I'm a student Electronics technician at my local community college. I have lots of old home theater receivers and equipment that are obsolete.
Do you think it would be a good idea to open up one of these old receivers and see all the parts inside as kinda a way to get hands on experience or just to get a good idea of what some electronics circuits really work?
Yes, I am surprised that you have not dived in there already!
I would have done in my earlier learning days.
Any caution to doing this?
What else are you going to do with the stuff? It is redundant and presumably cost you nothing, so if it is completely destroyed, what have you lost? Not much.
What have you gained? See my signature line.
One word on the safety front, beware of the mains voltages.
After you have opened the thing, and before you apply power, look to see where the mains wiring goes, see where it is connected.
Hopefully most live bits should be insulated, but just look to make sure before you poke around in there with power on, and keep your fingers away from the live bits.
Any testing I could do inside with my digital multimeter?
Try following the various supply lines around the circuit board from the power supply to the various (whatever is in there).
Try following the signal circuits.
Something like an oscilloscope would be useful here, but if you dont have such a thing, just follow the tracks to see the signal routing between various components would be useful.
Look at the numbers on the ICs, look for their datasheets on the internet.
Use the datasheet pin-out diagrams to assist in following the power and signal wiring on the board.
Surface mount components can be a bit of a pain, but they are the present and the future.
Go back 20, 30, 40, 50 years, all the old timers were lamenting these tiny transistors compared with valves, integrated circuits compared with discrete transistors, integrated circuits with more and more pins, surface mount compared with through hole components.
You just have to suck it up and get used to it!
Happy tinkering.
JimB