ELENator

This bird has had this problem come back a few times - not repeat/recur though.

Basically, the props wont sync with No. 3 selected as master. Replaced valve housing, no fix. Repalced synchrophaser, no fix. Shot wires on sync rack - all are good. Shot all pins on all plugs on valve housing, tach gen, and pulse gen, and all are good. The last time this happened we found wires in the wrong spots on the terminal board on the electrical rack (TB1C, I believe). After we fixed that, it op checked good. This was a month or two ago. Now the problem has returned. Engine shop replaced the syncrophaser and now they're telling us the problem has gotten worse - it won't sync at all with either prop selected. Obviously the first thing to do is check and see if it's a bad part out of supply. But in every case we've had this issue, the system tests OK with the sync tester set.

Anyone got any ideas?

This bird has had this problem come back a few times - not repeat/recur though.

Basically, the props wont sync with No. 3 selected as master. Repalced valve housing, no fix. Repalced synchrophaser, no fix. Shot wires on sync rack - all are good. Shot all pins on all plugs on valve housing, tach gen, and pulse gen, and all are good. The last time this happened we found wires in the wrong spots on the terminal board on the electrical rack (TB1C, I believe). After we fixed that, it op checked good. This was a month or two ago. Now the problem has returned. Engine shop replaced the syncrophaser and now they're telling us the problem has gotten worse - it won't sync at all with either prop selected. Obviously the first thing to do is check and see if it's a bad part out of supply. But in every case we've had this issue, the system tests OK with the sync tester set.

Anyone got any ideas?

Compare these drawings you may find your answer! The AVR-869 undervolt relay (in TO) and the AVR-869C sequence relay are linked in FEDLOG because they are the same. AVR-869E sequence relay is different. Maybe thats the issue! Thst is of course I'm reading the pictures right!

THank you VERY much for those images. That might help us get the right phase sequence relay to stop these issues once and for all. It still chatters when you run up the APU with external power.

We fixed the problem. It ended up being an external power issue. We swapped phase sequence relays and everything worked as normal. We were almost positive this would be an RCCR/RCR issue.

If you turn the battery on, with the bus not tied, and then apply external power and turn the switch on, every light and relay in the flight deck start flickering and chattering. The thing is, this happens when you start the APU with external power applied as well. This is on an MC-130W aircraft. (87 model).

We've changed the external power contactor, the RCCR between the battery relay and the isolated DC bus, the battery relay, the DC/battery switch, phase sequence relay, a few diodes that checked bad, AC interlock relay, and checked all other diodes and fuses. THe funniest thing happened when we swapped phase sequence relays between two aircraft. One relay was an older, discontinued model while the other was a newer model from supply. The plane works fine using the older relay but freaks out with the newer. We haven't been able to find a reason why this is.

We're on 12s until this is fixed and everyone in our shop is completely flabbergasted. Anyone have any ideas or previous experience?

Would love to talk about it, but have been sworn...

I'm with you on that... I just got back from assisting that entire gig. Man, it's amazing.