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Yahoo, success!!! Thank you everyone for helping me out with this, especially DodgyDave who responded so often, I learned a TON and I really appreciate everyone's time and knowledge!
The new MOSFETs arrived today, I swapped them out, applied power and when all the little LEDs on the output side lit up I knew it was a success! 24Vpp and no more DC offset on the low side of the transformer, and 80Vpp on the high side with everything connected. I neglected to check the package size on the diodes I ordered and the new ones are whopper, so they're going in the parts bin for the next project.
Interesting side notes; on the output side the NPN transistors got hotter and hot faster than the PNP. The power supply side didn't get warm at all. I guess they're on/off where as the audio output side are somewhere in-between. I was surprised to see that the amplified output (audio signal) was 180 degrees out of phase from the input. I expected them to be in-phase.
After some more reading about SMPS's, I'm pretty confident that the diode on the high side rectifier went bad first, causing the low side MOSFETs to overload and go bad as well. Apparently this is a common failure mode, though most often caused by a high side capacitor loosing its capacity. I guess a short in the rectifier had a similar effect.
Thanks again to everyone, I really appreciate the help and the learning opportunity! Here are some follow up images:
Audio input/output minimal gain into 2-ohm load:
Transformer low side:
Transformer high side:
The new MOSFETs arrived today, I swapped them out, applied power and when all the little LEDs on the output side lit up I knew it was a success! 24Vpp and no more DC offset on the low side of the transformer, and 80Vpp on the high side with everything connected. I neglected to check the package size on the diodes I ordered and the new ones are whopper, so they're going in the parts bin for the next project.
Interesting side notes; on the output side the NPN transistors got hotter and hot faster than the PNP. The power supply side didn't get warm at all. I guess they're on/off where as the audio output side are somewhere in-between. I was surprised to see that the amplified output (audio signal) was 180 degrees out of phase from the input. I expected them to be in-phase.
After some more reading about SMPS's, I'm pretty confident that the diode on the high side rectifier went bad first, causing the low side MOSFETs to overload and go bad as well. Apparently this is a common failure mode, though most often caused by a high side capacitor loosing its capacity. I guess a short in the rectifier had a similar effect.
Thanks again to everyone, I really appreciate the help and the learning opportunity! Here are some follow up images:
Audio input/output minimal gain into 2-ohm load:
Transformer low side:
Transformer high side:
