Hey gang. I have 4 used mac 500s that I'm preping for the season, new bulbs, new capacitors etc... I fired one up to test it and about a minute later it bulbed off , and it gave me a HOT warning. I did some reasearch and found that you can calibrate the temp sensors, so I did that last night ( I think correctly). I re-struck two of them side by side, and monitored the head temp readings (resetting them both first). One mac read about 45 - 47 deg c, whereas the "hot" one was about to reach 70 c, before I lamped it off as a precaution. I watched them both cool, and they evenutally read together about 22 deg. (-25) on the readout. Any thoughts? - the only difference I can see between them is the plastic housing on the hot one, has smaller vents than the other (but it is a factory cowling). The other difference is there is a different board / wiring scheme inside - I'll take a pic of it and post it, I think it's the only one like it (that i have), the rest seem to have a silver box assy in this area as opposed to an exposed board + components.