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Panel dimmers - repair or buy PWM


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Hi guys,

I have one if these dual channel rheostat dual dimmers but it flickers at some percentages. So I end up with slightly brighter or slightly dimmer settings which isn't a problem but becomes one after 3hrs in the dark.

https://www.aircraftspruce.com/catalog/elpages/maxdimminid.php?clickkey=108153

Has anyone fixed these successfully? I think it's just some corrosion spots on the rheostats so maybe clean them or replace them?

Also, are there any TSO constant-current output (preferably not pwm but a buck converter) dimmers out there? My "outer channel" only controls the lighting on one ki209 so I don't mind switching to single channel. 

Thanks...

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Fixing the Mooney dimmer depends on what’s wrong with it. Your symptoms sound like worn potentiometers. 

I don’t believe there is a TSO for dimmers.

Seaton has an STC for the MaxDim, so your IA would fill out a 337.

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Thanks.  I tried opening the STC document, but the link was dead. 

How is this thing a "major alteration"?  It doesn't affect anything regarding flight characteristics, limitations, weight or CG.  Why is it not a minor alteration that any AP can sign off?

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14 minutes ago, FlyingDude said:

Thanks.  I tried opening the STC document, but the link was dead. 

How is this thing a "major alteration"?  It doesn't affect anything regarding flight characteristics, limitations, weight or CG.  Why is it not a minor alteration that any AP can sign off?

I’ll echo PT20J’s opinion that it’s the pots based on your symptoms. Mine died but I found a pinched wire within the control box that was easily repaired. Most components could be sourced but I believe the transistors are ancient germanium ones! They could be a problem to find! Doubt they are your issue.

As far as why a “major alteration”…when someone explains why I need a PMA landing light bulb when, for Part 91, a landing light isn’t even needed, you’ll have your answer :D

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I believe the FAAs logic is that the part has to somehow be approved for installation an a certificated aircraft. Standard parts like nuts and bolt made to an industry standard are approved. Parts made or specified by the airplane manufacturer are approved. The FAA sometimes approves parts that have the same form, fit and function with just a PMA (for instance GLAP windshields).  But something like a generic light dimmer usually gets approved through the STC process. And by definition, since it is a supplement to the type certificate, the FAA considers it a major alteration requiring a 337.

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3 minutes ago, MikeOH said:

I’ll echo PT20J’s opinion that it’s the pots based on your symptoms. Mine died but I found a pinched wire within the control box that was easily repaired. Most components could be sourced but I believe the transistors are ancient germanium ones! They could be a problem to find! Doubt they are your issue.

As far as why a “major alteration”…when someone explains why I need a PMA landing light bulb when, for Part 91, a landing light isn’t even needed, you’ll have your answer :D

That would be a non-answer.  "Because I said so" and "let's err on the side of caution" ... are not real answers.

I read these good articles regarding minor alterations:

https://www.aopa.org/news-and-media/all-news/2014/october/08/aircraft-maintenance-major-vs-minor-alterations

https://www.aopa.org/news-and-media/all-news/2014/october/22/aircraft-maintenance-major-vs-minor-alterations-part-2

The author also mentions how FAA rejected some 337 forms because those alterations were minor and not major, hence no 337 was required.

The alteration must be insignificant (no changes in performance, weight, etc.) and you need supporting documents.  PMA is a good supporting document.  Lacking which, you need other test results, production data, quality data, etc. to show that the part exceeds the usual aircraft specs.  So, for your landing light, you need to show data that it's not some dirt cheap piece of crap product that will potentially cause trouble; and you need to prove that it's higher quality than the other PMA part out there ... (Just parroting my AP/IA).

 

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There is a legal opinion letter from the FAA (Bowers) that suggests that a 337 is not required for an STC that is not a major alteration.   It kind of does make one wonder why an STC would exist if it wasn't a major alteration, and the line between major and minor can certainly be pretty broad and controversial, so perhaps that's not too surprising.

A 337 isn't too big of a deal assuming a cooperative IA is within easy reach, which is sometimes a significant hurdle for people.

