1980 MXR Phase 90 problem

[levick11]

I just recently bought a 1980 MXR Phase 90, block logo with block circuit board. For the first few days, it worked sweet. However, now it has a problem or two. When the the button is depressed the first time, the pedal turns on of course. When it is depressed a second time, if the button is held down, the signal is cut off. In other words, the guitar becomes unamplified. Once I release the button, the signal goes on through and everything's normal again. Is that normal for a pedal? (This is my first pedal). But the real problem now is that sometimes when I go to turn the pedal on, the signal is cut off even after I release the button and this is when I'm trying to turn it on, not off. If I wiggle the button a little, or press the button down slightly, it'll come back on, but usually I have to press it a few times to get it to work. Please, can anybody help with this?

[Robert M. Martinelli]

Hi and welcome to the forum!
My first guess would be that the SPDT foot-switch is the culprit ( after 29 years I think it can rightfully ask for retirement )

I'd try to measure ( with a DMM set to measure continuity ) if the switch works properly ( the "common" or "center" terminal should get in contact with one of the outer lugs, then with the other one when operating the switch ). Chances are one of the contacts is not working properly.

If you have good soldering skills you can get a new one and try to replace it yourself, just take note of the connections before de-soldering the old one and rewire the new one accordingly.

An advisable mod would be to use a DPDT switch instead, to achieve true-bypass operation.

Hope this helps

Best regards

Bob

[52 Bill]

Hi and welcome to the forum!
My first guess would be that the SPDT foot-switch is the culprit ( after 29 years I think it can rightfully ask for retirement )

Bob is right, the switch is probably the cause of the signal drop-out.

Before replacing it, I'd try cleaning it with a quality spray cleaner like De-Oxit. This may be all you need to get it working again.

[Mark Hammer]

Switches can fail to provide electrical continuity for a number of reasons:

1) Dirt and grime impeding connection (already addressed in an earlier post)
2) Physical deformation of the movable contacts inside.
3) Long-term tarnishing of the contact and pivot points inside the switch.
4) Long-term deformation of the actuating mechanism inside.

There is absolutely nothing magical in the original switch that warrants replacing. A new one will set you back $5 or so. Spend it.