The SMU topend was removed from the telescope on Thursday, Feb 19 following an apparent instantaneous failure of the Z-axis drive. An inspection established that a pin securing the drive shaft had broken. This (stainless steel) pin was inserted following the Nov/Dec 2003 repair, although the design calls for one made of carbon steel. A new pin was ordered and is expected to arrive today/tomorrow. Installation of the pin and the repositioning if the SMU is expected tomorrow/Wednesday (Feb 24/25) with a FCO to follow.

20040225
From: Remo Tilanus

I am pleased to announce that the repair of the SMU has been completed and want to thank Vernon and his crew for their excellent efforts in returning the system back to service. The SMU was lifted back in place and tested yesterday and the membrane was put 'up' (or 'down' if you wish) and re-tensioned today.

The exact details will be in the follow-up to the fault report, but apparently a small pin locking the Z-motor shaft to the 'hub' had broken. Vernon found that in part this was caused by the hole being too large (or the pin being too small) allowing play between the shaft and hub. Both the hole and a new pin had to be machined to restore a tight coupling.