AV 50,000 failure

Back in mid June my trim failed due to a blown trim fuse that feeds the AV 50,000. After much trouble shooting of the trim servo and leads I came to the conclusion that the chip on the AV board had shorted out as a new fuse would blow immediately. If I disconnected the wire to pin #9 and put in a new fuse, all was OK. The AV went back to Van's for repair but it got there a week or so before Oshkosh. The repair person stayed behind at Oshkosh to help clean up then went on vacation! I got the board back in September and it was OK for about a total of 30 minutes, two short flights plus some ground testing then the fuse was blown again. After some back and forth with Van's they sent me a new AV 50,000 which has lasted for about 3 hours before the fuse blew again today. A larger fuse (5 amps) blew when inserted. Inserting a fuse only puts power to the chip on the AV 50,000 board. From the schematic it looks like that there is nothing else on that quadrant of the chip, without the trim switch being either up or down nothing should be happening, yet it blows fuses. Anyone have any ideas where to look for this short or how to further troubleshoot the problem? I am getting very frustrated.
The RV-12 is completely standard, was signed off in 2013 and has about 100 hours on the tach. Never had any electrical problems before this came up.
Henry

Take one of those blown fuses and connect two wires to it, one on each leg. Connect those two wires to a low wattage (10 or less) automotive incandescent indicator lamp. If the lamp illuminates, there is a short circuit. Now you can troubleshoot without blowing more fuses.

Try disconnecting the Auto Pilot D-Sub connector from the AV-50000A to see if the short circuit goes away.

I don't know how adventurous you are, but I fixed same problem by installing Ray Allen 2-speed trim controller and Ray Allen rocker switch. Best thing I ever did. Zero problems. Slow speed makes setting pitch trim very easy at cruise speeds and fast trim is invaluable at slow speeds in the pattern as well as for quick reconfiguring for aborted landing.

Need good skills for this... http://www.vansairforce.com/community/showpost.php?p=1202259&postcount=299

Jim, judging by the AV-50000A, Henry has a Skyview, not a D-180. Installing the Ray Allen trim speed controller would be different in his RV-12, maybe even easier than for a D-180 system.

krazydoc33 said:

Back in mid June my trim failed due to a blown trim fuse that feeds the AV 50,000. After much trouble shooting of the trim servo and leads I came to the conclusion that the chip on the AV board had shorted out as a new fuse would blow immediately. If I disconnected the wire to pin #9 and put in a new fuse, all was OK. The AV went back to Van's for repair but it got there a week or so before Oshkosh. The repair person stayed behind at Oshkosh to help clean up then went on vacation! I got the board back in September and it was OK for about a total of 30 minutes, two short flights plus some ground testing then the fuse was blown again. After some back and forth with Van's they sent me a new AV 50,000 which has lasted for about 3 hours before the fuse blew again today. A larger fuse (5 amps) blew when inserted. Inserting a fuse only puts power to the chip on the AV 50,000 board. From the schematic it looks like that there is nothing else on that quadrant of the chip, without the trim switch being either up or down nothing should be happening, yet it blows fuses. Anyone have any ideas where to look for this short or how to further troubleshoot the problem? I am getting very frustrated.
The RV-12 is completely standard, was signed off in 2013 and has about 100 hours on the tach. Never had any electrical problems before this came up.
Henry

Click to expand...

Henry,
Sorry you are still having problems with your RV-12. Problems like this can be very frustrating to resolve.

As mentioned in the note sent with the new PCB the first time, the type of component failure you are having is likely from a short of some type in the wires that drive the servo. When one of the servo wires are shorted to ground, it can cause a failure of one of the trim control components and its failure mode is a short to ground inside of the AV-50000.

The note suggested that some detailed troubleshooting be done, because if the fault wasn't found and repaired, that the problem most likely would happen again. It sounds like it has and installing an entirely new AV-50000 has now failed in the same way.

You need to inspect the full length of the servo wire from the AV-50000 box, all the way back to the servo and see if you find a location that might be intermittently rubbing and shorting to ground. The fact that the system worked fine on the airplane for airplane for 100 hrs is a good indicator that it has probably now gotten enough flight time that at some point along the servo wire, enough rubbing has occurred that it has finally rubbed through and intermittently is shorted to ground. If it happens to be shorted at the same moment that you use the trim for that direction...... the component fails.

The most likely place for a short to ground is in the tail cone where the trim servo cable passes over a J-Stiffener. If that is the case, then installing a Ray Allen trim control will not help.

Similar situation but hope my AV5...is okay

I had a ?run away? trim experience where mine went to full Up on its own. When I started to investigate I switched White wires near the trim motor, turned the Master on, and the trim motor began running the other way when the Master was turned on. No fuse blown.
My 12 started flying in 2013, early Skyview, so I have the conversion wiring diagram.

I removed the cover to expose behind the panel. The only thing I have done was remove the plug labeled Switches in the corner of the Control Box. All ?looked? fine and I tried to add power to pins 4 or 5, trim + or - , and see what happens. Nothing so I reinserted the plug, turned on the Master, and the trim did not run on its own. The rocker switch up and down was working properly, and I was still suspicious. I preformed a ground run with no issues thinking if a short had occurred I needed some vibration to get something to happen. I did inspect all the connections in the back and there were a few connections which needed some attention. Now where the wires transition from the fuselage into the trim motor area, I moved those wires around a lot, and if one was shorting near this location I might have just moved it from where it?s grounding?

I did make one flight, which had a lot of taxi time too, so far the trim operated normally.
Since the switch gets a lot of the activity I guess my hope was a bad switch. Do these switches pull out of the panel? When I received the switches they were all installed and labeled in a nice subpanel as all builders know, and I didn?t mess with them. I saw where Jim modified his trim system, cool, but I don?t have the experience removing a switch in this plane. The switches I installed in my RV6 most had plastic spring clips, top and bottom, which needed to be pushed down to push a plug out from the back. Anyway some insight would be appreciated about the situation and the plug installation. Thanks

Thanks for all the insights. I had come to the conclusion that there was probably a intermittent short some where that was burning out the IC on the AV board, just did not want to believe it! Knowing that this has happened before is a BIG help. Takes it from improbable to possible. When the repaired board did come back from Van's there was no trouble shooting suggestions.
I will run a new pair of shielded wires from the trim switch directly to the trim servo, not hard to do just grunt work. I don't think that shielded wire is needed but it will add another layer of protection. Will replace the servo at the same time as I do have one available. My system is the change over one from the D180 to the Skyview, it has the conversion harness to contend with. The early schematics do not show any traces on the AV board so I have been using the later version ASSUMING that the boards are identical. The other unknown is the trim switch wiring. The schematic only shows one wire, ground, to the switch and no power line? I will wire directly from the trim fuse to the switch and remove the wire to pin #9 on the AV board connector. Will have to wait and see if the servo is too fast or slow. Any comments on this "work around" will be most helpful.
I will post the results when I am done.
Henry

Henry, your intended wiring changes are doable. Just be careful how you wire the switch. It should be completely disconnected from Van's circuit board. The servo motor should connect to the switch common (com) terminals. The switch N.O. and N.C. terminals need to be wired to plus and minus so that polarity to the motor can be reversed. At aircraft cruise speed, the trim motor will run too fast when connected directly to 12 volts. I do not know how well a series resistor would work. You could try a 5 - 10 ohm resistor to see what happens. The motor might not have enough torque to start up with a resistor in series.
Trim motor speed controllers modify direct current to pulsing direct current (PWM) to reduce the motor speed.