QSC 850 help

[Woody]

Yes its aprox little over 70V. Can the rectifier short under load but test ok out of unit. I removed and tested in diode mode with fluke DMM. Should there be any AC voltage coming thru. I put meter in AC mode and it was around 8V AC.

 

[dorke]

Another thing you can do is swap the secondarys like so:

 

[sndscientist]

Yes its aprox little over 70V. Can the rectifier short under load but test ok out of unit. I removed and tested in diode mode with fluke DMM. Should there be any AC voltage coming thru. I put meter in AC mode and it was around 8V AC.

8 vac could be ripple but probably not. The best comparison i can think of right now is a car analogy. If your car has a dead cylinder you can put in neutral which is a no load condition it will run smooth and sound fine. However then the load hits it you can tell its failing. If i would be willing to bet that one diode is shorted. Perhaps a .04v drop both directions. Under no load it will act semi normal.

 

[dorke]

8 vac could be ripple but probably not. The best comparison i can think of right now is a car analogy. If your car has a dead cylinder you can put in neutral which is a no load condition it will run smooth and sound fine. However then the load hits it you can tell its failing. If i would be willing to bet that one diode is shorted. Perhaps a .04v drop both directions. Under no load it will act semi normal.

A shorted diode in a bridge will behave totally differently!

An open diode could cause that problem but woody says there is none.

 

[dorke]

A shorted diode in a bridge will behave totally differently!

I wanted to say:
A shorted diode will blow the fuse instantly !!!