The bottle number on which the fault occurs varies, sometimes just a
single one (1, 2 or 3) and sometimes any two, or occasionally all 3 -
or even none!

It only beeps having correctly moved to the next stage and when trying
to pump that particular bottle. Pressing the 'Start" button then
activates the pumping process correctly.

There aren't level sensors in the bottles. You program the amount of
fluid and it performs a simple subtraction process to determine if
future runs are possible.

I seem to remember that a very small bit of fluid is pumped

Whatever is malfunctioning should be something that is common to all
three chemicals.

It sounds to me like the Jobo starts the action, detects something
has gone wrong, and beeps for help. Pushing the start button tells
it to try again and this time things go OK.

Before the Jobo malfunctions can you hear the pump running for
second or two to pump 'the very small bit of fluid'? Or is this
a spurt of the previous chemical that may be dispensed by the valves
actuating.

Is the fluid selection valve a rotary valve or are there valves
for each fluid?

Is there a sensor to detect fluid going through the pump/tubing?

Do you get air bubbles in the tubing?

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
To reply, remove spaces: n o lindan at ix . netcom . com
Fstop timer - http://www.nolindan.com/da/fstop/index.htm