J. Kissel, G. Valdez, R. McCarthy

I grabbed the recently found GS13 578 with the busted locking mechanism (see LHO aLOG 12932) from EX, opened the can, and inspected the locking rod and gear mechanism inside the can. I didn't find any obvious obstructing stuff that would prevent the locking mechanism from functioning -- it just seems as though the main gear controlling the locking pin has ceased. Without further dis-assembly, with which I'm uncomfortable doing, there's no way to assess the problem further.

While I had the can open, I converted 578 from horizontal to vertical configuration -- a much more robust configuration if we don't have a locking mechanism. Unfortunately, during the process, one of the three fragile metal tabs that engage the corresponding vertical spring (already pretty mangled when I got it) broke in the upper-left corner such that the screw-hole is no longer whole. Luckily there was still enough of the tab left, that I could put the tab in place, and tighten down the square nut enough that it held the tab engaging the vertical spring. 

Attachment Captions:
Pg1 - A picture of the corner of the broken tab, showing the vertical spring engaged regardless of the missing chip.
Pg2 - The bottom of the locking mechanism, showing the locking knob gear, and the main locking pin gear. The gears are engaged, and show no signs of damage.
Pg3 - Looking under the proof mass, at the locking pin. Nothing seems to be interfering.
Pg4 - A shot of the top of the instrument, for ID.

After restoring the can, I increased the tension on the vertical springs to bring the proof mass up into the locking containment ring, as the locking mechanism would do. It's *lock* locked, but it's held against the retainer ring. In this configuration it can now withstand a few g's without bouncing around, and there's much less danger to the fragile horizontal flexures (still the stock flexures, as these were installed before the Stanford team innovated better ones). Note, this GS13 also has a LIGO custom pre-amp (D050358) in it, so the Q is a sludgy 5-ish (ref. T0900457), which is also good for robustness.

From here, I suggest one of two courses of action:
(1) Replace the stock horizontal flexures with the rugged Stanford flexures, such that this GS13 doesn't need a locking mechanism any more. We should have at least a set of these at LLO left in the spare stock.
(2) Send the instrument back to GeoTech, and have them repair the instrument. If so, then then can also replace the broken vertical spring tab.

I'd say the likelihood of instrument failure if shipped it it's current condition is pretty high. 
I'd say swap out the flexures, but will discuss with the SEI/PEM/CDS teams. 

For now, the instrument resides in my office, leaving the summary of these eLIGO PEPI Feed-Forward GS13s as
S/N     Config      Current Location
568        V        EX, in change-room, by bench
574        V        CS, In my office
578        ??       EY, on change-room racks
584        ??       EY, on change-room racks