 

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In my experience, you absolutely, positively cannot understand the FARs without also reading the legal opinions because there are sometimes opinions that directly contradict the wording of the law. And, you cannot understand how the FAA works without reading its various Order documents that provide guidance to FAA personnel. And, what normal person can keep up with all that? "Why?" questions frequently don't have satisfying answers when dealing with the FAA or Microsoft. It's easier to go with the flow and just go with it. As Don Maxwell once said, "It's only a piece of paper."

 

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1 hour ago, EricJ said:

There is a legal opinion letter from the FAA (Bowers) that suggests that a 337 is not required for an STC that is not a major alteration.   It kind of does make one wonder why an STC would exist if it wasn't a major alteration, and the line between major and minor can certainly be pretty broad and controversial, so perhaps that's not too surprising.

A 337 isn't too big of a deal assuming a cooperative IA is within easy reach, which is sometimes a significant hurdle for people.

 

I read the interpretation and I see why you said "suggests". The opinion states that "an STC is design approval for a major change". Then it goes on to state the legal definition of major and minor changes. Then it says if you use an STC to make a major change, you need to file a 337. It never explicitly says that if you use an STC to make a minor change that you do not need to file a 337. It might be implied, but it doesn't explicitly state that. What it actually implies to me is that a STC should not be used to approve minor changes. But it has long been the policy of some regions to do so. Really what the FAA should do is create something like an STC for minor alterations that gives approval basis for installation without any ambiguity about a 337.

Skip

Bowers_2016_Legal_Interpretation.pdf

 

 

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43 minutes ago, PT20J said:

I read the interpretation and I see why you said "suggests". The opinion states that "an STC is design approval for a major change". Then it goes on to state the legal definition of major and minor changes. Then it says if you use an STC to make a major change, you need to file a 337. It never explicitly says that if you use an STC to make a minor change that you do not need to file a 337. It might be implied, but it doesn't explicitly state that. What it actually implies to me is that a STC should not be used to approve minor changes. But it has long been the policy of some regions to do so. Really what the FAA should do is create something like an STC for minor alterations that gives approval basis for installation without any ambiguity about a 337.

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Bowers_2016_Legal_Interpretation.pdf 1.85 MB · 0 downloads

 

 

Yes, in a paragraph about Type Design they state, "An STC is a design approval for a major change in type design," and then cite FARs from Part 21,  which is about products and part certifications, not airplane maintenance.    The next paragraph talks about how STCs apply to airplanes, and states, "Therefore an alteration done in accordance with an STC would constitute a major alteration if..." and cites the usual definitions of "major alteration" and cites 14 CFR 1.1, which defines a major alteration, and then states, "Any such alteration would require completion of FAA Form 337."

So it seems to be consistent about the requirement for a 337 being whether or not it is a major alteration, and cites the usual definitions of major alteration without an STC being a requirement or a triggering characteristic.   The "if" seems telling to me, but, yeah, they don't come out and specifically say an STC doesn't automatically require a 337.  I've not seen anything that requires a 337 to go with an STC if the STC isn't a major alteration, but I suspect this is one of those areas where two FSDOs could look at the same thing and disagree.

 

 

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10 minutes ago, EricJ said:

Yes, in a paragraph about Type Design they state, "An STC is a design approval for a major change in type design," and then cite FARs from Part 21,  which is about products and part certifications, not airplane maintenance.    The next paragraph talks about how STCs apply to airplanes, and states, "Therefore an alteration done in accordance with an STC would constitute a major alteration if..." and cites the usual definitions of "major alteration" and cites 14 CFR 1.1, which defines a major alteration, and then states, "Any such alteration would require completion of FAA Form 337."

So it seems to be consistent about the requirement for a 337 being whether or not it is a major alteration, and cites the usual definitions of major alteration without an STC being a requirement or a triggering characteristic.   The "if" seems telling to me, but, yeah, they don't come out and specifically say an STC doesn't automatically require a 337.  I've not seen anything that requires a 337 to go with an STC if the STC isn't a major alteration, but I suspect this is one of those areas where two FSDOs could look at the same thing and disagree.

