Sansui AU - 919 Thrift Store Find

at lower volumes, the 717 and 919 series when older have a common problem with channel drop out. two main causes are either a dirty volume pot or a cold solder joint on a PCB that acts like an open at low volumes. I would try cleaning the volume pot first.
And as others have suggested, a recap at some point is highly recommended. When these units were made, Sansui used a glue to hold the PCB components in place prior to wave soldering. Over the years, this glue will chemically react with the component leads, and in some cases eat completely through the lead. If you have any cap work done, be sure to clean off all the old glue.
best

I went through and cleaned all the switches. Something I did not do initially. Seems like it's working fine now. Ran it for a few hours last night. And about an hour + on the lowest volume setting.
Man this is an awfully nice sounding unit. Are these modern amps built like this that much better? Especially some of the more expensive, small units. What can you get for $500 that is built, and sounds like this. I have been playing around with audio for few years. You have to spend to much to get something comparable. I will say that most vintage receivers are highly overrated, and not worth the money people are spending on the big ones. The Sansui is a bargain.
Johnss thanks for your response, but did you read the post prior to yours?

Congratulations!You found a treasure.These are great sounding amplifiers.I just picked AU719 in excellent condition and I can't believe how good it is.It has power, clarity,3D sound-stage and very good mid-range.In my opinion it is hard to find something sounding so right even for more than $1000.00 today.

You payed too much.

You paid a reasonable price i say. With some maintenance and repairs, you will have a beast.