Cessna 182P Electroluminescent Controller Parts Identification

[tmandell]

Its a long story, but I am helping my father in law repair the interior electroluminescent panel lighting system in his Cessna 182P.  The airplane was built in 1973, so the electronics are fairly straightforward but we are having trouble identifying two items that need to be replaced as they have blown. 

We have be unsuccessful in locating a complete replacement circuit board, even the one we bought from Cessna directly is a bare unpopulated circuit board.  Therefore I am hoping that the community here can help identify the two unknown components. 

I have attached photos of the components in question, as well as the complete electrical schematic for the plane.  Please see page 11.9.2.0 for the electroluminescent controller drawing. 

Thanks for your help

 Cessna 182 Wiring Schematic Dwgs.pdf (2159.02 kB - downloaded 136 times.)

[fzabkar]

The can is a common regulator:

MC1723CG:
http://www.elektronikjk.pl/elementy_czynne/IC/MC1723G.pdf

The other semi is probably an NPN pass transistor. Unfortunately the part number is not visible in your photos (do you have any electronics knowledge?).

BTW, for those who are having trouble seeing the page number in the diagrams, it's page 32 of the PDF.

[floobydust]

The board is a linear voltage regulator that has damage- a glass diode is broken and overall the board shows signs of cooking and running hot.
We could figure it out with full pics of the back and top side.

But I'm confused about where this board is - the three EL panels should have a small HV inverter to power them. Is this [4] Power Supply? This board has lots of extra wires and no white wires.

[Andreas]

Hello

I read the colours of the diode as
Yellow = 4
Blue = 6
Red = 2
Brown = 1

so it should be a 1N4621 diode = 3.6V zener.

with best regards

Andreas

[tmandell]

Hello

I read the colours of the diode as
Yellow = 4
Blue = 6
Red = 2
Brown = 1

so it should be a 1N4621 diode = 3.6V zener.

with best regards

Andreas

Andreas

Thanks very much for the help.  I thought it could be a diode, but I have not done much electronics work since college 12 years ago. 

As others have requested I have also attached some additional pictures of the board, and other components. 

Here is both sides of the bad board. 

The new board from Cessna

The lighting panels that need to be controlled. 

Heat sink, not sure exactly where this fits in, but my father in law asked me to post it up here in case it helps. 

The power supply, note this is also going to be replaced. 

[jpanhalt]

If you have problems finding the MC1723, a suitable electronic substitute might be an xx723, e.g., UA723 from TI.  Getting a 10-pin version in that package might be difficult.

[fzabkar]

If you don't mind paying their inflated prices (US$7), a trustworthy equivalent for the MC1723CG would be the NTE923:

http://www.nteinc.com/specs/900to999/pdf/nte923.pdf
http://dilp.netcomponents.com/cgi-bin/nteinc.asp?partnumber1=NTE923


Edit:

AFAICT, D1 is connected between Vin (via D2) and Ground. IIUC, Vin (INPUT) is 28V, so that would mean that D1 cannot be a 3.6V zener. Its function must be overvoltage protection, whereas D2 provides reverse voltage protection.

FWIW, a 1N4121 is a 33V zener. That would make more sense in that position.

https://www.microsemi.com/document-portal/doc_download/129734-lds-0245-2-datasheet

[floobydust]

For my Sunday crossword puzzle, I drew a schematic of the board to understand it. Please review, I could not see all the parts (big transistor, grey caps) and wires.
It doesn't fit into the aircraft's wiring diagrams. Those show a dual-channel rheostat dimmer with a couple buffer transistors, there are no blue or grey wires etc.
This board seems to be something else, only one potentiometer input from somewhere for "output high" and an always fixed "output low".

The board looks damaged from a power surge (D1 cracked) and could not cook transistor Q4 by itself. Its output was surely overloaded. Strange the board is burnt and discoloured but the power transistor looks fine, it may have been repaired before.

I would first bench test the inverter. Just connect it to an EL panel and supply (small fuse) say 8-10V and see if it works. It might be too bright with only one panel as a load.
A shorted inverter or EL panel needs to be ruled out. The bench should be insulated (wood) or something, as the inverter is high voltage say 100VAC at low current enough to bite. Just using some alligator clips is how I would do it.

Fixing the board, we could recommend part numbers but I think it would just cook again.

[james_s]

This is interesting stuff, I've always been fascinated with aircraft but have not had much exposure to them other than riding on commercial airliners now and then. Always wished I knew someone with a small plane.

While the hardware is fairly trivial and it's only panel illumination, what are the rules as far as tinkering with this stuff yourself or making modifications? Modern EL inverters are readily available, as are EL panels, you might pick up a set to use for testing the stuff you're working on.

