Sir static. . . . . . .
Do I connect a meter to test these caps, and then test with power on then off so as to make sure I am getting power to the caps?
The two caps are the storage reservoir caps for the negative and positive power supplies and the side by side capacitors are sharing their central, common positive and negative terminals.
The very outermost terminals are being the separate positive and negative supply points which then pass over to the power amp circuitry which is using a pair of transistors for each power output channel.
Take metering , place it in DC mode and above 50VDC scale and put one probe on the shared central +&- buss and the other probe goes to the outermost terminal of one cap and power up the system only a few seconds to see if there is a DC reading.
Look at the side spec of the capacitor and do not expect voltage above that number.
Keep the central probe in the same place and move the other probe over to the opposite caps outer terminal for its voltage reading, which would be of the opposite polarity . . . . at ~ the same voltage value..
If you do not get readings, the switch mode power supply, within your RED oval, is having problems.
Did you find any blown fuses ?
If you test the 4 power transistors, that will be done by ohmmeter mode and in a no applied power condition.
The emitter resistors . . .not transistors . . . . are the 4 white bisque ceramic units.
My PINK star was on one that appeared to have a crack sloping across its top . . . .unless that was just being an "optical collusion".
You told us OPTIMUS, but there are different series over a time period, with the full ID number, we might find a schematic floating around .
73's de Edd
Aside . . . . .
fer der Bluejets meister . . . . . .an 'ole F86, 105 and F16 thunderjockey here.
Emitter resistor further clarified above . . . .just awaiting his inspection.