Sennheiser MKH40 question

At the moment I am repairing a Sennheiser MKH40 microphone.
There is something not clear in the calibration procedure.
The Sennheiser service manual says:

"Check the voltage between the measuring points A(+) and B(-).
Desired voltage is 0 V.
If the value is not 0 V, rotate the coil core of L1 until the voltage is 0V."

But... in the schematic point A is +36.5 V and point B is +37.5 V, so not exactly what you would call 0 V...
I would expect the voltage on point A to be +37,5 V also, because at the top of D3 the voltage is +42 V, and at the bottom of D4 the voltage is +33V. So the difference is 9 V and IMHO this could mean that the voltage between D3 and D4 could be 33 + (1/2 * 9) = 37.5 V.
Am I missing something, or are the voltages mentioned in the service manual (+36.5 and +37.5 V) correct?

Could it be that the differential voltage would give a different result than the voltage on these points referred to ground?

I guess it's not outside the realms of possibility that the 36.5 vs 37.5 might be a slight typo, indeed.

The strange thing is that the service documentation covers the MKH20...70, and all schematics have different voltages for point 'A' and 'B'.

RuudNL said:

Am I missing something, or are the voltages mentioned in the service manual (+36.5 and +37.5 V) correct?

Click to expand...

It isn't important that the voltages are 36 or 37V, important is that the difference is 0V, so the bridge is balanced.

Yes, I understand that.
But the question remains why the voltages on the circuit diagram are different!
(If the voltage difference between A en B is 0 V, those voltages must be the same. Confusing!)

Point A  is high impedance measuring point so it is, most probably, the cause of the lower reading than expected.

RuudNL said:

But the question remains why the voltages on the circuit diagram are different!
(If the voltage difference between A en B is 0 V, those voltages must be the same. Confusing!)

Click to expand...

Agreed, it's confusing; however, the voltages shown on a schematic are taken in reference to ground, where the meter reacts with the measured node's impedance. Measuring the differential value is the correct method for tuning a ratio detector (same as the AFC indicator in FM radio).

Yes, you are right.
I already decided that the 0 V differential voltage is the most important value.