Yesterday 21st of October 2020 I checked the BF condition again.
Some conditions and what I did:
- Suspension in NEUTRAL mode.
- Current keystone nominal position 100 um.
- I moved the keystone down using coil-magnet actuation in the test channel.
- I measured BF transfer functions in some positions.
What I found, see the picture:
- When the keystone is at 50 um an oscillation at about 40 mHz appears with a small amplitude.
- As the kestone keeps going down the oscillation increases.
- I measured the BF transfer function three times, and the only healthy one is the one with the keystone above 100 um.
What this suggests:
- The problem doesn't seem to be a hard physical stop. The keystone is always moving.
- I tend to think a cable pulling is producing coupling with another body.