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DSCN0202
Serial number: 43-001829
Pot date code: 49th week of 1980

This particular unit was purchased through eBay as “not working”. The CA3280 op amp was dead and there were previous attempts to repair other issues. The 7815 voltage regulator had been replaced by an ECG986, the release capacitor C14 @ 10mfd had been replaced by a 100mfd electrolytic and several traces were lifted from the board in the power supply area. I replaced the main filter cap in the power supply and several electros in the audio path. The power supply was converted to accept an external DC supply. I also installed the correct value cap for C14. I powered up the unit before installing the CA3280 and checked the PS voltage and audio path. With the CA3280 removed from the socket the audio path circuit is complete with no gain reduction control. The Sensitivity and Output controls will work but the Attack and Release controls will have no effect. If you think you have a bad 3280 just pull it out and trouble shoot the audio and power without it installed. Schematic for the pedal is here.

A word of warning on replacing the chips on these vintage MXR pedals, the dip sockets may not reflect the correct orientation of pin one on the IC. The u-shaped notch on the sockets are oriented incorrectly. I have seen a few pedals come through for repair where someone had in-correctly inserted the IC based on the socket orientation. In the picture below pin one of the CA3280 should be aligned with pin 9 of the socket.

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