 

 

Which, of course, is the problem with trying to get a consistent answer because the FAA delegates so much decision authority to the FSDOs and they don’t all agree. What one region allows, another may prohibit. 

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1 hour ago, PT20J said:

FAA should do is create something like an STC for minor alterations that gives approval basis

Or, clarify what's already written without extra burden. If it doesn't alter the plane and if you have documentation to prove that it's good quality (won't shatter, won't cause EMC issues, won't start a fire, won't corrode anything it touches), then let it to the AP to sign it off. APs can already use stuff that exceed the usual parts' standards.

 

2 hours ago, PT20J said:

As Don Maxwell once said, "It's only a piece of paper."

So is money...

I like Mike B and he actually even had a seminar called "Keep it Minor".

 

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I had the left mag replaced with a SureFly using the STC and the installer filed the 337. Later, I had the SureFly removed and the mag reinstalled and the IA said that we didn’t need a 337 for that. I always wondered why. At least the  Bowers opinion explains that:

“Regardless of the type of STC, the approved design change does not become part of the specifications ofa particular aircraft, aircraft engine, or propeller until the particular aircraft, aircraft engine, or propeller has been altered in accordance with the STC.”

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I had the left mag replaced with a SureFly using the STC and the installer filed the 337. Later, I had the SureFly removed and the mag reinstalled and the IA said that we didn’t need a 337 for that. I always wondered why. At least the  Bowers opinion explains that:
“Regardless of the type of STC, the approved design change does not become part of the specifications ofa particular aircraft, aircraft engine, or propeller until the particular aircraft, aircraft engine, or propeller has been altered in accordance with the STC.”

Your scenario opens up an interesting question. If an AD was issued for the SureFly version that was installed in your plane but removed and it called for an immediate grounding, does the FAA consider your plane grounded since the documentation they have indicates it is in your plane?

Or are you good to go because you have the original mag in the plane even though the modifying 337 was not rescinded? It seems sometimes paperwork can create more confusion.


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19 minutes ago, Marauder said:


Your scenario opens up an interesting question. If an AD was issued for the SureFly version that was installed in your plane but removed and it called for an immediate grounding, does the FAA consider your plane grounded since the documentation they have indicates it is in your plane?

Or are you good to go because you have the original mag in the plane even though the modifying 337 was not rescinded? It seems sometimes paperwork can create more confusion.


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The way I read it, you are good to go. The 337 allows you to make the modification, but the airplane isn't altered until the modification is completed and a logbook entry made. And, if you undo the modification and make a logbook entry, the airplane is back in it's original configuration. You could then redo the modification at some future point without filing another 337. So the 337 allows you to make a change, but it isn't the record of the change; the logbooks are the record.

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10 hours ago, Marauder said:


Your scenario opens up an interesting question. If an AD was issued for the SureFly version that was installed in your plane but removed and it called for an immediate grounding, does the FAA consider your plane grounded since the documentation they have indicates it is in your plane?

Or are you good to go because you have the original mag in the plane even though the modifying 337 was not rescinded? It seems sometimes paperwork can create more confusion.

If the aircraft logbook indicates that it was removed and/or an inspection verifies that it isn't there, the AD doesn't apply. 

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If the aircraft logbook indicates that it was removed and/or an inspection verifies that it isn't there, the AD doesn't apply. 

That was the reason for my question. It sounds like if an emergency “do not fly” AD was issued, then until the plane and/or logbook was reviewed, presumably by an IA, you would be grounded. I get that right?


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5 minutes ago, Marauder said:


That was the reason for my question. It sounds like if an emergency “do not fly” AD was issued, then until the plane and/or logbook was reviewed, presumably by an IA, you would be grounded. I get that right?


