"BRASTO" wrote in message
ups.com...
This LENCO MC-4000 stereo receiver when powered on will read Volume
position 16, when rotating the volume control CCW the output volume
increases rather than decreasing. It will stop at MAX 40 and cannot be
reduced. Pulling the powercord for at least one hour will reset the
initial VOL to 16 and the problem can be duplicated at will.

I have inspected the VOL control, which appears to be a sort of
digital shaft encoder rather than the old days potentiometer.
Presumably something is wrong with the logics in the set, can anybody
help to find the cause of the problem or knows its schematics ?

TY
Brasto


This is a *very* common problem on hifi's using a rotary encoder for control
of volume. It is caused by the grease that is put in the shaft bearing to
give it that "stirring treacle" feel, migrating down into the control body,
and contaminating the encoder disc and its pickup fingers.

It is usually a straightforward job to remove the control (two metal tabs
and three pins), bend open the four metal tangs that hold the control
closed, and clean it out. If you use electronics grade isopropyl alcohol on
a cotton tip to deal with the contact fingers, it will usually cause the
grease to 'ball', which makes it easy to remove from them with tweezers or a
pin. Take care with the contacts, as they are quite delicate.The encoder
disc can be cleaned with a cotton tip and alcohol too.

When it's all clean, //slightly// re-bend the fingers to restore their
original contact pressure, put a small amount of switch cleaner / lubricant
on the disc, and reassemble. When refitted to the hifi, you should then have
a working control again. I do probably a couple a month.

Arfa