I have just built a regulated PSU (+/- 15v) for a pre amp. Quasar kit 1216 for the CCT diagram,http://www.quasarelectronics.com/1216.htm. When testing the voltages wrt ground, I initially got +/- 15. But the voltages started to creep up slowly until one of the caps went pop at about 24v . I checked and replaced the 15v zenner's and the damaged cap and checked again. Still the same, but this time I turned it off before the voltage got too high.
I have thoroughly checked the board against the CCT diagram and also checked for cold/dry joints. All the diodes and electrolytic caps are the correct way round and no short CCT's. The CCT uses LM317/337T voltage regulators.
Any ideas? Could one or both of the voltage reg's be faulty?