Quote from: gbono on March 28, 2021, 04:44:19 AM
I thought that if the base voltages vary then the collector currents would also vary but the emitter current (total) would stay the same.
That's the way it's supposed to work, but only when the two base Voltages are pretty close, like within +/- 0.2 or 0.3 Volts. When one transistor takes control, the total or "tail" current can change slightly. In this case, tail current comes through R310 and R309.
Quote from: gbono on March 28, 2021, 04:44:19 AM
With 3.6V on the emitters of the dif pair then Q301 would be off and Q302 would be on - correct?
Yes.
Quote from: gbono on March 28, 2021, 04:44:19 AM
How is Q303 biased? Isn't Q301 supplying bias to Q303?
Yes, Q301 controls how Q303 is biased. In the state you describe, Q301 is trying to turn Q303 OFF which SHOULD allow the collector Voltage on Q303 to rise, something is preventing that from happening. The experiment I suggested above was an attempt to find what is not allowing the Collector Voltage of Q303 to rise. (Note: sometimes Enzo misses things in earlier posts when he comes late to the party.) Since the experiment kind of worked, I would conclude that Q303 is leaky or defective.
Quote from: gbono on March 28, 2021, 04:44:19 AM
Still not able to explain why the voltage at C404 isn't at VCC/2?
If the Base Voltage of Q303 is zero, then it's not obeying it's input OR something else is drawing current around it.