Various reports of vibrations from the telescope, typically altitude, were reported during the last few months. Always the problem was solved by changing something in the servo control loop, e.g. disconnecting one or the other tachometers, cleaning the said tachos and finally removing the new alt/az amplifiers. It is believed the main cause of the problem was that the new amplifiers had a slightly too high gain with respect to the old ones (1.62 against 1.5). All the new amplifier gains have now been reduced to $\sim$1.47 and are ready to be tested again.

Thomas Augusteijn 2010-02-09