DC Offset Adjustment

This information applies to all 607 Audio equipment containing a DC Offset Adjustment circuit.  This circuit is used to inject a small amount of DC into the operational amplifier to nsure no DC is present on the output of the amp.  This procedure should be done if an op-amp change is made, or verified during routine maintenance.

You will need a multimeter, ideally digital, and a slot screwdriver to perform this adjustment.

STEP 1:

Locate the Test Points labelled Ground and OUTPUT on the PCB next to the opamp.  

STEP 2:

Set your multimeter for millivolts and place the red probe on the OUTPUT and black probe on the ground.  Get a reading, it should be in the tens of millivolts.  It can be positive or negative. 

STEP 3:

Ensure the swtich labelled DC-OFFSET-ADJUST is in the on position.  Change the +/- switch next to it from + to - negative and note the change.   If the number on your multimeter is closer to 0VDC start from this position. 

STEP 4:

Using your slot screw driver begin to rotate the brass screw on the trim potentiometer indicated by a 205.  Continue to adjust this screw until the VDC at the output is reading 0VDC.