There is an incredibly detailed paper here on AK by Ecluser on bias on the 2270 and I have used it to get bias control by adding small value resistors in R784 and R785 if I remember correctly, bias transistor replacement and or bias potentiometer. Its not usually much beyond that if the output transistors are not leaky etc. If the traces are good and no toasted components I have only had to replace diodes or emitter resistors in extreme circumstances. The emitter resistors (those big white 0.2 ohm jobs) are not really able to be checked statically to determine their functionality in the circuit. I have been at the point of just wanting to buy a working board many times and have always been able to find and repair the culprit(s) .