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.

[M20S Driver]

On 11/20/2023 at 8:28 PM, Rick Junkin said:

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

Hi Rick,

Did the potentiometer fix your problem?  Mine flickers too.

Driver 

[Rick Junkin]

17 minutes ago, M20S Driver said:

Hi Rick,

Did the potentiometer fix your problem?  Mine flickers too.

Driver 

It fixed the flickering, but turns out I also have a couple of dead LED segments. I picked up some spare LED blocks and will replace the failed ones the next time I’m into the panel. I should have just R&R’d all of them when I had it apart last year.

 

[Fly Boomer]

On 11/20/2023 at 7:44 PM, 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. 

Got a pic of your M20K trim and flap indicators?  Pretty sure mine are entirely mechanical.

[MatthiasArnold]

Potentiometers tend to get „scratchy“ over time. Most of you will recall the noise when adjusting the volume on a good old analog HIFI amplifier. it’s typically a combination of dirt and wear. 
If the specs match (mechanically and electrically) it should be no big problem of replacing with new - at least from the engineering perspective (disclaimer: I’m just an engineer - not an expert on regulations..)

Best, M

[MikeOH]

I've got the 'old school' mechanical indicator that has been reliable. And, probably pretty easy to fix if it ever breaks.

I never understand implementing technology just for its own sake: took a simple pointer and replaced it with a sensor (the potentiometer), fuse, wiring, LEDs, current limit resistors...maybe more circuitry to dim the LEDs.  For what??

[Marc_B]

2 hours ago, Fly Boomer said:

Got a pic of your M20K trim and flap indicators? 

I don’t have a pic of the indicators but here are the IPC pages for trim and flap indications. It is displayed on the multifunction lens in the center console with LED boxes like @Rick Junkin has above, but 4 of them all together in one large lens that has flaps, trim, cowl flaps, elevator trim all together. 

[Fly Boomer]

21 minutes ago, Marc_B said:

here are the IPC pages for trim and flap indications

Thanks.  That's completely different to mine.  Somehow missed Rick's pic above.

[Rick Junkin]

7 minutes ago, Fly Boomer said:

Somehow missed Rick's pic above.

I added the picture on edit, wasn't there the first time you saw the post. 

[Will.iam]

For bringing back to life an intermittent Potentiometer do not underestimate the power of Deoxit electrical cleaner

it’s damn near witchcraft in a can. Had a car radio that the volume knob would have dead spots and even sometimes the volume would go down instead of up. Super annoying but i sprayed some deoxit around the knob and it wicked it’s way down to the potentiometer and within 10 seconds of turning the knob restored functionality to the volume knob and that was over 3 years ago!

https://a.co/d/bc1vgMm

a cheap 30 second try and it might get you more service life on your original equipment and save you time changing out parts. If not you haven’t lost much time or money. 

[Marc_B]

I've read that potentiometers have some dielectric grease of some type that gets washed way by contact cleaners and the general gist was that it improves the corrosion temporarily but that it speeds up the degradation of the pot.  Of course if it's a matter of kicking the can down the road to eventually replace, it might be worth it?  Seems like the internet is back and forth regarding should you clean potentiometers and how...but its seems like Deoxit is a common recommendation.

(I'm not an electrical engineer, and have no way to validate what optimal care of your potentiometers may be).

[Will.iam]

15 hours ago, Marc_B said:

I've read that potentiometers have some dielectric grease of some type that gets washed way by contact cleaners and the general gist was that it improves the corrosion temporarily but that it speeds up the degradation of the pot.  Of course if it's a matter of kicking the can down the road to eventually replace, it might be worth it?  Seems like the internet is back and forth regarding should you clean potentiometers and how...but its seems like Deoxit is a common recommendation.

(I'm not an electrical engineer, and have no way to validate what optimal care of your potentiometers may be).

By the time you are wanting to try deoxit what ever grease has failed or you would not be having the problem.  Sure replacing the component would be best but not for your wallet or time. In my case i really did not want to take the time to tear apart the dash to get the radio out to then hope i could just buy the potentiometer i needed wait on shipping with the dash all apart and thus truck out of use. 
if deoxit had not worked that would have been the path i used but it did quickly and is still working 3 years later definitely got my money and time out of that bottle for sure!