A12 quit working after 6 months

[budger]

My A12 has been working great for 6 months but now has no output. Tried multiple input/output combinations to make sure it wasn't a cabling issue. No obviously burnt components. No components seem hot, including the voltage regulators. I swapped the SC25 with a working A12 and the SC25 seems fine. Checked U1 voltages: pin 3 +18V, pin 5 -18V. What test points should I try next? Thanks.

[tpryan]

My first guess would be a cold solder joint that has finally oxidized to the point of interrupting signal flow. If you have a scope or signal tracer, apply a test signal and check for presence of signal at key points in the circuit. If you don't, try carefully re-flowing all of the solder joints. You should be able to detect the signal on both sides of the input transformer, the op-amp inputs and output, both sides of the output transformer, etc.

[budger]

Much thanks!! It was a cold solder joint. I re-flowed all of the solder joints and it is working again.