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There should be instructions on the AD for applicability and method of compliance.   An AD has an applicability section that may say something like "with X installed", and if it isn't installed then it doesn't apply.   If the applicability is by S/N or model or something and the method of compliance describes an inspection for the item, then that inspection has to be performed if the S/N or other applicability description applies.  If it is known that it doesn't apply by the applicability criterion then it's not an issue, but if it isn't known then it should be checked.   Usually at the next annual any potentially relevant ADs are added to the compliance list with an explanation of "not installed" or "S/N doesn't apply" or something similar so there's a record that it was checked.   If an inspection is required by the compliance description then that has to be done and recorded as part of the compliance.  

So the AD has to be read to see whether it is applicable by the applicability description, and if it is then the compliance instructions come into play and the results have to be recorded.   If not then nothing needs to be done but it should be put on the AD compliance list for the aircraft to record that it was checked.

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One thing to consider when filling out and filing a FAA Form 337 is that by doing so the Mechanic just made what ever action taken into a "Major".   So by calling the maintenance action a "Major Repair/Alteration" there must be approved data to accompany the 337.   For an STC that is easy as it is already approved for other aspects it can be more difficult.   Many different ways to obtain this supporting data (Field Approval, DER approval with FAA Form 8110, DAR....ect.) but an A&P Mechanic alone (Holding only an A&P / IA)  can not create approved data without additional steps like those listed above.

I have seen many posts on Mooney Space that stated their mechanic installed something (not having STC or other approved data) and just filled out a 337 to make it legal so it would not get flagged by another IA later down the road.    Always wondered how this was accomplished?

Warren 

FAA A&P, IA, DAR

 

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1 hour ago, Old Chub said:

One thing to consider when filling out and filing a FAA Form 337 is that by doing so the Mechanic just made what ever action taken into a "Major".   So by calling the maintenance action a "Major Repair/Alteration" there must be approved data to accompany the 337.   For an STC that is easy as it is already approved for other aspects it can be more difficult.   Many different ways to obtain this supporting data (Field Approval, DER approval with FAA Form 8110, DAR....ect.) but an A&P Mechanic alone (Holding only an A&P / IA)  can not create approved data without additional steps like those listed above.

I have seen many posts on Mooney Space that stated their mechanic installed something (not having STC or other approved data) and just filled out a 337 to make it legal so it would not get flagged by another IA later down the road.    Always wondered how this was accomplished?

Warren 

FAA A&P, IA, DAR

AC 43.13 is approved repair data when it is not contrary to manufacturer's data.    This is Paragraph 1, PURPOSE, of the first page of AC 43.13, but many people don't know it's there.   It probably doesn't cover a lot of mods, but, sometimes, I suppose...

But otherwise I'm with you, I don't know what people are doing with so many 337s.

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You can also install a dimmer using the AC about parts and substitutions for aging aircraft.  There is also way too much classifying minor alterations as major. Here is their definition right out of the AC 

 

Note: You should also review 14 CFR part 43, Appendix A, for expanded definitions
and examples ofMajor Repairs to airframes,powerplants,propellers and appliances.
b. Major Alteration. 14 CFR part 1, § 1.1 General definitions, defines a Major alteration as an alteration not listed in the aircraft, aircraft engine, or propeller specifications and meets one of the following conditions:
(1) The alteration might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or
(2) The alteration is not done according to accepted practices or cannot be done by elementary operations.
Note: You should also review 14 CFR part 43, Appendix A, for expanded definitions and examples ofMajor Alterations to airframes, powerplants, propellers and appliances.

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back to the original question.   It would be possible to remove the transistors and little bitty fuses and just use the existing rheostats.   The range of dimming would not be be as large as with the rheostats.   Some of the rheostats have an off switch on them.   Some of the models have a red and white set of lights.

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The transistors get blown whenever the people short the output leads on the side of the glareshield when they don't hook it back up to put the glareshield back in.  Will the transistors blow up and over the output leg of the transistor shorts against the hole drilled in the metal for the heat sink, that heat shrink tubing shrinks back and exposes the metal . Personally, If mine goes bad I'm putting in a maxdim duo. 

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