I assume this will become a generic problem as they age.
A dropper in the fan supply line is R67 of value 150R, barely 2W size
perhaps 1.5W. On the schematic it is marked as 150R 5W.
The relay dropper R66 of value 150R , same physical size, has good green
middle band. The middle band of R67 is something like grey.
Measures 176R, which means that as it increases resistance with age ,
the protect circuit , monitoring both too low or too high fan
current,will engage and amp will drop out.