plumsolly
Well-known member
I've got a Thorens TD104 here, with a motor that will occasionally speed up to its fastest speed (much faster than 45 rpm). There is a service manual with schematic and circuit descriptions online, and I've tracked the problem down to the motor control section.
I can recreate the problem by shorting T103. The problem is that when this condition is created (either artificially by me or naturally during operation) T103 continues to conduct until you bring the base to ground or do something else that knocks it out of that state - Even cycling the power to the unit will not undo it. In other words, it seems that if T103 conducts for more than a certain period of time, it latches, causing the motor to increase its speed up to its mechanical limits. This would all be fine if it never got "tripped" in this manner, but it was happening during normal operation.
Can anyone offer any insight as to why its latching, and how to prevent it?
Thanks,
Ben
I can recreate the problem by shorting T103. The problem is that when this condition is created (either artificially by me or naturally during operation) T103 continues to conduct until you bring the base to ground or do something else that knocks it out of that state - Even cycling the power to the unit will not undo it. In other words, it seems that if T103 conducts for more than a certain period of time, it latches, causing the motor to increase its speed up to its mechanical limits. This would all be fine if it never got "tripped" in this manner, but it was happening during normal operation.
Can anyone offer any insight as to why its latching, and how to prevent it?
Thanks,
Ben