Hi guys
Does anyone have a schematic for this? The fault is both protect lights on. I fixed one problem already that was causing the negative rail to both amplifier channels to go to -90V with +45V on the positive rail (It's a class G design)
I now have 45V on both rails +/- but one of the amplifier channels has about 20V DC on all the emitter resistors and it all reads weird because the base of the NPN output transistors is about 8V so they are reverse biased, yet the base of the PNP output transistors reads about 19.3V, so 0.7V less than the emitters so those appear be forward biased but this would then put a negative voltage on the emitter resistors, which is opposite to what I have
Also there is no appreciable voltage drop across any of the emitter resistors so there is no current flowing.
I'm beginning to think the 20V on the output of that channel is coming from somewhere else, not via the output transistors. It could be some fault in the protection detect circuit as that must be connected to (and monitoring) +HT, -HT and the emitter voltage (speaker out) yeah?
Both protect LEDs are still on even though one channel has no DC offset on the output (well a few tens of mV maybe)
The amplifier module is marked 406-TXM20-1712A
See pics and TIA
Rich
Does anyone have a schematic for this? The fault is both protect lights on. I fixed one problem already that was causing the negative rail to both amplifier channels to go to -90V with +45V on the positive rail (It's a class G design)
I now have 45V on both rails +/- but one of the amplifier channels has about 20V DC on all the emitter resistors and it all reads weird because the base of the NPN output transistors is about 8V so they are reverse biased, yet the base of the PNP output transistors reads about 19.3V, so 0.7V less than the emitters so those appear be forward biased but this would then put a negative voltage on the emitter resistors, which is opposite to what I have

Also there is no appreciable voltage drop across any of the emitter resistors so there is no current flowing.
I'm beginning to think the 20V on the output of that channel is coming from somewhere else, not via the output transistors. It could be some fault in the protection detect circuit as that must be connected to (and monitoring) +HT, -HT and the emitter voltage (speaker out) yeah?
Both protect LEDs are still on even though one channel has no DC offset on the output (well a few tens of mV maybe)
The amplifier module is marked 406-TXM20-1712A
See pics and TIA
Rich
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