# Kempston Joystick Interface Repair

This was part of an Ebay lot. I was actually only interested in the 
zipstick joystick that was part of the bundle, but seeing as the
bundle was less than a zipstick alone. I figured it was worth a 
punt, even though the items were listed as 'untested'.

The interface is an original Kempston Joystick Interface+ in its
original box, complete with the instruction card. Unfortunately on
plugging it in to my spectrum any game I enabled the kepmston
joystick on would steer left and not recognize any other direction,
whether a joystick was plugged in or not. I concluded, after
reading some articles online[1], there was an issue with the logic IC. 
The chip is a DM74LS366AN which no longer seems to be produced. i
Luckily I managed to find one NOS on Ebay for 2.50 GBP including 
postage.

I have removed the logic chip and prepared the board for the 
replacement in anticipation of its arrival. Desoldering the IC with a
good quality solder sucker and cleaning up with solder wick was 
straight forward[2]. 

## Update 17/12/2021
Chip arrived and soldered in. Unfortunately no change in behaviour so
I've ordered a replacement 74LS138N. It's the only other chip on
there so I'm hopeful this one will resolve the issue! 

## Update 23/12/2021
Chip arrived and soldered in. Again, no change so I'm stumped.

One possibility is that, after testing my new game loader which is
fitted with a diagnostics ROM, M1 is reporting as being defective on
my CPU. From what I understand this is fairly common on zx spectrums
and can lead to external devices not functioning or functioning 
incorrectly. It looks like I will be replacing the z80 CPU in the 
near future...

[1](https://oldmachinery.blogspot.com/2014/01/joysticksnstuff.html)
[2](gopher://gopher.icu/I/images/kempston1.jpg)