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It should be clear that the base of Q520 should not be more than -1 2vdc and Q518 +1 3vdc Q516 is -1.2vdc +1.3vdc. the bias and its turn on is the potential difference of RC components R540 and R538. Q518 also gets its controlled DC via Q526 A t ll d i Q526. Assuming th t th voltage amplifier i working correctly, th th amount of i that the lt lifi is ki tl then the t f g governed voltage delivered at the base of Q520 and Q518 should be within the tolerance to be g (controlled) by Q516. In general practice two possibilities exist in this case case. 1. The base drive voltage coming from Voltage amplifier stage arriving at Q518 and Q520 is to high to be controlled by Q516 and its associated components. 2. Q516 and its associated switching + RC and Voltage divider R-Nets are failing. Q526, C538, D506, R Nets D504, R562, are all part of the Q516 operators service as reference control to the bias. Is the problem 1 or 2 or both?