Quote:
Originally Posted by PJL
The motor pass transistor is on the negative rail (pin 3). Externally the voltages look OK to me so getting to the internals would be the next step!
Pin 1 (39.2/?) = +Power, +Motor
Pin 2 (15.3/15) = +Vcontrol
Pin 3 (0.7/0.3) = -Motor
Pin 4 (0/0) = -Power
Pin 5 (10.8,10.4/10.5) = Control
Pin 6 (9/9) = -Vcontrol
Pin 7 (9/9) = Tacho
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The new controller is quite different in design as Pin 4 and Pin 6 are connected together.
Q1 is a regulator. Your circuit is a bit suspect as I would expect the regulated supply to feed pin 7 of the opamp via R125.
Q3/Q4 look like an astable.