EL Panel removal?

[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