I found the SHG wouldn't lock properly even though the servo light was green. First I checked the power compared to reference levels. Input IR was fine (~700 mW) but reflected green was very low, < 1 mW. Next I tried checking the mode spectrum but it didn't show anything at all. After flicking the lock switch a few more times I noticed the green power actually dropped when it locked, so based on that I turned the INV switch to NON INV and now it locks as it should (270 mW green). Basically, we have to do some tweaking of the servo because of changing the EOM