REQUEST: 14V illumination for RT459A transponder?

[[email protected]]

I have a RT459A transponder which was previously installed in a 28V
aircraft. The
internal illumination works, but is too dim at 14V.

Does anyone have the instructions which specify which (internal)
jumpers need to be moved to strap it so that works with a 14V dimmer?

[[email protected]]

wrote:
>...
> Does anyone have the instructions which specify which (internal)
> jumpers need to be moved to strap it so that works with a 14V dimmer?

HoW about a schematic?

[d.l.anderson]

On 19 Oct 2006 08:12:27 -0700, wrote:

>
wrote:
>>...
>> Does anyone have the instructions which specify which (internal)
>> jumpers need to be moved to strap it so that works with a 14V dimmer?
>
>HoW about a schematic?

Sorry, no schematic. I've been searching too!

Maybe these: eBay items 200036742582, 200035961646, 200027838671

Would anyone have a source for the tray-locking cam nut on the bottom
of the 459A? Mine's missing; somebody must have unscrewed it all the
way.

First, a disclaimer. You're treading in FAA avionics repairman
territory for a certified unit. 'nuf said.

The RT459A is a 14v unit internally, and is connected to a 28 volt
supply through a dropping resistor on the back of the mounting tray.
The resistor is a Dale HG-25, 35Watt 8.2 Ohm 3% power resistor
connected between pins 8 and 23. For 14 volt operation, the resistor
is removed (or jumpered), connecting pins 8 and 23 directly. Power
input is always through pin 22, and system ground is on pins 1 and 2.

Pin 12 on the 23 pin connector is the internal instrument lighting
supply. The bulb in my 28v unit is a midget flange base "CM8-443" and
has a magnifying lens (similar to a penlight bulb) to focus on the
fiber optic array that carries light to the squawk code levers. It
has a little blue silicone "condom" over it to produce blue light.


I pulled the lamp and powered it up at 12v on my benchtop power
supply. It is VERY bright at 12v.
I looked up the bulb in Chicago Miniature Lamp:
http://stevenengineering.com/Tech_Support/PDFs/27INCD.pdf
page 2-59. Now I know why it was so bright... it's a 5 volt bulb!

Is it possible that someone changed the bulb in your 459 and
mistakenly inserted a similar looking bulb of the wrong voltage in its
place?

Here's a Service Letter on installation of the "Reply" light...it is
14v. http://www.sigmatek.com/service_bulletins/100L013.pdf

Sigma Tek is the "owner" of ARC equipment:

"On September 1, 1987, Sigma Tek purchased Aircraft Radio
Corporation (ARC) from Honeywell, Inc. Prior to its purchase by
Honeywell in late 1983, ARC had been a wholly owned subsidiary of
Cessna Aircraft. It is interesting to note that at the time when
general aviation was at its highest, ARC was by far our largest
customer. Through ARC, we service and support nearly all of the
avionics and flight control systems for Cessna Aircraft."

[[email protected]]

d.l.anderson wrote:
....
>
> Would anyone have a source for the tray-locking cam nut on the bottom
> of the 459A? Mine's missing; somebody must have unscrewed it all the
> way.

I have several defunct 359/259s. Email me and I will mail you one.

> First, a disclaimer. You're treading in FAA avionics repairman
> territory for a certified unit. 'nuf said.
>
> The RT459A is a 14v unit internally, and is connected to a 28 volt
> supply through a dropping resistor on the back of the mounting tray.
>...

I am aware of how to operate it on 14V or 28V. However, note 1 on this
reference
http://www.aeroelectric.com/Installation_Data/RT359A_459A_859A.pdf
implies that some internal jumpers must be moved in order to change the
illumination for 28 to 14V. Poking around with an ohm meter suggests
that the illumination lamps inside the unit are in a series/parallel
configuration, so the fact that one of the lamps are intrinsically only
5V is not inconsistant...