Well, I found the problem!!!!!! With the multimeter on the diode setting, one of the diodes in the rectifier bridge was reading 0.284V in both directions which isn't correct. The other diodes have a reading of 0.84V in one direction and 0V in the other direction.
The bad diode is a 2000V RU1H fast recovery diode. I couldn't find one in stock anywhere, so I just put three 1000V 1N4007 general purpose diodes in series. I also added a 470,000 ohm shunt resistor across each diode to help protect against transients. There are already disc capacitors across each diode in the bridge, so I didn't worry about adding any more.
As an aside, I noticed that there are two diodes in series in one position of the rectifier bridge, so the designers must have figured their diode choice wasn't big enough. They should have doubled up all four diodes right off the bat.
Original RU1H diode that burned out:
New replacement "diode". Three in series = 3000V:
New diodes installed where burned out diode was.
Thanks again to everyone who helped me find the resistor value!
Hi mate, could you post any symptoms that you had initially on the blog please so I can see if we had the same fault.
ReplyDeleteWas this a fix for "no power" My unit is completely dead. Does this mean my problem is on the board with the 4 big capacitors? If you can provide any help? That would be really appreciated.
ReplyDeleteHi, my cut 50 as broken, my machine already has 2 RU1H soldered together on each space on pcb so 8 all together, the first pair are short circuit, should I solder 4 in4007 together to give me 4000v to replace the pair of RU1H
ReplyDeleteThanks paul