Varying panel light intensity in J

[0TreeLemur]

Took my co-pilot for her first flight in our "new" J Saturday.  After the sun set we turned east and got to see a very big beautiful full moon.  She said "reminds me of our first date". 

A while later she asked: "Why is the brightness of the panel lights changing?".  "Good question- I dunno." I replied.

Both the instrument post lights and the glare shield lights were dimming and brightening with something like a 3 second periodicity.   Brighter for 3 seconds, then dimmer for 3 seconds.

Anybody seen this before?

Yesterday I crawled under the panel and observed that it seems to use the factory dimmer with the obsolete transistors.

Thx.

Fred

[T. Peterson]

23 hours ago, 0TreeLemur said:

Took my co-pilot for her first flight in our "new" J Saturday.  After the sun set we turned east and got to see a very big beautiful full moon.  She said "reminds me of our first date". 

A while later she asked: "Why is the brightness of the panel lights changing?".  "Good question- I dunno." I replied.

Both the instrument post lights and the glare shield lights were dimming and brightening with something like a 3 second periodicity.   Brighter for 3 seconds, then dimmer for 3 seconds.

Anybody seen this before?

Yesterday I crawled under the panel and observed that it seems to use the factory dimmer with the obsolete transistors.

Thx.

Fred

A lot of smart fella’s will chime in here with the exact technical advice that you need to fix the instrument lights. My experience is that panel lighting inconsistency is one of the most consistent things across aviation in a multitude of different airplanes, big, small, young or old. Those rheostats seem to just dare you to find the setting you want without flickering or self adjusting to something else.

 I say all this to encourage you not to allow the instrument lighting to diminish the wonderful experience of taking your “co-pilot for her first flight in our new J.” Her comment, “reminds me of our first date”, is the wonderful significance of that flight and is the real stuff of life. Don’t let panel lights detract from that moment.

Maybe that’s too mushy for Mooneyspace, but I guess as I age I am just becoming more of a sentimental old fool, but I kind of wish it had happened a little sooner.

[LANCECASPER]

On 1/9/2023 at 8:20 AM, 0TreeLemur said:

Took my co-pilot for her first flight in our "new" J Saturday.  After the sun set we turned east and got to see a very big beautiful full moon.  She said "reminds me of our first date". 

A while later she asked: "Why is the brightness of the panel lights changing?".  "Good question- I dunno." I replied.

Both the instrument post lights and the glare shield lights were dimming and brightening with something like a 3 second periodicity.   Brighter for 3 seconds, then dimmer for 3 seconds.

Anybody seen this before?

Yesterday I crawled under the panel and observed that it seems to use the factory dimmer with the obsolete transistors.

Thx.

Fred

Just a shot in the dark, are you hearing any radio noise in addition to the dimming? Just wondering about your alternator maybe starting to go. 

If it does end up being just the dimmers, it might be better to go to a more modern dimming solution rather than trying to repair the electronics in the box:

https://www.aircraftspruce.com/catalog/elpages/maxDimUnit.php?clickkey=4042

https://www.aircraftspruce.com/catalog/elpages/pwmdimmer.php?clickkey=4042

[goalstop]

For once, I think I may be able to contribute something to the forum!

I had the same problem in my E model.  The fluctuating varied with engine RPM, at around a 1-3 second interval at cruise.  All my interior lights were affected, but not my GPS/G5/etc.

First, I thought the master switch might be a problem... and if you have a split switch, it may be, but in my M20E it's a single switch.  Check out Don Maxwell's article here: https://www.donmaxwell.com/fluctuating-ammeters.  I tried replacing it anyway, but to no avail.

Next, we re-soldered one of the transistors.  Mechanic said it had a bad connection and this should fix the issue.  We also replaced the master battery solenoid, which had corroded and stuck open (don't think that was the issue, but we needed to replace it anyway)

Flying Friday to test the fix, and will report findings

 

[PT20J]

Might be fluctuating bus voltage.

[0TreeLemur]

53 minutes ago, goalstop said:

For once, I think I may be able to contribute something to the forum!

I had the same problem in my E model.  The fluctuating varied with engine RPM, at around a 1-3 second interval at cruise.  All my interior lights were affected, but not my GPS/G5/etc.

First, I thought the master switch might be a problem... and if you have a split switch, it may be, but in my M20E it's a single switch.  Check out Don Maxwell's article here: https://www.donmaxwell.com/fluctuating-ammeters.  I tried replacing it anyway, but to no avail.

