Nav/Strobe Fuse Powers PFD/MFD Dimming Circuit

[henrysamson]

So, I guess the dimming circuit has to get power from somewhere and in my RV-12iS it comes through the Nav/Strobe fuse. A few days ago the Nav/Strobe fuse blew and the PDF and MFD screens (Garmin G3x Touch) became so dim that we thought that THEY had lost power or died. It was a sunny day and we could not see anything on the screens. The fuse did light up so we knew the source to the problem fairly quickly and changed the fuse. I repeated the failure in the hangar (by pulling the fuse) where the light level is lower and the screens are functioning but are barely readable. I don't know why the fuse blew. The aircraft had about 15 hours on it at that point so maybe it was just a bad fuse. It happened just as the airplane touched down.

Just putting this out there to see if anyone else has experienced this and has any comments or suggestions. Yes, this is all handled by the AV-60000 module. I'm wondering if there is a way to set the lowest possible brightness level on screens so if this were to happen again they would still be readable.

Henry

 

[lr172]

So, I guess the dimming circuit has to get power from somewhere and in my RV-12iS it comes through the Nav/Strobe fuse. A few days ago the Nav/Strobe fuse blew and the PDF and MFD screens (Garmin G3x Touch) became so dim that we thought that THEY had lost power or died. It was a sunny day and we could not see anything on the screens. The fuse did light up so we knew the source to the problem fairly quickly and changed the fuse. I repeated the failure in the hangar (by pulling the fuse) where the light level is lower and the screens are functioning but are barely readable. I don't know why the fuse blew. The aircraft had about 15 hours on it at that point so maybe it was just a bad fuse. It happened just as the airplane touched down.

Just putting this out there to see if anyone else has experienced this and has any comments or suggestions. Yes, this is all handled by the AV-60000 module. I'm wondering if there is a way to set the lowest possible brightness level on screens so if this were to happen again they would still be readable.

Henry

I skipped the external dimming option for fear of exactly this type of scenario. It is not really that big of a hassle to dim via the knobs and buttons imo.

 

[BobTurner]

Putting the dimmer on the strobe fuse seems a poor design. Run it thru its own, dedicated fuse.

 

[henrysamson]

As a follow up to my original post . . .

I have examined the wiring diagram for the RV-12iS with the Garmin IFR avionics. Looking at it always reminds me of something Scotty said in one of the Star Trek movies after he easily and completely disabled the latest and greatest new star ship, "The more they overthink the plumbing, the easier it is to stop up the drain". Those of us who have built the RV-12 as an ELSA are kind of stuck with the plumbing we have.

Moving on . . .

There is a "lighting bus split point" that connects the AV-60000 output in question to all of the panel mounted Garmin avionic devices. But in my case the GTN-650xi did NOT dim so when I get back to the aircraft I'm going to go over all of the setup options and see what is going on. I can see that there is a menu>setup>display item that allows the PFD and MFD backlight to be controlled manually or through the lighting bus or photo cell (three choices). Also going to check the same in the GTN-650. I'm assuming that changing it will prevent the ability to control the brightness of all displays with the one knob on the panel. But, losing the screens in IMC would have been interesting although the autopilot would have continued functioning.

 

[Walt]

Normally if the G3X light bus power goes to 0v the screens revert to using Photo cell.

 

[alcladrv]

Normally if the G3X light bus power goes to 0v the screens revert to using Photo cell.

That's how it works my -7A. With nav lights ON, G3X screens are dimmable through a knob connected to the Vans LC-50 dimmer. With nav lights OFF, the photocell controls.

 

[henrysamson]

Normally if the G3X light bus power goes to 0v the screens revert to using Photo cell.

That would be perfect! Maybe mine is doing this. Is there a user adjustable baseline setting when using the photo cell? I'll be back at the A/C later today and play around with it and see what I find.

 

[Brantel]

That would be perfect! Maybe mine is doing this. Is there a user adjustable baseline setting when using the photo cell? I'll be back at the A/C later today and play around with it and see what I find.

Yes, there is a lighting control curve you can adjust. Check out page 30-148 & 149 in rev AZ of the installation manual. Pay particular attention to the Lighting Bus Off Threshold setting. Your GTN has a similar setup page.

I highly suggest going to the manuals first before just poking around in the settings blindly. These things are complex and its best to understand what the settings and features do before changing them.

 

[lr172]

Normally if the G3X light bus power goes to 0v the screens revert to using Photo cell.

I have the 370 series and you can create a custom curve so that once dimmer input volts get below a certain level it reverts to whatever you want; full bright in my case. 370 doesn't have a photocell. My GRT doesn't have such a feature, so skipped the ext dimmer.

 

[rcarsey]

I experienced this issue during my testing too. I think the issue was that when the fuse blows, the voltage didn't drop to 0.0v. There was just a little phantom voltage (0.1v or so) on the line to make it not think the line was dead. Test it with the engine running, in daylight.

Also, another surprise is if your EFIS fuse blows in flight. You'll lose both your screens (and no, the EFIS Battery: ON switch won't do anything).

 

[BobTurner]

I have the 370 series and you can create a custom curve so that once dimmer input volts get below a certain level it reverts to whatever you want; full bright in my case. 370 doesn't have a photocell. My GRT doesn't have such a feature, so skipped the ext dimmer.

.??My GRT Hx has exactly the same user-defined input matrix mentioned by someone else, above. e.g., 0 volts = full brightness; 0.3 volts= full dim, 3 volts= 30% brightness, 5 volts =brighter, 12 volts=full bright.

