Are you running in stereo mode - IIRC it is a bridged output, which could explain the inversion. You also run into grounding issues when in bridged stereo model. Best practice is to use a floating load, and connect scope ground to chassis, and look at the manual to find where the signals are. The manual should help....My 2 cents
Bridged mode - the rear channel is inverted, and fed to the front minus terminal.
Floating load means that neither end of the load resistor is connected to ground. Grounding the load in bridged mode causes the rear channel fuse to go or worse.... FWIW it is probably best to trouble shoot the channels in quad (4 channel) mode to make sure they are all good, then go to trouble shooting in bridged mode.
Bridged amplifiers are always a PITA when it comes to testing on a bench setup. When I setup my bench switch box (long ago....) I put in a switch to isolate the ground on the load, but was still hard to keep it all sorted out.
In 4 channel mode, the - terminal should be ground on front and rear speakers.
In 2 channel mode, the - terminal on the front speakers goes to the rear channel amplifier of that channel and should have an inverted version of the front channel. In 2 channel mode there is no ground for the speaker connections. Grounding the - side will blow the fuse (and maybe cause more problems) in 2 channel mode. The manual does not explain very much - I expected a little explanation and trouble shooting info for modes.
In stereo mode, do not hook the - terminal to ground. I would use a ground to the chassis, and then separately test the + and the - terminals as independent channels. (Same signal but inverted on the negative). Both will have signals on them.
You can also test in 2 channel mode by using both channels of the scope for
+ and - terminals for one channel of amp, then invert the second channel and display in sum mode. (or if your scope has a differential mode, that does the same thing.)
In 2 channel mode, the resistance + or the - terminals of the front speakers to chassis should be about the same value to chassis. However, it doesn't mean much as it depends on so many factors.Okay thank you!!!! So the manual doesn’t explain that very well. So if I just hook up a speaker to it then it should be fine (not a nice pair) as that one side of the coil is technically not ground. In two channel should the negative be measuring open to the chassis the? Is it a bad thing that I’m measuring 145ish ohms?
Dan