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Does anyone know the resistance range for the cadmium sulfide (CdS) photoresistor in the Bendix/King KN-64 DME unit?

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    $\begingroup$ What's a CdS? Maybe provide a link on a schematic, or something... $\endgroup$
    – kebs
    May 3 '21 at 16:37
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    $\begingroup$ CdS is cadmium sulfide, one of two common types of photoresistor. $\endgroup$
    – stretch
    May 4 '21 at 13:00
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    $\begingroup$ If that can help: CdS LDR have a resistance about 1-10+ MΩ at 0 lx, and 1-100kΩ at 10 lx. Example. Note cadmium use is restricted (RoHS). You would have a better answer on EE.SE $\endgroup$
    – mins
    May 4 '21 at 19:49
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As per the guidance of FreeMan:

*I answered this technical question as an electronics developer. But as A&P certified operator, I strongly advise to not do the process listed here. Since any modifications could endanger the safety and operation of the land systems and the aircraft systems, and any modification made by non certified technician would automatically void not only the warrant but also ban the device of operation and his operation could be cause of procedures marked as illegal and can be prosecuted. To repair an electronics device for active civil operation you must have an "Air Agency Certificate" , (14 CFR) Part 145.

The related method is only posted here is intended as an electronics hobby only, again, its not intended to repair an operations active/production/in use VOR/DME or any other electronics device for designed for aviation. If this is intended to operate in civil active operations, it must be taken to a Repair Station certified or get in touch with the manufacturer.*

Original answer:

Are you trying to adjust the dimming? AFAIR,the photocell is mounted behind the front panel , to the left of the display.
I never get the value, but I suggest 2 options.

a)If you disassemble the unit (at least at the point where you have access to the component) and with a multimeter check the value.

b)since you are trying (I guess) to replace for a working one, take the idea these things comes in a lot of values, so its a bit cumbersome to fetch the right one, but in the other side, this is a resistance so it wont harm the unit if you put one below or higher than the original value.

The only effect is the display is going to be more/less brighter. (tip if you go this way before to solder the cell, test it with a couple of wires, to see the results, and once you are fine to go, solder it).

But avoid totally to make a short, this definitely will damage for sure the unit display.

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    $\begingroup$ These seem like bad things to do unless one is an A&P or otherwise licensed to work on aircraft avionics. $\endgroup$
    – FreeMan
    Jan 14 at 18:00
  • $\begingroup$ Well, thats why Im saying, but the reasons to do this, the outcome and consecuences are not in my knoledge or liability. And @Mark Wylan should abide by the reglaments and laws relative to the support of aircraft electronics systems and its his obbligation to certify the righ operation of the device for the intended use. What and why it does is up Mark Wylan, as avery question and answers posted here. But it's a good warning. Im modyging the answer. Thanks!! $\endgroup$
    – avelardo
    Jan 14 at 19:02
  • $\begingroup$ is up Mark Wylan, as avery question and answers posted here. Errata I mean: is up Mark Wylan, as avery question and answers posted here is related to the user who makes the question. $\endgroup$
    – avelardo
    Jan 14 at 19:24
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According to http://www.flymafc.com/docs/manuals/king-KN62_KN62A_KN64.pdf, The Maximum Sensor Range for the Bendix King KN-64 DME is determined by altitude and ground station output power and sensitivity. Under normal circumstances, the KN-64 DME has a maximum display range of 389 Nautical Miles, as shown below: Bendix King KN-64 DME Range Specifications.

The Change in Accuracy of the KN-64 DME change from .1 Nautical Miles or .14 Nautical Miles from 0 to 99.9 Nautical Miles, as shown below, along with Sensitivity:

Bendix King KN-64 DME Range Accuracy Specifications and Subject Change Calculations.

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    $\begingroup$ Hi @Wasabi - isn't the OP asking for the electrical resistance range - not the "system perofrmance"?? $\endgroup$
    – Mr R
    May 4 '21 at 5:01

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