Trim/Flap potentiometer

[Marc_B]

Lately my trim and flap LED indications have been a little more jumpy with adjustments and it seems that the likely culprit is the potentiometer.  My Mooney M20K IPC shows WA2G056S502UA, Allen Bradley 5K ohm, 10% tolerance, linear potentiometer is used for both my trim and flap indication.  Curious on the typical life span for these pots and how quickly they typically go from jumpy/erratic to need for replacement.  One spec sheet I saw was life expectancy 25,000 cycles...no clue what that translates into in Mooney world.  Seems like replacement would be pretty simple. 

Also curious as I've found RV6NAYSD502A which seems like same spec different manufacturer, and LASAR website had a trim/flap potentiometer 3862C-282-502A (no clue the specs on that one)...

[LANCECASPER]

45 minutes ago, Marc_B said:

Lately my trim and flap LED indications have been a little more jumpy with adjustments and it seems that the likely culprit is the potentiometer.  My Mooney M20K IPC shows WA2G056S502UA, Allen Bradley 5K ohm, 10% tolerance, linear potentiometer is used for both my trim and flap indication.  Curious on the typical life span for these pots and how quickly they typically go from jumpy/erratic to need for replacement.  One spec sheet I saw was life expectancy 25,000 cycles...no clue what that translates into in Mooney world.  Seems like replacement would be pretty simple. 

Also curious as I've found RV6NAYSD502A which seems like same spec different manufacturer, and LASAR website had a trim/flap potentiometer 3862C-282-502A (no clue the specs on that one)...

 

[Marc_B]

@LANCECASPER I saw that post as it's one of 2 posts I could find on MS regarding trim/flaps indication issues.  But wouldn't a blown fuse mean NO indication?  I have indications they just jump around and bounce when adjusting.  What did you see with the blown pico fuse?

[LANCECASPER]

5 minutes ago, Marc_B said:

@LANCECASPER I saw that post as it's one of 2 posts I could find on MS regarding trim/flaps indication issues.  But wouldn't a blown fuse mean NO indication?  I have indications they just jump around and bounce when adjusting.  What did you see with the blown pico fuse?

The trim/flaps indicator was inop on an M20M that I bought. A few weeks earlier when I looked at the airplane they were flickering. Not sure if that would fix yours, but I thought I would throw it out there. It might be worth a call to Don Maxwell.

[PT20J]

If they are both jumpy, I'd look for a common power or ground connection problem rather than assume two pots went bad. 

[Marc_B]

@LANCECASPER makes sense.  What I'm seeing is when adjusting the trim (say from landing and hand rolling back to t/o trim) the indication moves in the right direction but not smoothly and sometimes bounces around 1-2 neighboring LED bars, or when I set t/o flaps it sometimes flutters around the bars around the t/o indication.  It moves in the right directions and all LEDs light.  One time at t/o trim it was 2 bars high, so I went down to full flaps and back to t/o and indication was accurate and stable.  Both times visual flap deployment appeared correct.

@PT20J It's not necessarily both indications simultaneously or consistently all the time.  What I've read is that a bad potentiometer results in jumping of the resistance as the wiper is stroked across the range of the potentiometer.  This seems like what I'm seeing with the light output.  Not a big issue at this point, but just curious if this just indicates wear of the pot and suggests issues upcoming.

Thanks for the help and suggestions!

[Rick Junkin]

2 hours ago, Marc_B said:

Lately my trim and flap LED indications have been a little more jumpy with adjustments and it seems that the likely culprit is the potentiometer.  My Mooney M20K IPC shows WA2G056S502UA, Allen Bradley 5K ohm, 10% tolerance, linear potentiometer is used for both my trim and flap indication.  Curious on the typical life span for these pots and how quickly they typically go from jumpy/erratic to need for replacement.  One spec sheet I saw was life expectancy 25,000 cycles...no clue what that translates into in Mooney world.  Seems like replacement would be pretty simple. 

Also curious as I've found RV6NAYSD502A which seems like same spec different manufacturer, and LASAR website had a trim/flap potentiometer 3862C-282-502A (no clue the specs on that one)...

