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  #1  
Unread 06-10-21, 03:13 PM
Rick Erwin Rick Erwin is offline
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EL Panel removal?

Anyone know how to remove the electroluminescent panel that the pilot’s yoke extends through?

I need to replace the Instrument Panel Lights/Flood Lights rheostat and I can’t find any information on its removal in the parts or service manuals.

There are no visible screws on the face of the panel and with the mass of wires and equipment behind the panel I can’t see anything there either.

I’ve removed the knobs from the front of the panel, but the panel is not any more loose than when they were attached.

Any knowledge on this would be greatly appreciated.

Rick
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Unread 06-10-21, 08:31 PM
Rick Erwin Rick Erwin is offline
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With the assistance of my excellent IA, we got the electroluminescent panel and the rheostat removed.

For posterity’s sake here are the steps.

Extricate the knobs from their posts and remove the nuts securing the switches on the EL panel.

Remove the row of flight instruments just above the EL panel.

With someone inside the plane and someone in the left avionics bay, remove all the switches from the panel as they extend through the EL panel into the metal panel that’s behind the EL panel. There are plastic spring clips on the top and the bottom of each switch that must be depressed to free the switch housing from the two panels. We were able to use a plastic double edge razor blade (the orange ones from Amazon) to wedge between the plastic switch frame and the EL panel to depress the clips to extricate the switches from the EL panel.

Since it would be a living nightmare to lose track of what switches and wires go where ...

Before removing ANY wires from the backs of the switches:
1. Enumerate all the switches with labels, (Klein makes a small book of wire labels, it's available on Amazon.)
2. Zip-tie all wires going to that switch into a bundle to keep them together,
3. Enumerate each bundle with the same number as the switch to which it is attached,
3. Enumerate each wire on the back of each switch with labels,
4. Write down on a sheet of paper which wire label numbers, go in which connection positions, on each switch (Switch #1, Bundle #1. Wire #6 upper-outboard, Wire #3 middle-inboard, etc.)

Once all the switches have been removed, the EL panel will be free from the panel.

To get the EL switch panel out of the airplane, you'll still have to remove the control yoke. If you have electric trim, autopilot disconnect, and trim interrupt switches on your yoke, you'll have to cut the wires running through the yoke shaft. Make sure you enumerate the wires on BOTH sides of the cut, BEFORE you actually cut the wires. You might consider wiring in a "small" barrel cannon plug that will fit inside the yoke shaft so that you will not ever have to deal with that again.

We had to clip a few zip-ties to give enough slack to get the EL panel away from the instrument panel to gain access to the two screws that secure the lighting rheostat to the metal panel.

The rheostat is in a housing that is about 3-4 inches long as this is the rheostat that pushes and pulls to control the under-glareshield floods as well as the panel post lights. The actual rheostat is part number S1904-4. Cessna asks about $900 for the whole unit, and about $350 for just the rheostat. I found the rheostat at Sky Airparts for about $185.

I heard from a friend who said his EL panel had two holes in it to remove the two screws that secure the rheostat, so … some may not have to go through what I’ve described above, unless you still want to remove the EL panels.

Rick
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Last edited by Rick Erwin : 12-16-21 at 10:11 AM. Reason: Additional info on removal of panel switches
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  #3  
Unread 06-10-21, 09:07 PM
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mshac mshac is offline
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Hope you don't mind me jumping in here on your thread.

My EL panel lights sometimes go off and on randomly. I noticed an entry in the airframe log a few years back that mentioned "Repaired panel backlight ground connection."

Questions:
1. Where is the EL panel lighting ground connection?
2. Could the rheostat cause the lights to go off and on?

Thanks in advance if anyone can enlighten me.
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Unread 06-10-21, 10:07 PM
Kim Geyer Kim Geyer is offline
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I replaced one of ours with the max dim from spruce. Cost @ $300.00. It also does away with the transistors
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Unread 06-11-21, 10:51 AM
Rick Erwin Rick Erwin is offline
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Hi Mark,

Since the EL panels run on AC voltage, I don’t think they have a ground per se’.

The EL panels get their power from an inverter that is located directly behind the top of the throttle pedestal. The inverter gets its power via the red wire from the Instr/Map/Radio/Sw Panel circuit breaker through one of the three transistors that are located in the top right side of the avionics bay. The Switch Panel Light rheostat controls that transistor for lighting intensity. The black wire out of the inverter goes to the two EL panels.

I understand the inverter outputs 110 volts AC, but I’ve not been able to verify that. The mounting bracket of the inverter is grounded to the airframe. I don’t know a lot about AC electricity, but I think it has to have a return path back to the inverter, in this case I think the airframe is that return path. Each of the two EL panels have two small gauge wires that connect them to the AC power source.

I’ve seen rheostats that have had “bad spots” in them that would kill the lights. Sometimes exercising the rheostat will clean off corrosion on the windings and allow electricity to flow again, but other times I’ve just had to replace the rheostat.

You might check your transistors to see if you have a bad one, or two, or three. One of mine was dead and the other two came in at 4 and 5 mega ohms.

