Hi I have an old fluke 77 which works fine but recently on installing 12v 60w light transformers the 77 wasn't picking up the output voltage on AC or DC settings. I assumed wrongly that the transformers were faulty when I connected the lights they worked ok. I tried the 77 on some other types of similar transformers some it worked some it didn't. The ones it didn't pick up I tried my Fluke T120 which did register the voltage.Any ideas I am at a loss.Thanks Mack.