Guitar Pedal help

[3MZ]

I have this old MXR Phase 90 from the mid '70s, and I can't get it to work. When the pedal is turned off it will pass the signal through (the guitar is clean sounding) but when you turn it on there's a small amount of static and no guitar signal. If anybody here knows how to start trouble shooting this please help

[Bush]

Try opening it up and looking for shorts/burnt fuses etc

[Snow_Cat]

Check the rheostat or potentiometer that the pedal actuates.

Sometimes one end of the track breaks.

[3MZ]

I've checked for shorts, etc. obviously, and replaced the potentiometer and switch... I'm fairly certain there is something up with the board itself. How would I check that without just replacing the parts one by one?

[Snow_Cat]

Figure out the signal path then with an oscilloscope or damn good multimeter look for the component that the signal is not passing through as expected.