Help needed with script MXR Dist +

[Rawk100]

Hi, I'm a noobie and could do with some help please......

I've got an old script logo MXR Distortion + which has stopped working. It passes the signal through when its in bypass but when you switch it on you can't hear anything. I've checked the foot switch and measured the resistance across the pots and they seem ok. I've buzzed the circuit out against a schematic and it all seems connected correctly. I don't know if the opamp has died, I measured the voltages on each pin (to ground) and found 7(+ve)=9v, 6(output)=4.5v, 2(-)=4.45v & 3(+)=4.5v. Can anybody help please?.....thanks

[Govmnt_Lacky]

Op amp voltages look good.

Do you have OR know how to make an audio probe? Google can help you there 

Use the audio probe on the circuit and follow the input until you lose the signal.

Good Luck 

[Rawk100]

Thanks for that, i never thought about using an audio probe. I'm going to make one and see if I can find the fault.

[Bill Mountain]

How old are the pots?

I've had pots stop working on me before.

[Rawk100]

The pots are the originals and are dated as 1977 from the serial numbers. I've just started checking them again and think it could be the gain pot as the resistance seems to be a bit erratic. I'm gonna replace it and see if that fixes it....

[Rawk100]

Well this has got me very confused!.....when the gain pot is at 0 (full anti-clockwise) then the pedal seems to work, when i get to about 9 o'clock on the gain the pedal just cuts out. I've replaced the gain pot with a new 500k log and it still does it....any ideas anyone?

[Rawk100]

I still can't get the pedal to work, it's still cutting out when I turn the gain up above 9 o'clock, can any give me a few ideas on what it could be? Cheers.....

[oskar]

I've replaced the gain pot with a new 500k log and it still does it....any ideas anyone?

You usually substitute the pot for a 100k lin as the original is antilog.

when i get to about 9 o'clock on the gain the pedal just cuts out

Try a small cap parallel with the 1M resistor (~10 - 20p).

[Rawk100]

Thanks for those suggestions, I'll give them a go.....