I’m sure there are some EE kind of folks here, so … where I’m mistaken, please correct me.

Rick
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Last edited by Rick Erwin : 06-11-21 at 11:38 AM. Reason: To check transistors
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Unread 06-11-21, 11:21 AM
Rick Erwin Rick Erwin is offline
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Here are some things I found while researching this system.

There is not any information in the service manual discussing this system, that I could find. Service manual pp 18-74, Plate H16 is the schematic plate I used.

The three transistors that control cockpit light dimming are common 2N3055 transistors, about a dollar apiece. (Some earlier 337’s may have two transistors.)

To test a transistor, find a schematic for the transistor on the web and connect a multi-meter: red to the collector (the collector is the outside of the case of the transistor), black to the emitter pin and a jumper cable from the collector to the base pin. Resistance readings of 12-15 mega ohms seemed to be usual for the 17 2N3055 transistors I tested. I discarded those resistors with less than 10 mega ohms.

The inverter is termed an “Inverta-Pak” and has Cessna part number C613001-0101 made by Astronics with manufacturers part number 71254-6, or Scott Aviation number 804134-01. Cessna 310 model P,Q & R have this part as number 9910047-1, Piper PA-46 has it as number 9910039-1. Cessna 210 L & N also use it.

Rick
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Unread 06-11-21, 11:28 AM
Rick Erwin Rick Erwin is offline
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Thanks Kim. Do you recall if the MaxDim you used controlled any EL panels?

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Unread 06-15-21, 04:38 PM
Rick Erwin Rick Erwin is offline
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Has anyone here ever successfully tested one of your EL panels by connecting the two small gauge wires coming out of the back of the panel directly to 120V AC line voltage from the electrical grid?

Rick
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  #9  
Unread 06-15-21, 11:00 PM
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The Invert-Pak is out on my airplane; all three EI panels went out simultaneously, so following the maintenance manual, the shop is replacing the "Pak." I have part #71254-6 in hand to replace it but cannot find the inverter up under the panel.

With your EI panel out, Rick, would you see if you can locate it?
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  #10  
Unread 06-15-21, 11:24 PM
Rick Erwin Rick Erwin is offline
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Yeah, that’s the same one I have also.

For the location on my plane, read my message to Mark below.

I’m now trying to determine how to test the inverter. I replaced it with a new one but I still can’t read 120 volts out of it. I’m may not be hooking the meter up correctly, or I might have two bad inverters.

Rick
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Unread 06-15-21, 11:34 PM
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Thanks, Rick. Got it... "directly behind the top of the throttle pedestal." I'm leaving a week-long trip in the airplane, and I will, along with my mechanic, get into this when I return. I sure appreciate your post, very timely.
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  #12  
Unread 06-15-21, 11:36 PM
Rick Erwin Rick Erwin is offline
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You’re very welcome, good luck with your repair.

Let me know it it works our for you as I’m still fighting mine…

Rick
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  #13  
Unread 07-02-21, 12:19 PM
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Rick,
According to Cessna Pilot's Association Mag (Vol 16, No 12, December 1999), in an article by Steve Ells titled Cessna's Transistorized Instrument Lighting Systems, he writes: "EL panels can be tested for operation by plugging the leads to a 110V AC wall socket."

For those of us trying to repair transistorized lighting:
1) CPA Article above
2) CPA Article (Vol 19, No 1, Jan 2002) by Mike Busch titled: Lights...Rheostats...Transistors
3) Cessna Service Information Letter SE84-19 titled: Instrument Light Dimming Circuit Troubleshooting
--in SE84-19, Cessna recommends against 2N3055 transistors, and instead using 2N6576 transistors since they have higher gain thresholds.

Inverta-Paks are available from Cessna at $900 or so, or often found on ebay in untested used conditions.

If you choose to completely rip out the existing lighting system wiring and start fresh, Seaton Engineering makes MicroDim solid state controllers that can run all three circuits (EL Panel, Flood lighting, and post lighting) without the need for the heat-sink and transistors and existing rheostats. Still need the darn inverta-pak, though. After fussing with my lighting for 3 months...I think I'll order some miniDim controllers (1 dual, 1 single) and remove the heat sink and run new wiring to the floods, the EL panels, and the posts. If it works as advertised, that'll be the end of the lighting woes.
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Unread 07-02-21, 07:41 PM
Rick Erwin Rick Erwin is offline
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LearJetter, thank you for the info.

Interesting info about the transistors and the rheostats.

I had ordered a used inverter and it was DOA, so I was refunded the purchase price. The next inverter I received worked and served to highlight that the two EL panels needed some love. The switch panel one is intermittent, and the flaps panel has a strip down the middle that is dead.

I'll be sending both of them off tomorrow to be repaired. I hope this takes care of my problems with this system and that your problems are solved soon also.

Rick
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Unread 07-03-21, 12:58 PM
wslade2 wslade2 is offline
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What about repair of EL panel. Mine are cracking and surface peeling, let alone working.
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