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Old 10th Jun 2019, 9:37 pm   #56
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
Default Re: Bell and Howell TQII 1652 16mm projector

Quote:
Originally Posted by PJL View Post
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
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.
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