Harman Kardon 730

[ikarus75]

I recapped a second 730. Everything went fine, but while testing the receiver I noticed two issues:
I get a popping sound from the left channel when switching the Low Cut switch (audible on all sources).

And there's a strange problem with the Mono switch: on Aux 1 and Aux 2 the sound cuts out and only comes through the speakers for fractions of a second. On FM and Phono, everything works fine – sound from both channels.
Any ideas what could cause this?

 

[ikarus75]

Solved. C518 and an adjacent resistor were bridged by excess solder.
Remaining issue: The Aux 1/2 input is only a problem on my test tablet. It's connected via USB-C and an RCA (cinch) cable. Switching to mono causes the issue on the tablet side.