Stetsom EX 3000EQ rectifier question

[barber02]

I have a Stetsom EX3000EQ in for repair. It had half of the power supply mosfets shorted with their center legs melted away as well as their gate resistors and half of the output mosfets were shorted.

I repaired the half of the power supply that was shorted and replaced the gate resistors and the driver IC for the power supply.

I replaced the shorted output mosfets and the driver IC for that bank.

I powered the amp up and it boots up and gives me a single flashing red LED. The power supply drive starts up initially and then stops when a fault is detected.

The single blink of the red LED indicates a short in the output section. I’m not finding a short anywhere in the output section.

I pull the single rectifier in this amp and it tests open out of circuit. It is a dual anode and single cathode design. 300 v 20amp (10amps per side)

The rectifier is STTH2003CT

I am wondering what would cause this rectifier to fail open on both sides or am I doing something wrong testing it with my DMM. Black lead on the center leg and red probe on the outer legs. Maybe my DMM doesn’t have enough forward voltage for it to conduct. I also check for continuity and it reads open.

Please advise,

David

 

[barber02]

Just to follow up on this post. I replaced the opened rectifier and the amp booted up fine with no issues and survived a 1 hour stress test without a hiccup.