A-440 Reference Oscillator Adjustment

1. Connect a frequency counter and AC voltmeter to the HIGH MAIN OUTPUT jack.
2. Turn on the A-440 front panel switch and allow the unit to warm up for 2 minutes.
3. Adjust the A-440 trimpot (located on the lower left corner of the Filter Board) until the frequency counter reads 440Hz ± 1Hz.
4. Verify the output level is -8 ± 2dB on the AC voltmeter.
5. Turn off the A-440 switch.

Source: MINIMOOG — minimoogservicemanual (manual)