Hi John,
Welcome to the forum. See pages 43 & 44 of your manual (I can't get the Sony Site to download it) so if you don't have it you can read it here
Sony STR-KS370 Manual
I think your KS370 is set to HDMI Pass Through, which has the receiver sense if the TV goes Off or ON and does likewise. Without the remote, it's tough to maneuver around the settings for this unit to switch that option off. However, you may be able to using the front panel buttons on the right of the KS370. The manual doesn't describe how but most Sony Receivers can do this. You'll just have to follow the manual for the steps and experiment with the front panel buttons until you figure it out.
As a last resort, go to Page 24 to reset the KS370, but you will lose all the surround setup. However, this may reset the HDMI Pass Through to off.
1
Press ?/1 to turn on the
receiver.
2
Hold down ?/1 for a few
seconds until "CLEARED"
appears.
All the settings you have changed or
adjusted are reset to the initial settings.
I hope this is helpful.