Strange symptoms in elevator (JR 8611A & Matchbox)

[Jarsu]

I have had some scary moments during the last few flights with my 86" QQ Yak since suddenly the elevator went to full down (regardless of dual rate settings) for a short moment and then came back. Earlier there were some failsafe glitches with the radio system but they seem to be sorted now, since the problem is now only in the elevator channel and the symptoms are very different from a normal failsafe situation. I've tried two different receivers (both Futaba PCM) and they both work in other planes so that doesn't seem to be the problem. This plane has worked well for a bit under 100 flights (except for a worn throttle servo that has been changed now).
So, my suspicions now point to either the Matchbox or the elevator servos. The Matchbox unit should get enough power since the other output of my Powerbox dual regulator goes directly to it. The servos are used for about 100 flights now so they aren't that old either, and as they both go down during the problem it should't be them. Has anyone had similar problems?

[rcairflr]

Also take a very good look at any extensions hooked to this servo, I've seen an extension cause this same problem

[Reza]

Jarsu,


Did this happen to both elevators. Are you running only one channel on the elevators with a matchbox?
What PB regulators are you referring to?

Check the extensions and connectors as was noted but give me more details on above.

Thanks,
Reza

[Reza]

One more question what receiver were you using at a time? Did you have your PB upgraded for new Futaba low signal voltage compatibility?

[Jarsu]

Rcairflr and Reza,

The receivers used are R149DP and R148DP. Powerbox model is Sensor (http://www.modellbau-deutsch.com/e/p...nsor/start.php) so it's just a dual switch with dual regulators. All the extensions are soldered (and checked )
It happened to both elevators, and I'm using one channel from the receiver with a Matchbox. I have to use it because my transmitter (Futaba 7C) doesn't offer a feasible dual elevator servo mix.

[DKjens]

Have you tried not using the extra power lead to the machbox? try not using that (your elevator servos should get enough power through the one lead). Plug the extra lead into your receiver on an open channel (if available) or Y it in with your rudder servo channel.

[Jarsu]

I'll have to try that. Also I'm not 100% sure that it is both servos that move but the downward movement seems so strong that it doesn't seem to be possible with only one servo. There is no rolling motion either. I might find out if a servo is causing the problem by swapping the left and right elevator servos and see if the pitching motion happens upwards(?)

[Jarsu]

I think I found the reason for all the glitching. The shielding of the spark plug cable was almost all the way broken (just a few strands still connected) under the shrink wrap of the spark plug cap. Now that it's fixed, let's hope the problems are gone.

[Jarsu]

Old thread, I know.... but if this helps anyone, the problem was as described in the second last message. After sending the ignition box to be repaired and getting it back -> everything works ok now. It wasn't really fixed before the whole ignition coil and cable had been replaced.

The initial reason was that I wasn't careful enough when attaching and shielding the spark plug cable. It got sheared against the cowling and it really doesn't take too many flights to do that against a fiberglass cowling. So make sure you mechanically shield and and attach the spark plug wire so that it doesn't vibrate or rub against anything.

[jonathanmanopla]

man that its not nice what are happening to you
tell me what you gonna do to know for the future of all
this problem can pass to all