Picture showing PTC, zener and cut away areas.
I think the green component that I circled in blue looks to be a varistor (MOV). If I'm correct, it is this component that is helping the DM-301 survive your tests.
Yes, I believe it is as well. I had traced out some of the board and the opposite side is the input for the voltage and resistance. There is a string of resistors that make of the attenuator for the different ranges. These are next to the PTC and zener. However, the current input also goes through another attenuator, these are the resistors located next to the MOV. I suspect the MOV clamps anything from the current input only but I did not care enough to dig into it that deep.
I had seen Dave's video with the hi-pot tester where he showed a switch arcing. These sort of videos really don't tell me what I want to know or do anything for me.
For example, say a meter had a MOV right across it's input with say a 600V clamp. You set the hi-pot to 5 KV and no problems are found. The hi-pot can't supply enough current to do any damage and the MOV just is happy to do it's job and clamp it. If you did not know any better you may watch that and think, hey that meter looks pretty good. Its taking 5KV.
I hit the same MOV with a 2KV surge and we find out is was not rated for that energy and BLAM. I want to know if these meters can take the level of energy that they claim they can or not.
I would have liked to have seen Dave surge test each meter he has reviewed to the point of failure and record this. That to me is far more useful data than dropping it off a bridge to see the LCD crack.