Issue 1.1 18/07/03 SIMRAD
41
Technical Note
FOR THE ATTENTION OF THE SERVICE MANAGER
NUMBER : PS 156
PRODUCT : Powerpilot AP12R / AP14R
SUBJECT : Clutch Solenoid “Chatter”
DATE : 29 October 2001
Background Information
There have been a small number of reported occurrences of the clutch solenoid
“chattering” where a powerpilot was fitted to vessels with a supply voltage in excess of
14v. An investigation was initiated to seek a solution.
Investigation
The investigation determined that, on a small minority of units, the drive to the clutch
was intermittent when the supply voltage exceeded 14v. In these instances it was
found that Transistor TR7 was not being correctly driven into the OFF condition.
During normal operation the base of TR7 is held ON by Resistor R30 to supply and
OFF by port 3.5 of IC1 going low. However, the worst case voltage out from the port in
the LOW condition is calculated as 1.9v (approx) which is too high to turn off TR7. The
provision of a base pull-down resistor of 10KΩ was found to cure the problem.
Solution
Modify affected units by the addition of a surface mount 10KΩ resistor, Part Number
100190, fitted across TR7 base emitter contacts to ensure that TR7 switches off at the
highest recommended limit of supply voltage 16v. The modification need only be
incorporated in affected units though it will be incorporated in all future production.
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