CT 677Driver / CT6220 galvo tuning problem with new Mirrors

[shivahoj]

Hello,
has any of you ever retuned CT677 Scanner driver(s) to new mirror(s) ?

Recently I upgraded my RGB show laser from a pair of cheap Chinese noname galvos to better ones from Cambridge Technologies.
I now have a pair of CT677 driver boards attached to CT 6220 Galvos in a standard XY config.
These were in a CO2-Laser before, and the mirrors (clamped to the Shafts) had a Grey-ish mirror coating, with some corrosion marks on the surfaces.

So I chose to replace them with first-Surface Glass mirrors, of roughly the same size like the old ones, but different thickness.
And I knew that I might have to retune the 677 boards to the different angular momentums and resonance freqs of the new mirrors.
Now both mirrors do a high pitched sound, which tells me they are oscillating. Of course I only leave them energized for seconds.

Thus, I fetched the attached Manual and as instructed, I started the retuning process for the first galvo from Step 1 by first removing the notch filter used to dampen the old (now incorrect) resonance frequency. Galvo 2 is disconnected.

That manual states there should be an audible resonance frequency when tuning through the spectrum.
My problem is that there is no resonance, when I tune through the spectrum from ca. 1 kHz to about 12 kHz.
I have a sine oscillator hooked to the driver board, and a 2 channel oscilloscope connected to the Servo(CH1) and Position(CH2) signal, but no resonance is visible.

How do I go on from here?
Without he notch filter, there is no (audible) resonance.
Can I do without dampening the unknown resonance?
Could there be no resonance?

[mixedgas]

Often the resonance is not audible. In fact the resonance in sine wave can be very tiny, I always end up finding it with the scope or a spectrum analyzer. Sound card spectrum analysis programs are out there, and some of them are very good. You'll need to make an AC coupled cable and maybe an attenuator potentiometer.

Second, recheck your board configuration. I prefer to bypass the notch filter with a jumper made from resistor lead. , rather then trying to use the other method. Usually when this lack of resonance happens there is not yet enough loop gain to close the loop.

I need to read the manual before I comment further.

Steve