EL Panel removal?

[Rick Erwin]

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

[Rick Erwin]

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

[mshac]

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.

[Kim Geyer]

I replaced one of ours with the max dim from spruce. Cost @ $300.00. It also does away with the transistors

[Rick Erwin]

Originally Posted by Kim Geyer

I replaced one of ours with the max dim from spruce. Cost @ $300.00. It also does away with the transistors

Thanks Kim. Do you recall if the MaxDim you used controlled any EL panels?

Rick

[Rick Erwin]

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

[Rick Erwin]

Originally Posted by mshac

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.

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

[Rick Erwin]

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 top transistor on the transistor panel controls the dimming of the under glare shield flood lights (except for the center flood/registration number light, which is illuminated at full intensity continuously).
• The middle transistor controls (in my case), the center under glare shield flood/registration number light, and the dimming of the instrument panel post lights and integral instrument lighting.
• The bottom transistor controls the post lights on the pedestal.
• Your mileage may vary.

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