Next, we re-soldered one of the transistors.  Mechanic said it had a bad connection and this should fix the issue.  We also replaced the master battery solenoid, which had corroded and stuck open (don't think that was the issue, but we needed to replace it anyway)

Flying Friday to test the fix, and will report findings

 

Great contribution!   FAQ worthy.   I read Don's article and it seems to describe what I'm seeing to a T.   I'll try cleaning those contacts and see if it fixes the problem.  If it does, it will be about the cheapest repair for what I was expecting to be an expensive problem!

Thanks,

Fred

[mcarterak]

On 1/10/2023 at 7:05 AM, goalstop said:

Next, we re-soldered one of the transistors.  Mechanic said it had a bad connection and this should fix the issue.  We also replaced the master battery solenoid, which had corroded and stuck open (don't think that was the issue, but we needed to replace it anyway)

Which transistor did you re-solder?

[goalstop]

The middle one I think if that helps? My mechanic did it… I forget exactly what he said

[Will.iam]

On 1/10/2023 at 10:00 AM, 0TreeLemur said:

Great contribution!   FAQ worthy.   I read Don's article and it seems to describe what I'm seeing to a T.   I'll try cleaning those contacts and see if it fixes the problem.  If it does, it will be about the cheapest repair for what I was expecting to be an expensive problem!

Thanks,

Fred

I wonder if a squirt of deoxit on the back side of the master switch would clear that up? Worked wonders on my volume control knob. 

[mooniac15u]

I chased a similar problem for a while.  We focused on the master switch based on the many threads here and Don's writeup.  That didn't fix it.  Eventually we replaced the voltage regulator and that finally fixed it.

[PT20J]

Before tearing into anything, I would get a voltmeter and determine if the electrical bus voltage is varying or just the lights. That will tell you whether it’s the dimmer or something affecting the whole electrical system. 

[mooniac15u]

37 minutes ago, PT20J said:

Before tearing into anything, I would get a voltmeter and determine if the electrical bus voltage is varying or just the lights. That will tell you whether it’s the dimmer or something affecting the whole electrical system. 

If it's the master switch or voltage regulator you can usually see rhythmic fluctuations in the ammeter that correspond with the changes in lighting.

[jaylw314]

On 1/10/2023 at 8:00 AM, 0TreeLemur said:

Great contribution!   FAQ worthy.   I read Don's article and it seems to describe what I'm seeing to a T.   I'll try cleaning those contacts and see if it fixes the problem.  If it does, it will be about the cheapest repair for what I was expecting to be an expensive problem!

Thanks,

Fred

I ran into this myself when I first got the plane.  Quick cleaning and reconnecting the leads fixed it.

It seems to be a pretty common problem with the master switch on J's, not sure how commonly it affects other models.

FWIW, it is a good idea to get a few extra fuses for the panel lights.  I've found that if I crank up one of the light rheostats too quickly, it blows the fuse, and they're hard to find

Edited January 12, 2023 by jaylw314

[0TreeLemur]

10 hours ago, jaylw314 said:

I ran into this myself when I first got the plane.  Quick cleaning and reconnecting the leads fixed it.

I wonder if there is some way to help protect that connection from future corrosion.   Dielectric grease?

Didn't realize the panel lites had fuses rather than CBs.  I'll have to look at that.   Are those fuses inside the dimmer module?   Do the two "knobs" on the bottom of the dimmer box house fuses?

Thx.

[PT20J]

Maybe this will help.

[0TreeLemur]

On 1/12/2023 at 4:29 PM, PT20J said:

Before tearing into anything, I would get a voltmeter and determine if the electrical bus voltage is varying or just the lights. That will tell you whether it’s the dimmer or something affecting the whole electrical system. 

Skip- where would you measure that?

Thanks

Fred

[PT20J]

The cigar lighter or the aux bus bar on the pilot’s side rocker switches are easy access points to measure the bus voltage. The light connector at the glare shield is an easy place to measure the light voltage for the glare shield lights.

[jaylw314]

20 hours ago, 0TreeLemur said:

I wonder if there is some way to help protect that connection from future corrosion.   Dielectric grease?

Didn't realize the panel lites had fuses rather than CBs.  I'll have to look at that.   Are those fuses inside the dimmer module?   Do the two "knobs" on the bottom of the dimmer box house fuses?

Thx.

Yeah, like @PT20J showed, they look like two knurled brown plastic knobs right under the rheostats.  Easy to get to, annoying to source.

[0TreeLemur]

Resolved!   Happy to report that cleaning the contacts on the master switch seems to have fixed the problem.   The ammeter is stable, and the brightness of the panel lights remains steady.  Thanks for helping me out @goalstop and @PT20J.