Assuming you have the Innova meter you linked, it has a diode test function. I thing you select the ohms setting and push SEL to get there.
This can read three things: First, a "short" or very low resistance should read zero or close and the meter may beep. No rectifier test connection should read short. Second, it can read a voltage - usually around .05 V: this is the "forward voltage drop" of a diode under test, showing the voltage across it when it's conducting current. Third, open circuit: this is what a diode measures when connected "reverse" when it blocks current flow. I do not know what the display for this is but it's the same as for having the test leads unconnected.
So: select diode test. Connect one meter lead to the rectifier ground/negative output wire. Connect the other meter lead to each of the yellow wires one at a time (all wires disconnected from the harness!). They must all read the same: either show a forward voltage or show as open circuit. Which does not matter, just all the same. Then move the meter lead on the ground wire to the red/positive wire. Test all three yellows gain. Same deal, all three must read the same... the readings should be opposite what you had from ground but they really can't be otherwise. One reading open where you expect the forward voltage will reduce charging by about 1/3. One reading short will reduce it a bit more I think. More than one short or with an open reading where it should be the forward voltage and you'll get almost zero output power.
The CB650SC has a different alternator design than the SOHC4 engines, I haven't seen one in person. The field coil seems to be combined with the output coils and the "rotor" is in two pieces. But: the wiring diagram shows it does have a field coil so the SOHC4 750 regulator should work... although yours probably expects a ground control regulator rather than the 750's +12V control regulator. A fairly simple wiring mod can make it work, if so.
One way to test the alternator is to "full power" the field coil with a jumper wire and run the engine, but I don't know exactly how to do that on a DOHC4. Then measure power output (charge current measurement or watching battery voltage rise). If you get zero... well, I don't know.
One super important tip: after measuring current, always immediately swap the leads back to the meter's volts/ohms jacks. It's just too easy to finish measuring amps, then think "I wonder what the voltage is?" and connect the meter... best case is a blown meter fuse (always a hard to find weird size and spec) or the magic smoke comes out of the meter and it's bricked.
