Yes. quality stuff.

Oxidized switches/controls would be the 1st thing I’d look at, but you could have an intermittent component as well. Does the RCH cut out with all input sources?

i’d leave them alone…

I suspect that you really don’t have an issue with the amp. It’s just a normal power up effect. On the other channel it’s C224-C225. You could replace the 2 electrolytic caps, but it’s probably not going to change anything.

If the pins on the STK s are in the open it shouldn’t be too difficult. Heat the pin where it solders onto the PCB…then use a desolder pump or wick to remove solder. Clean away any debris or solder left overs. Remove & install the module. Be careful to make sure pins go thru correctly and don’t bend. Resolder, check for any shorts or unwanted connections…Magnifying glasses or visor would be really helpful, a dental tool can come in handy to check/clean between pins. Good small point soldering iron is needed of course, one meant electronic PCB repairs. Dim bulb tester is a good idea too.

I found the schematic. The STK 461’s are directly coupled to the speakers. It looks like that there is a feed back cap and RC noise filter on the outputs (C124 & C125) Diagram shows 0V DC on the STK output. (Pin 11) It’s possible that you are getting a DC pulse on the output as the power comes up.

Some movement would be normal in a system without speaker protection relay. I 2nd checking for any significant DC voltage on the speakers. Do you have the service manual?

Nice quality stuff…they were pricey “back in the day”

I’d keep it. That’s quality stuff.

Marantz stuff from that era was well made. It looks well cared for too. It may need some work as others have mentioned…