I had a aiwa cx-na888 come in with a strange volume control
problem. It wants to go to max volume and stay there no matter
which way the shaft is turned. I don't have the manual yet.
Its a rotary encoder, not a liner audio pot. Both sides of the encoder
seem to look the same when turning the control while looking at them
on the scope. Anyone seen this before and have any insight?
I soldered up a few suspicious connections, but no change.

I'd guess that the circuit probably runs the quadrature outputs of the
encoder through a circuit to generate either of the following two
sorts of signals:

- separate UP and DOWN pulses, or
- a DIRECTION signal and a CLOCK pulse

and then feeds these into some sort of solid-state potentiometer.

I'd guess that either the quadrature-to-pulse translator is frotzed,
or the solid-state potentiometer chip is bad, or there's a bad trace
between them. The translator might be a separate chip, or might be a
software function implemented in the main microcontroller.

Take a look for a Dallas Semiconductor, Maxim, or Crystal
Semiconductor chip (these are, I think, the commonest solid-state
digital potentiometers) and check out what it expects to see at its
inputs. Work back from there towards the encoder.

--
Dave Platt AE6EO
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