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Pitchlock question


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Got a bird that will not overspeed to get a good pitchlock check on the #1 engine. Changed the valve housing, read 57 VAC to ground to valve housing connector and all resistance checks were within specs. Synchrophaser and rack was also changed. Even took the cover off the valve housing to observe the s.b. motor. How far is the \"rack\" supposed to go when you hit the switch? It moves some but not all the way to the end.

Also we get no droop on #1 engine with sync on and master reduced to flt idle. Any help would be appreciated.


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With problems like this, I can imagine the synchrophaser test set would help for checking aircraft wiring and valvehousing components at the same time. When you hit the prop governing check switches, the motor won\'t move much at all, so I wouldn\'t worry about that. The mechanical rack has mechanical stops that prevent the motor from getting greedy and taking or putting too much RPM. If the motor does spin all the way, you\'ve got bigger problems. When I troubleshoot pitchlock problems, I have a process.

1. With engines running, advance throttles to maximum power. Once stabilized, hit mech/gov switches

A. If you pitchlock, no defect noted.

B. If it doesn\'t pitchlock, proceed to step 2.

2. With engines running in the flight range, without moving throttles, hit fuel gov. check switches.

A. If RPM increases, check fuel control fuel toppings rpm and/or change pitchlock regulator.

B. If RPM doesn\'t increase, do sync and droop check/throttle anticipation checks

a. If all checks pass, check wiring for fuel gov check switch.

b. If all checks fail, check both synchrophaser circuit breakers for being pushed in, the synchrophaser itself, aircraft wiring, reference winding, speed bias motor

Basically, since you changed the valvehousing, as long as the rpm of the prop doesn\'t increase, it\'s either aircraft wiring or the synchrophaser. If rpm does increase when you hit the switches, it\'s either the pitchlock regulator or the fuel control settings.

I hope this helps.

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Disconnect the prop control C/P from another engine that is known as a good. Set-up everything as if you were doing a pitchlock check (throttles above flight idle, norm gov, synch to off, and no master selected) Get all the voltage readings from each pin (with the fuel gov check switch on and also with it off. Check those numbers vs your bad prop. Also check power to and from fuel governing check switch, mech/norm switch, also synchrophaser disarming in the throttle quadrat. A loose wire from any of those switches will prevent an overspeed when the check switch is hit. Does the prop act like its in mech gov? You said no droop, but how is throttle anticipation?

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Sorry for the delay, been on the road. Not with that bird though. The pitchlock prolem is still there. We found a bad wiring job o the sync rack, still no joy. Re-wired no joy. Still no throttle anticipation, Bad sync check. #1 will not droop. Kind of a mute point now as the #1 compressor bearing failed on turns ad shot the motor. Anyway, thank\'s for all the help. It did help.

P.S. Anyone know where to get a parking brake cable in Turkey?

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