Thank you for the photos. Sorry it’s taken a few days to get back to you, i’ve been really busy.
I don’t see anything directly in the photos that I think could be the issue, but i do notice that a lot (maybe most) of the solder joints have about twice as much solder on them as they should have. Please try to re-flow the solder joints with a clean tip (without solder on it) to see if you can remove some of the solder from those joints, and to ensure that everything is making a good electrical connection. As an example of what i’m talking about, look at the solder joints of the relay, they look more spherical instead of the “concave conical” shape they should have. In fact, the joints on the relay could be causing this problem.
I couldn’t tell too well because some of the photos aren’t in great focus, but it kind of looks like there are little extraneous pieces of solder around the top of the circuit board. These need to be cleaned up because they will cause shorts. You can use your soldering iron to pick them up.
Can you please double check to see if R28 has close to 0V on it? If so, please re-flow the solder joints on the ISP pins, because R28 is connected to some of those pins, and they could be shorted or something. If that doesn’t work, then remove C17 to see if that makes a difference with the volume. Removing this cap will bypass all the signal muting circuitry, so you can see if that is causing the problem.
-Brach