ELENator Posted March 24, 2010 Share Posted March 24, 2010 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? Quote Link to comment Share on other sites More sharing options...
Dave in WV Posted March 24, 2010 Share Posted March 24, 2010 I'd call Warner Robins and put them on it. It would seem there's an unexpected problem with the newer part. Quote Link to comment Share on other sites More sharing options...
Herkpilot Posted March 25, 2010 Share Posted March 25, 2010 I hope you find an answer... 9286 has some serious electrical gremlins. Quote Link to comment Share on other sites More sharing options...
bischoffm Posted March 25, 2010 Share Posted March 25, 2010 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! Quote Link to comment Share on other sites More sharing options...
ELENator Posted March 25, 2010 Author Share Posted March 25, 2010 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. Quote Link to comment Share on other sites More sharing options...
ELENator Posted March 25, 2010 Author Share Posted March 25, 2010 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. Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted March 25, 2010 Share Posted March 25, 2010 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). Guess I’m wondering why you apply ext power in this order... If you do not tie the DC bus as soon as you turn on the ext power you apply good voltage... the TR's load the ext power unit until the voltage drops the phase sequence relay senses the reduced voltage and would cycle as the voltage increases and decreases. Sounds like the relay was working just more sensitive.. If you look at the drawings provided notice the diferences in voltages.. Noraml 80-95 vice 100 and dropout voltage 20 vice 5 volts.... Quote Link to comment Share on other sites More sharing options...
Guest Posted April 2, 2010 Share Posted April 2, 2010 We had a similar problem with our '63 year E models. When you tried to apply external power, the switch would chatter/rattle; don't remember that it mattered if the battery was on, tied or off. One of the elect techs opened up an old style Phase Sequence Relay and adjusted the contacts closer and got it to work. We also had problems with the power units causing the switch to chatter and got it to duplicate on our other aircraft even though we had not had a problem previously. Warner-Robins was in the loop, and offered some advice that didn't solve the problem. They were helpful in locating some old style switches. The main contributor seems to be the design of the new sequence switch being too sensitive to otherwise tolerable power fluxes. Quote Link to comment Share on other sites More sharing options...
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