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synchrophaser issues?


Mcmuffin07
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MC-130H, initial write up was that the sync wouldn't hold. 5 or 6 minutes and then it would let go like there was no master. we changed the sync, and our new issue is when #2 is selected as a master, all others drop about 2%. when #3 is selected, #2 shoots up 2% but #1+4 sync up good, follow on the droop ck and everything. we changed the sync again, didn't fix it. tried looking into the pulse gen on #2 thinking it was screwed up and found a broken wire. fixed it, ohmed it out and it was good, but the problem remains. haven't really got the downtime to work it since technically it's flyable but i'm thinking about the sync rack and wiring next. any input would be helpful, she's been broke for a few weeks now.

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It could be the master/slave board on the new sync (two being bad in the same way is a stretch), but I'd put my money on bad wiring. Every single time I've seen this issue, it's been wiring. It can be tricky though. The engine conduit might be bad, but disconnecting it from the prop might make it ohm check good since you are moving wiring around within the braided shielding. You either have to check it while it is still connected to the prop (ohm check from the horsecollar), or ohm check it to ground while moving the front connector around to try to get a worn wire to chafe against the wire-braid. Of course, if you just got it from depot or had major wiring repairs, you might have a crossed wire somewhere in the wing. Seen that before too.

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Identical case is experienced, the finding in our case was a messing signal from no.2 pulse generator to the synchrophaser unit, it was due to looseness/momentarily brake of one wire within the pump housing plug (P392B), (the plug carrying the signal of no. 2 pulse generator towards synchrophaser unit).

Notes:

1- The most suspected area is the pulse generator wiring output within no.2 engine, therefore re-check it from P392B towards fire wall J241B bearing on mind that it may not be detected during static (no vibration/no twisting). If confirmed to be good then go toward the next check points routing towards syncrophaser unit.

2- Sometimes just cleaning and re-tightening plugs/terminals will cure the defect.

Edited by tenten
plug code
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  • 1 month later...

Finishing up a ANG deployment. Had a prop sync issue that we had 2 different wiring issues on. First issue was the wire harness on the prop, bad pulse gen wiring within the prop. Also found a bad chassis ground on the prop sync power supply. We have 2 chassis ground wires on our H 2.5 aircraft. Would check them out if this is still an ongoing issue for you.

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Wiring definitely.

One place that I have seen stuff like this happen is at the rack where the wires enter, its in a bad place and lots of stuff gets thrown around pretty close to there, some planes have a wire guard to protect this area but some dont.

One of the more bizarre places I have seen it was wire chafing in the wing root, reason its bizarre is it checked fine over and over again one the ground; inflight the wings lift and there was just enough movement to short the wire's out inflight but on landing the wings drooped and the short went away.

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