Sorry for the delay I've been at the Intersolar convention in SF, CA.
I replaced the differential amp transistors and the amplifier did not work. After several power up cycles of the board with a VARIAC I heard a soft poping sound and smoke appeared in the region of Q403/Q412/Q413. I turned off the power (fast wrist method) and checked these components along with the associated diodes and everything checked out okay. I couldn't see any heat markings on any other components (used an eye loop).
I decided it was time to build a light bulb current limiter and I'll use this to retest the board sans Q412/13. I'll get to it this weekend. Thanks Teemuk, Enzo and especially JM Fahey for the help. I will post outcomes soon.
I replaced the differential amp transistors and the amplifier did not work. After several power up cycles of the board with a VARIAC I heard a soft poping sound and smoke appeared in the region of Q403/Q412/Q413. I turned off the power (fast wrist method) and checked these components along with the associated diodes and everything checked out okay. I couldn't see any heat markings on any other components (used an eye loop).
I decided it was time to build a light bulb current limiter and I'll use this to retest the board sans Q412/13. I'll get to it this weekend. Thanks Teemuk, Enzo and especially JM Fahey for the help. I will post outcomes soon.