Why would avionics backlighting pulse?

Banjo33

Banjo33

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Banjo33
I have a EI CGR combo in my plane. It has the light sensor that auto dims the engine instruments as the light conditions change. At night, the digital displays “pulse.” It does it during the day as well, but it’s not noticeable unless you’re specifically looking for it, but at night it’s very apparent. I’ve turned all exterior lights off (strobes, beacons, etc) to ensure they aren’t responsible, but haven’t looked beyond there. It has done this since install, but I don’t normally fly at night, so out of sight/out of mind and all that and very low on the list of priorities. Any thoughts as to where this could be originating from or where to troubleshoot?

Edit to add: when I say “pulse”, I mean bright to dim and back, almost rhythmically. Like when the interior lights of your car switch from daytime to nighttime mode when you drive under an overpass and back out the other side. Not on/off/on….
 
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My first thought would be inconsistent power source, such as a voltage regulator issue, weak battery, or failing alternator. Good luck.
 
Does it do it on the ground when the engine isn't running (just running off the battery)?
 
Dana said:
Does it do it on the ground when the engine isn't running (just running off the battery)?
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I’m not certain…. I’ve only flown the plane at night once since I had it installed and it’s almost imperceptible during the day.
 
So... to exclude any external influence, put a piece of black electrical tape over the sender, followed by a piece of aluminum tape, if you have some.
If you still see pulsing, turn the alternator off, as well as any high intermittent electrical loads (strobes, anti-collision light). It could be that your unit is sensitive to bus voltage fluctuations. If that doesn't cure it, the backlight driver in your unit might be faulty.
 
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AV8R_87 said:
So... to exclude any external influence, put a piece of black electrical tape over the sendor, followed by a piece of aluminum tape, if you have some.
If you still see pulsing, turn the alternator off, as well as any high intermittent electrical loads (strobes, anti-collision light). It could be that your unit is sensitive to bus voltage fluctuations. If that doesn't cure it, the backlight driver in your unit might be faulty.
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Great advice, thanks! Will give it a shot this week.

I also have a message in with EI support to see their thoughts too and will post that here if it’s pertinent.
 
Banjo33 said:
I have a EI CGR combo in my plane. It has the light sensor that auto dims the engine instruments as the light conditions change. At night, the digital displays “pulse.” It does it during the day as well, but it’s not noticeable unless you’re specifically looking for it, but at night it’s very apparent. I’ve turned all exterior lights off (strobes, beacons, etc) to ensure they aren’t responsible, but haven’t looked beyond there. It has done this since install, but I don’t normally fly at night, so out of sight/out of mind and all that and very low on the list of priorities. Any thoughts as to where this could be originating from or where to troubleshoot?

Edit to add: when I say “pulse”, I mean bright to dim and back, almost rhythmically. Like when the interior lights of your car switch from daytime to nighttime mode when you drive under an overpass and back out the other side. Not on/off/on….
Click to expand...

Do the lights pulse with engine off, alternator master off, battery master on, all other electrical switches off?
Do the lights pulse engine running, battery and alt master on, all other switches off?
Do the lights pulse when you turn on a switch such as the collision lights?

This will allow you to isolate the problem.

My guess is a bad diode in the alternator or a bad ground on an anticollision light.
 
Banjo33 said:
I’ve only flown the plane at night once since I had it installed
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If this is a recent installation you may want to check into the warranty periods for the install and the equipment. There's always a risk of voiding your warranties by going the DIY route.
 
Clip4 said:
Do the lights pulse with engine off, alternator master off, battery master on, all other electrical switches off?
Do the lights pulse engine running, battery and alt master on, all other switches off?
Do the lights pulse when you turn on a switch such as the collision lights?

This will allow you to isolate the problem.

My guess is a bad diode in the alternator or a bad ground on an anticollision light.
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They still pulse with all exterior lighting (strobes, acoll, navs….all of them) off. It does it with engine running and not running. I haven’t tried it with the alternators off and engines running, but the alternators are off when the engines aren’t running and the instruments still pulse, so I would assume the instruments will still pulse. I think the issue is in the wiring, as it’s all three displays doing it, so likely not an instrument issue.
 
Use an analog meter to check the voltage at your aux power supply socket. Does the voltage pulse?
LED light dimming is often done with very fast Pulse With Modulation circuits that vary pulse width duty cycle to try and match an incandescent light resistive dimming curve. Could be something there. Is there a program pin or a software/firmware setting for dimming that can be changed?
 
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Is the pulsing consistent with a warning light if you have them? Press the E button and see if it steadies. I had the same issue and even relocated the dimming sensor with no change. Then I read the manual. Not saying yours doesn’t have an issue, just based on my experience
 
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The dimmer input signal circuit is very sensitive to voltage changes...$0.02
 
Definitely the easy way to eliminate the sensor as a possibility is to cover it and/or shine a bright light right into it and see if it still happens.

That said, I'd agree with others that it's likely an issue with something else on the airplane causing fluctuations.

Can you use a timer and count pulses for a minute or so and see what the period of the fluctuation is? Is it consistent?
 
So, it is....

Pulsing with the engine off, and everything else turned off, and the photo cell is covered?
 
bnt83 said:
might need to contact EI
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Or maybe ET - trying to send you a message?

To be serious - what in the world could be going on except maybe a bad photo cell light level.
 
TiltOn22 said:
Did you find the issue with this?
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I’ve flown twice since posting and the pulsing has stopped. Now I don’t know if it’s an intermittent issue or, as TimBeck2 mentioned above, possibly due to an active warning or caution at the time causing it. The pulsing is similar (possibly the same) as what occurs when that happens, so it is possible.
 
Banjo33 said:
I’ve flown twice since posting and the pulsing has stopped. Now I don’t know if it’s an intermittent issue or, as TimBeck2 mentioned above, possibly due to an active warning or caution at the time causing it. The pulsing is similar (possibly the same) as what occurs when that happens, so it is possible.
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Could be charging system related, I wouldn't bother.
 
Bad ground? Even internally…. WAY back in the day I was famous for fixing all sort of weird electronic problems in the air wing (other pilots personal stuff) by taking apart and looking for bad soldered ground connections or not so tight screws that were responsible for grounding.
 
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