Yes it could be a protection diode? problem is it is too chard to be sure about position and the number is V55. looking at the other components the ones labeled 'V' would suggest diodes? problem is 'V' can also mean 'variable component', those outside of being a resistor or cap. My guess is that he put the supply wires around the wrong way. I want to replace this first before i can apply any power to it.

I also scored a 2M88ON that has problems too, Tant has been replaced on that one already so will need to do some scope work to find the issue.