 

[subpar_bucker]

So, I guess the dimming circuit has to get power from somewhere and in my RV-12iS it comes through the Nav/Strobe fuse. A few days ago the Nav/Strobe fuse blew and the PDF and MFD screens (Garmin G3x Touch) became so dim that we thought that THEY had lost power or died. It was a sunny day and we could not see anything on the screens. The fuse did light up so we knew the source to the problem fairly quickly and changed the fuse. I repeated the failure in the hangar (by pulling the fuse) where the light level is lower and the screens are functioning but are barely readable. I don't know why the fuse blew. The aircraft had about 15 hours on it at that point so maybe it was just a bad fuse. It happened just as the airplane touched down.

Just putting this out there to see if anyone else has experienced this and has any comments or suggestions. Yes, this is all handled by the AV-60000 module. I'm wondering if there is a way to set the lowest possible brightness level on screens so if this were to happen again they would still be readable.

Henry

This has come up before. If you look at the strobe light documentation it calls for a slightly larger fuse than Van's calls for (5 vs 7.5 IIRC). I made that change and also replaced the left wing connector with what's shown in this SteinAir video:

after I noticed some brightness issues with the strobe on that side. I probably could have fixed the original connector, but the SteinAir solution was more idiot proof (at least given my level of idiotness

 

[henrysamson]

I experienced this issue during my testing too. I think the issue was that when the fuse blows, the voltage didn't drop to 0.0v. There was just a little phantom voltage (0.1v or so) on the line to make it not think the line was dead. Test it with the engine running, in daylight.

Also, another surprise is if your EFIS fuse blows in flight. You'll lose both your screens (and no, the EFIS Battery: ON switch won't do anything).

That is what was happening with mine. I raised the cutover to photo cell voltage to 3 volts and all is well. The lighting bus voltage range is only from 8 volts at the low end to a little over 9 at the high end. I was also able to customize the curve to have a lower brightness with the dimmer knob at its lowest setting and also got rid of the delay in response which was set to 2 seconds. Thanks for all of the help!

So if the EFIS fuse blows you lose the PFD? That is disturbing to say the least. Looking at the wiring diagram I don't see how that can happen. The EFIS battery is connected directly to the aircraft battery and the power output from the backup battery goes directly to the PFD. I'll try pulling the fuse on my aircraft and see what happens. I'll let you know.

 

[FlyingSquirrel]

That is what was happening with mine. I raised the cutover to photo cell voltage to 3 volts and all is well. The lighting bus voltage range is only from 8 volts at the low end to a little over 9 at the high end. I was also able to customize the curve to have a lower brightness with the dimmer knob at its lowest setting and also got rid of the delay in response which was set to 2 seconds. Thanks for all of the help!

So if the EFIS fuse blows you lose the PFD? That is disturbing to say the least. Looking at the wiring diagram I don't see how that can happen. The EFIS battery is connected directly to the aircraft battery and the power output from the backup battery goes directly to the PFD. I'll try pulling the fuse on my aircraft and see what happens. I'll let you know.

The way Vans has the backup battery wired there is no pass through power. If the EFIS battery blows there is still 12v on pin 5 of the IBBS so it doesn't sense a voltage drop and doesnt output power. To get the IBBS to come alive in this situation you would have to turn the master off, as designed...

 

[j4cbo]

I have examined the wiring diagram for the RV-12iS with the Garmin IFR avionics. Looking at it always reminds me of something Scotty said in one of the Star Trek movies after he easily and completely disabled the latest and greatest new star ship, "The more they overthink the plumbing, the easier it is to stop up the drain". Those of us who have built the RV-12 as an ELSA are kind of stuck with the plumbing we have.

During the build yes, but once it’s flying you can rearrange things as you like. I’ve done some significant cleanup to my legacy RV-12 (changing all audio, lighting, and engine monitor wiring to go directly to the appropriate component and bypass the AV-50000A) and I’m planning on removing the box entirely once I get a sufficient supply of round tuits.

 

[lr172]

.??My GRT Hx has exactly the same user-defined input matrix mentioned by someone else, above. e.g., 0 volts = full brightness; 0.3 volts= full dim, 3 volts= 30% brightness, 5 volts =brighter, 12 volts=full bright.

Thanks bob. Will have to look at that again, as i never saw that. Thought i read the manual cover to cover. I had even spoken to them about my concerns and they said power was not required and they only needed a rheostat in line with a grd. Wondering if something was changed in the hxr that i have.

 

[rcarsey]

The way Vans has the backup battery wired there is no pass through power. If the EFIS battery blows there is still 12v on pin 5 of the IBBS so it doesn't sense a voltage drop and doesnt output power. To get the IBBS to come alive in this situation you would have to turn the master off, as designed...

not to creep the thread.. but.. ultimately you have a choice -- do you want a radio and transponder.. or do you want flight instruments and a map. I'd rather have all them.

 

[BobTurner]

Thanks bob. Will have to look at that again, as i never saw that. Thought i read the manual cover to cover. I had even spoken to them about my concerns and they said power was not required and they only needed a rheostat in line with a grd. Wondering if something was changed in the hxr that i have.

See the Set Up manual for the Hx
Push “Set Menu”
Select ‘General’
Select ‘External Dimmer Scale’ (table)
Fill in the table as I described above, with both 0 volts and 12 volts giving full brightness,

 

[lr172]

See the Set Up manual for the Hx
Push “Set Menu”
Select ‘General’
Select ‘External Dimmer Scale’ (table)
Fill in the table as I described above, with both 0 volts and 12 volts giving full brightness,

Thanks! Will have a look.