[fzabkar]

A friend asked me to repair the controller for the landing lights on his private plane. He had sent it to an authorised repairer and was charged AU$700. When he reinstalled it, he was was faced with the same no-go situation.

I powered up the controller on my bench and was not able to reproduce the fault. However, I was shocked to see the bodgy repair. It looked like some ham fisted gorilla had attacked the device with his soldering gun. The actual fault was a short in the electrical wiring at one of the lights on the wing.

Anyway, the experience left me shaking my head. It makes me wonder about the so-called aviation standards and whether anybody actually oversees and enforces them.

[tmandell]

Thanks everyone for the excellent help. 

The rules around fixing this are extensive, no upgrades are allowed it must be fixed back to factory specs.  Additionally all repairs are being supervised and approved by a licensed aircraft mechanic.  I suspect there have been many issues over the years, I also believe the cause of all the problems is someone at some point drilled through the electroluminescent panel to mount a switch, therefore shorting it out and overloading the controller.  Also prices of components and repairs are several orders of magnitude higher then you would expect. The only replacement electroluminescent panel we could find was $600 USD. Total repair will likely be over 3k. 

Can anyone provide advice on 3.7V or 33v for the zener diode?  The airplane normally operates on 12VDC. 

Thanks again

[fzabkar]

The zener voltage needs to be higher than the allowable operating range of the alternator. A 3.6V zener would be instantly destroyed by a 12V battery.

[floobydust]

The diode D1 is best as a TVS, LM723 max is 40V so something that clamps below that, like P6KE27A is suitable. Check D2 is OK as well.

I think the IC (Q3) is dead because R8 (1R) looks roasted. I would remove R8 and diode-test the IC at pins 1-10 to see if the transistor E-B junction inside is blown open. The other power transistors Q4 I would test as well.

You can bench test the board if you connect a say 10k ohm potentiometer to the "R5"  three wires and see if the output is adjustable.

[tkamiya]

Position of D1 and it being zener diode makes no sense.  A zener will conduct at specified voltage.  There has to be a series drop down resistor before it or it will fry every time.  In order for this to work, what you labeled as D2 will have to be a resistor.

[Andreas]

The rules around fixing this are extensive, no upgrades are allowed it must be fixed back to factory specs. 
Can anyone provide advice on 3.7V or 33v for the zener diode?  The airplane normally operates on 12VDC. 

Hello,

obviously it cannot be a 3.6V zener from the re-constructed schematic.

So either I have mis-interpreted the colours on the photo - or this diode has a unusual coding (is no JEDEC type).
A 1N4121 would have colour coding yellow, brown, red, brown.
I would try to get a parts list exactly for the empty PCB that you got. (to stay in factory specs).

with best regards

Andreas

[floobydust]

I didn't find anything on an archeological dig for the diode part number. The 1N prefix assumption seems to be wrong, it's not a 1N462A, or 1N46xx as these are piddly 0.5W or under 12V which are no good for the application, even a 1W part could not cut the mustard.
Modern TVS diodes are superior to oldies from the late 1960's through mid 1970's, so I would have no qualms using one. We know it's to protect the IC's and everything downstream from transients, although a tiny part by modern aircraft standards, much bigger parts are used today.

What size is the circuit breaker that powers this board? It looks like a design for 1A max based on D2.

[james_s]

Thanks everyone for the excellent help. 

The rules around fixing this are extensive, no upgrades are allowed it must be fixed back to factory specs.  Additionally all repairs are being supervised and approved by a licensed aircraft mechanic.  I suspect there have been many issues over the years, I also believe the cause of all the problems is someone at some point drilled through the electroluminescent panel to mount a switch, therefore shorting it out and overloading the controller.  Also prices of components and repairs are several orders of magnitude higher then you would expect. The only replacement electroluminescent panel we could find was $600 USD. Total repair will likely be over 3k. 

Ouch! That'll do it 

It's too bad you can't even replace the electroluminescent panel with something generic. You could get a suitable strip that would do the job and look indistinguishable from a factory original for under $20 but I figured rules would be an issue on a certified aircraft.

Having to have the repairs supervised by an aircraft mechanic who likely knows very little about electronics reminds me a lot of when I worked for a ISO9001 company, the layman would assume certification like ISO9001 is to make sure everything is done properly, but in reality it pretty much just means that you documented everything you planned to do then did everything you documented, whether the plan makes any sense or adequately ensures quality or safety is easily overlooked. I understand why aviation is regulated to the extent that it is, but it sure would be nice if there was a streamlined way of getting often superior modern electronics approved to replace stuff like this that is not going to cause the plane to drop out of the sky if it fails.

