Help with waveform on rails - looks unregulated

[mfrimu]

Hello,

While troubleshooting a dead channel on a QED amp I put the scope on the rails and I get what looks like partially rectified waveform, plus 3 phases?

Is my scope broken?
I mean normally the scope works fine. Why 3 phases? Positive end of rectifier bridge shows large sine 1/2 waves. Negative shows smaller ones.

Thnanks.

 

[JoelS]

that kind of look on the scope has to do with the way the triggering is working. there can only be one voltage at any instant of time, but if you believe what the scope is telling you here then there is 3 different voltages at each instant. play with the trigger level, or use more time per division, this should clean up.

is that supposed to be the regulated voltage? maybe the main filter caps after the bridge are not working, or dead regulator

-Joel

 

[willysan]

It's a triggering problem. Try setting the trigger source to LINE.

 

[SoNic_real_one]

Yes the trigger is not working.
In the first pic looks like you have one shorted diode in the power supply bridge.

 

[mfrimu]

Thanks !