In testing a suspect VFD, I found the diodes in the 3 phase bridge circuit to be giving different readings. Three(3) would read, what I think is proper, 0.4 V, forward biasing and the other 3 would read 1.04 volts when forward biased. The other 6 diodes in the switching circuit also read properly at .36 volts when forward biased. My mates who replaced this machine said they had noticed the DC bus voltages was higher than normal. WOuld the higher forward bias voltage suggest the diodes are depreciating? Would this also have something to do with the excess DC bus voltage?
Thanks in advance
Thanks in advance