Small Marshall guitar combo amp makes sound only at certain volume levels. On a scale from 1 to 10 on the volume knob, the guitar amp makes sound only at 3,5 and 10. When volume is set to any other level the amp is completely silent. What could be the problem?
Common enough problem - especially with gear that hasn't been used in a while, or kept in dusty places.
Need to get at the back of the volume pot., not much use spraying from outside, so maybe unscrew the chassis from the cabinet - obviously with it all unplugged!
Use switch cleaner spray, and rotate the knob many times. It will probably sound scratchy but eventually will smooth out. Spray some more to rinse the dust away.
If this doesn't do it, you'll need another volume control, same value and same spindle as the faulty one, as the tracking on the original has gone caput. If you can wield a soldering iron, it's a job you could do.
The most obvious culprit is the volume potentiometer: It may be defective or dirty. Try applying, contact cleaning spray, or another specific product, and whipping the knob back and forth.
Another less obvious reason could be the wrong type of potentiometer installed by a technician (linear instead of logarithmic).