Skip navigation

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 The 7815 voltage regulator had been replaced by an ECG986, the release capacitor C14 @ 10mfd had been replaced by a 100mfd electrolytic and several traces were lifted from the board in the power supply area.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.




  1. Hi,

    On the schematic we can see a CA3080 chip instead of the CA3280E you’re using.
    Is this a mistake on the schematic or was there two versions of the MXR 143?

    On my own pedal, I have a indeed CA3080 chip which is probably dead, can I safely replace it with a CA3280E ?

    Thanks for your advice !

    • The CA3080 is an 8 pin DIP package or metal can on the older versions. The CA3280 is 16 pin DIP package dual version of an improved 3080. I have never seen a 143 with a 3080 chip but the schematic may reflect an earlier version. All of the 143s I have opened have the 3280 16 pin chip. The CA3280 cannot replace the CA3080 without some modifications. The 3280 is extremely rare so I would use the 3080 which are still available in quantities. It would be interesting to compare the two version to see if there is an audible difference. Most 3080 compressors like the DynaComp use the chip in the signal path. The 143 uses it in a feedback loop to control the gain of an opamp. I believe Morley also used a similar configuration in some of their compressor pedals.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: