Broken phono pre-amp, is op-amp bad?
If +Vin is measuring differently to the working channel then I'd suspect the op-amp because that input should be close to GND i.e. +13.5 above the main negative rail which I assume will be -13.5V wrt ground - there is nothing other than the opamp and R38 to cause this problem - check R38 and if that is OK pull the op-amp.