When first powered up it draws 6.5A. After approximately 30 seconds it steadily drops to around 2.3A. Add another minute and there is like an arcing sound coming from the psu fet's / diodes. I bought this as non working. It would make sound, but fades out after a minute. I could try to contact Xtant for service manual or a schematic.
I have the same audio level in all channels until it drops out and no dc offset. I have only 13V on the rail with 14V going in. Sounds to me like the psu fet's starts to oscillate (crackling sound) the pwm controller also get very hot. Checked the fet's for shorts and didn't find any.
For most testing with a scope, you can get by with 2 timebase settings. 2ms for audio and 10us for power supply. When you set it to 10us every time, you will see about 3 cycles on the display and immediately know that the frequency is about right.
Either the timing capacitor or one of the resistors for deadtime or timing could be out of tolerance.
Nice tips there, thanks. I have checked the timing resistors RT - RD and timing cap CT they are all in spec. Based on those values I calculated the frequency to be around 40KHz. I could try to swap the 3525 maybe its internally shorted?