choosing test point and making voltage measurement

[tl01magic]

imaged below is excerpt from marantz sr9200 avr

what is +5vl and +5vd ?

and to measure each, do I just use the ground pin that is in between?

[WattsThat]

They are two different 5 volt points. Elsewhere in the schematic will have matching +5vl and +5vd arrows.  Your partial schematic shows a connection to +5vl in the upper right corner, it connects to CC16, RC43 and the emitter of QC05.

The power supply schematic section (the source of the voltages) will show if they are from the same regulator or perhaps two different regulators. GND is a common reference point. It is shown with the earth symbol so it is probably connected to the metal chassis of the unit. If that is the case (you need to investigate), you can just clip your multimeter black lead to the metal chassis. You can confirm that the GND point is the metal chassis using the resistance function of your meter.

[tl01magic]

Thanks so much!

That was informative for me.

judging by the size of heatsinks used for the regulators and burn discoloration around them, im thinking the issue will be there.

Thank you for the tip to follow those traces back to their source.

just in case is an easy answer / commonly known thing; are voltage regulators tough to substitute? I know things like power output transistors can be, but hoping voltage regulators are easier to source replacements for obsolete ones.

though maybe all for naught, just noticed amp section has a mains hum to it  :'(  and if I understand right those can be nearly impossible to find cause / too many things / components could cause it. Maybe am wrong but think a good start is checking caps that are on grnd. 

[WattsThat]

The typical three terminal regulators are easy to source, the job is even easier if the part markings are industry standard stuff rather than custom manufacturers numbers.

Measure the frequency of the hum, anything that is a multiple of your supply frequency is a sign of failing power supply filter capacitors. A scope is easiest way to troubleshoot as it provides both frequency and amplitude. A DMM would be the next choice if a scope is not available.