiga 1200 which I purchased in the late 80's, it all works apart from I can't move the mouse or joystick.

Left Click and Fire button works, but nothing else.

Can anyone suggest what the problem could be? Board is a 10.4 version (one with blue mouse port attached with grey ribbon cable)

Any help greatly appreciated! Note I cannot solder for toffee, so hoping it's something simple I can fix.

 

[salaxi54]

It usually comes down to a faulty CIA chip, in which case you'd need some expert to repair it.

 

[coutram]

Thanks for the response. That's what I was fearing!

Anyone know of reliable repairers in Devon, UK? :help:

 

[roy_bates]

your board is a 1 D 4 the revision doesent matter if its a cia.the cia's are all the same on these

im sure someone will be along to help you out.

 

[Bryce]

Hi coutram,

The joystick and mouse signals are all handled differently. Fire 0 and Fire 1 go directly from the port (via and small filter) to the odd 8520 VIA, this is the bit that seems to be working. So the VIA doesn't seem to be your problem. The analogue inputs go directly to Paula, but I doubt you've tested these, so we''ll ignore them for now. All the other inputs are fed into a multiplexer (U34) which combines all the movements into a single multiplexed signal. This is the first part that might be faulty. Pin 13 outputs the multiplexed signal, so you could check whether pulses are appearing on this pin when you move the joystick. No pulses? Then you need to swap U34 (it's a relatively easy part to source). If pulses are detected, then the next place you need to check is pin 20 of LISA, if pulses are appearing here, then it looks like your LISA is faulty. Not good, difficult to get and rather difficult to swap for a beginner at least. However, if everything else is ok with your A1200, thena faulty LISA is unlikely.

Hope this helped you with your diagnosis. If you can't do the repair yourself or find someone locally, then send the board over and I'll see what I can do.

Bryce.

 

[coutram]

Bryce,

Thanks for the excellent help! I assume I can find the pulses using a standard multimeter?

Sorry for the basic questions, but all very new to this!

 

[Bryce]

The pulses wouldn't be easy to see with a multimeter. If you don't have an oscilloscope or logic-analyser you could connect an LED with a 470Ohm resistor in series between the pin and GND. The LED should blink every time you move the joystick.

Bryce.