[fzabkar]

The -2 version of this PCB seems to be designed for 28V systems. Can we assume that the -1 version also needs to be rated for 28V use?

1270712-2 Cessna P210 Dual Voltage Regulator Board (28V):
https://aircraftpartsandsalvage.com/aircraft-parts/airframe/electrical-and-lighting/general-electrical/cessna-p210-dual-voltage-regulator-board-28v-2/

[jpanhalt]

Thanks everyone for the excellent help. 

The rules around fixing this are extensive, no upgrades are allowed it must be fixed back to factory specs. 

My experience is limited to the US.  An owner here is/was allowed a fair bit of leeway in servicing his own airplane.  Over more than 20 years, I owned several GA airplanes.  At the time, our law allowed an owner operator to work under the supervision of a licensed mechanic or IA.   After my first year of ownership, I learned what incompetent clowns some mechanics are.  For example, a friend had to make an emergency landing for smoke in the cabin.  A mechanic had left his flashlight on top of the engine. After that first year, I did a lot of stuff myself (including I inspected the inspector) and my supervisor later approved it.  Of course, there was a good deal of trust involved.  I had a pretty close relationship with multiple IA's over the years.  The ones I worked with were typically older, loved airplanes as much as I did, and were independent -- not just hired 9 to 5'ers.

Helping your father fix his airplane is not much different. FAA 337 form is for major repair or alteration.  In my case, almost everything was just a logbook entry by the IA who I worked with regularly.  A 337 is not that complex to do either.  Does your father use it for commercial purposes, e.g., 135 charter?  That might make a difference.

It sounds like some incompetent, ham-handed mechanic ruined the lighting in your father's Cessna.  Does your father know who that was?  Is this airplane new to him?  Can the previous owner identify that mechanic?  I suspect that lighting might be on the MEL for night and/or IFR flight.  So, it needs to be repaired or replaced with a suitable substitute.  The FAA will be of no help in policing work by that mechanic.  A letter and photographs might help, but doing that would also document a non-airworthy condition -- meaning your father might need to get a ferry permit to fly to a repair station.  The closest I came to such a thing was damage to the nose gear done by an FBO in towing one of my airplanes.  That was handled with a phone call and an in-person visit.  The FBO bought the replacement part, and my mechanic and I installed it.

If your father can identify the culprit, than try the direct approach.  If/when that fails, I would consider just fixing it, not talking about it, and getting an annual inspection.  Unless, of course, your father has a similar relationship as I had with those IA(s).  If not, it is time to find one.

[floobydust]

The stock electrical system looks quite noisy, and depending on the upgrades etc. the transient overvoltages on the 12V bus could overwhelm the diode and it shorts and smokes. That's why I ask what the circuit breaker feeding this is rated at- but it didn't give coverage for a shorted EL panel. The whole board is limited by the other diode D2 to draw at most an amp.

Diode D1 for transient protection is not so great by any modern standards, because it is small.
I suggested a 600W TVS as that's all that would fit.  The original alternator regulator is a mechanical Cessna C611001-0101 (by Ford), hopefully replaced by an electronic one. That gives much better power quality, less transients. Modern alternators clamp to around 40V (because their rectifiers are zener diodes) but in the 60's and 70's they did not.
Does that make sense? You don't want this part absorbing transients for the entire aircraft, or it will just fail.

There are also some capacitors on the 12V bus that would need to test OK - 4uF 100V capacitor (0770038-2 pg6 item3) and addition of a 500uF 50V capacitor (old TVA-1315 pg6/7 item15). Ultralights are adding big 10,000uF 50V capacitors on 12V power to suppress noise for the radio and electronics.

The 28V board (1270712-2) is slightly different - no trimpots, two extra wires, extra diodes and much smaller heatsinks.

[fzabkar]

The pass transistors would dissipate a lot more power at 28V than at 14V. Therefore it makes no sense for a 28V version of the PCB to have smaller heatsinks than a 14V version. :-?

[floobydust]

We don't know if the EL inverter got better (efficiency) or the EL panels are the same size (area) as on other aircraft models.
OP's inverter is quite big, it would be a low frequency iron-core transformer beast with low RFI. EL runs off 90-120VAC at ~100Hz I believe.
EL wire is popular for cars, bicycles, t-shirts etc. and you could use a cheap EL wire inverter for testing the panels.
It looks like a shorted EL panel -> overloads inverter -> overloads controller -> smoke. Something like that is hard to troubleshoot without going broke, so I'd split it up for testing.

[jpanhalt]

Here's another option to consider: https://www.aopa.org/news-and-media/all-news/2018/october/09/aircraft-maintenance-electroluminescent-panel-repair

While Beechcraft specific, maybe the same or other stations can service Cessna EL.