I have run the ALS-500M for over a year now. It generally does a fine job, driven with 30W and an SWR around 1.5:1. Somtimes, it trips...I can hear the relay open...but then it will close again a few seconds later even without unkeying the mic. Sometimes it's a few seconds, sometimes it's five seconds. But it always keys up again without having to cycle the power OFF and back ON. It doesn't do it all the time...it's very intermittent. Per the manual, the load fault kicks in when the RF frequency does not match the band-switch, or when the reflected power exceeds 70 watts. The load fault is only reset by cycling the power OFF and back ON. The thermal fault kicks in when the temperature exceeds a certain level, and automatically resets when the temperature is back to safe levels. So...it seems to me that it must be the thermal fault kicking in. The amp is mounted to the floor of the truck (no space in between), but there is 12" of open space on four sides and above the amp. I do hear the fan kick in and it doesn't run all of the time. The amp chassis is barely warm to the touch, and I don't feel the fan moving excessively hot air. The A/C is generally on so the ambient temperature is around 70 degF. Any ideas? Open the amp up and make sure there's no dust and debris? RF on the keying line (I added a few turns on mix 31)? Bad temperature sensor? 30W is overdriving it (when I first installed the amp, I measured output power with 10-20-30-40-50W in and 30W is in the linear regime)?