Hi there, firstly thanks for the feedback. I'll try to answer most of the questions.
The unit is called a Lester k from electro harmonix. Unfortunately they don't give out schematics.
'Please tell us how it is you are clocking/measuring.' I'm using a very basic oscilloscope (small kit thing and a voltage meter).
As mentioned I replaced the AD converter with a new one, this had no effect on the problem.
Footswitches work (off/on, fast/slow rotary). All potentiometers behave they are flat out (eg 10) So volume is flat out, drive is flat out. When I measure the voltage on the potentiometers they are all working. That is, they adjust a voltage from 0 to 3.3volts. All pots go to the AD converter.
SCLK pin
I could see a pulse looking wave on this pin.
15 DOUT Digital data output
Looked like 3.3v on this pin
DOUT heads to spansion IC (memory)
"When you say "stuck on 10" do you mean that if you test the voltage at the ADC input, you always get a high voltage regardless of pot position?"
I hope I've explained this a little better. The pots are adjusting the voltage, each pot is sent to a different analogue input on the Ad converter. So I guess the analogue side is working.
'CS has to go low or its in standby.' I'm unsure what this means.
Once again thanks for the help.