One chip getting hot does bother me. Have you measured the voltage rails. If the voltage is gone, it may be shorted. Just swapping it out may not be a good idea unless you know that it wasn't a failed regulator that caused it to short out. Some of the TO-3 type regulators depend on the screws connecting the case to ground. I have seen case that corrosion caused by dissimilar metals has caused the case to float, causing over voltage and damage to the circuit. I don't know that that is the case of a PET ( don't know what they use for regulators ). Voltage checks are always a first. Dwight