@Marc_B My trim indicator is exhibiting the same kind of jumpy and drop out behavior consistently in a specific range on the indicator, which looks like drop out from the pot. My flap indicator works fine. I ordered this 882-RV6NAYSD502A from Mouser for about $44 including shipping. I'm going to swap it out next month during the annual and see if it clears up the issue. It's the easiest thing to get to and an easy swap. If it doesn't work the next step will be to pull the indicator and replace the pico fuses with the ones I ordered and set aside back when @LANCECASPER posted his original resolution.

Cheers,
Rick

[Marc_B]

@Rick Junkin I found a datasheet from Allen Bradley regarding potentiometers and the RV6NAYSD502A is just the Mil-R-94 designation equivalent.  Not entirely sure if there is any difference or improvement one way or the other...but looks identical spec otherwise.

Potentiometer data sheet AllenBradley.pdf

[Rick Junkin]

10 minutes ago, Marc_B said:

RV6NAYSD502A is just the Mil-R-94 designation equivalent.

Yup. The potentiometer I got from Mouser is a physical match to the one in the airplane so this will be an easy task when I get back home in a few weeks.

Cheers,
Rick

[PT20J]

2 hours ago, Marc_B said:

It's not necessarily both indications simultaneously or consistently all the time.  What I've read is that a bad potentiometer results in jumping of the resistance as the wiper is stroke across the range of the potentiometer.  This seems like what I'm seeing with the light output.  Not a big issue at this point, but just curious if this just indicates wear of the pot and suggests issues upcoming.

A pot is a mechanical device, so it is subject to wear, especially in an environment where the wiper frequently rests on one location and there is vibration. But if both are doing it, I'd still look for something common to them. On the other hand, the pot is only about $30 to replace, so it's probably easier to replace it than to spend a lot of time troubleshooting unless inspection finds a loose connection or something obvious.

Looks like someone has new/old stock on eBay for $27.50 https://www.ebay.com/itm/153892538415?hash=item23d4b5c82f:g:eL8AAOSw4A9ejyQe&amdata=enc%3AAQAIAAAAwBYA%2FsyYnycHBB74s6awH4oNvoZdB%2BtMMX2AI8zmYzY59zSvGRoSm9C6L70n23W7ZFJv7iLDsgbktElPa4GJyCoJ1N5E8BZ%2BqNLytOR5tXcjjz%2FZ%2B4OCQW%2BI5JD6A%2F6SDak8T8ROv4njhQk63zCzqwSv0MLcpT7l2O9wo2aPgcg4lydfQlgIUP0A2QZdu4ZAi3lmlfcPJv4XYPsUb25EJNf0Y520xehsWDrOUOzC0ky%2FoIpZ06hEf4nbw9O3YtJFQQ%3D%3D|tkp%3ABk9SR8rO2oX-Yg

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[LANCECASPER]

10 minutes ago, PT20J said:

A pot is a mechanical device, so it is subject to wear, especially in an environment where the wiper frequently rests on one location and there is vibration. But if both are doing it, I'd still look for something common to them. On the other hand, the pot is only about $30 to replace, so it's probably easier to replace it than to spend a lot of time troubleshooting unless inspection finds a loose connection or something obvious.

Looks like someone has new/old stock on eBay for $27.50 https://www.ebay.com/itm/153892538415?hash=item23d4b5c82f:g:eL8AAOSw4A9ejyQe&amdata=enc%3AAQAIAAAAwBYA%2FsyYnycHBB74s6awH4oNvoZdB%2BtMMX2AI8zmYzY59zSvGRoSm9C6L70n23W7ZFJv7iLDsgbktElPa4GJyCoJ1N5E8BZ%2BqNLytOR5tXcjjz%2FZ%2B4OCQW%2BI5JD6A%2F6SDak8T8ROv4njhQk63zCzqwSv0MLcpT7l2O9wo2aPgcg4lydfQlgIUP0A2QZdu4ZAi3lmlfcPJv4XYPsUb25EJNf0Y520xehsWDrOUOzC0ky%2FoIpZ06hEf4nbw9O3YtJFQQ%3D%3D|tkp%3ABk9SR8rO2oX-Yg

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That's for a 5 pack of them. That's a great deal.