auto dimming on 540 vs 440

As a data point - I have had the IFD 540 since it was released. I have always had it set for auto dimming. Initially, that worked flawlessly. Around the time of 10.2 release, the dimming became flaky. Sometimes it worked, sometimes it didn't, sometimes it was so dim as to be not usable. Sometimes it changed as I moved the airplane's panel light control (still set on auto dimming). Talked with tech support - got nowhere. For the past several months, it has been mostly working on auto OK. Nothing was changed in my installation - just the 10.2 upgrade.

I've got a new install and mine is quite flakey.

I went to manual mode and noticed a big difference in lighting at a certain point. Here is the video of it below

Edited by wb8wka - 30 Aug 2018 at 4:18pm

Curious sequence of events after selecting auto dim on the ifd 440 in PA28RT201 Arrow IV:

Edited by ChainSaw - 01 Sep 2018 at 9:36pm

ChainSaw wrote: Curious sequence of events after selecting auto dim on the ifd 440 in PA28RT201 Arrow IV: 1. Set auto dim at night ( display was blinding) 2. The very next daylight sortie experienced a burnt out  'radio/NAV light' potentiometer and possibly the transistor on the Piper switch panel (left most thumbwheel). This happened during taxi after turning on the NAV lights which are controlled by a thumbwheel knob that drives a potentiometer that also dims the radio/instrument lights. This would be the potentiometer/ thumbwheel that dim the ifd440 if it is connected and set to dim with the instrument lights. 3. The NAV lights (red and green) on wing tips no longer work. Potentiometer and/or the transistor on the switch panel are clearly blown. Coincidence? Could the ifd 440 display be drawing more current in the daytime than this dimmer switch was ever designed for? Any thoughts are greatly appreciated. Thanks.

Edited by MysticCobra - 02 Sep 2018 at 1:51pm

Mystic Cobra, when your dimmer was burning up three ifds, was the main power to the ifd connected through the dimmer, or was the dimmer connected to some dimmer sensing input on the ifd?  The former would clearly be a problem for a power controlled device since the current draw would be inversely proportion to the voltage, assuming the voltage decreased somehow with tthe dimmer wheel or transistor that is in the Piper switch panels and dimmer circuit. P=V*I.

Edited by ChainSaw - 02 Sep 2018 at 5:44pm

completely agree about not using the ifd or the new parts as expensive fuses. However, we may not have access to ' the good Avionics technician' if you follow my meaning. If the root cause is anything other than worn out parts in the switch panel (pot and transistor) we are in for an expensive episode. We will not be able to troubleshoot back to the ifd or ifd connections/previously known ifd dimmer connections 'do's and dont's' on this issue.

I fried a few IFDs with the dimming circuit in my 182 as well.  Eventually the shop traced it back to a "improperly manufactured pin" but I'm pretty sure they hooked up the dimmer lines backwards because it would work fine for a long time and as soon as I flew at night and used the dimmer, it would fry.

Do avionics techs typically perform the load simulating you described before they connect an ifd? I am sure that my installer did not.  I can't wait to hear what you are posing for  the  'simulated loads' for (7) and(8) in your previous thread. The IFD is likely to be a capacitive load, not purely resistive - characteristic of electrical loads for computers And radio circuits. Capacitive load bank? Heat sinks? Surely you didn't envision a resistor that you would hold with your fingers for this test? Then, put your two simulated load devices across the connections of the Piper switch panel... Don't try this at home or in your airplane.... Please make a reference to a connection diagram for the ifd pins in question.

Edited by ChainSaw - 03 Sep 2018 at 12:31am

Thank you Mystic Cobra. Did any other electrical components, other than the ifds, get damaged during the three episodes you described? For instance, did you have to replace any of the potentiometers or transistors (2 each) in the Piper switch panel when the ifds were blowing due to dimmer connections?

ChainSaw wrote: Do avionics techs typically perform the load simulating you described before they connect an ifd? I am sure that my installer did not.  I can't wait to hear what you are posing for  the  'simulated loads' for (7) and(8) in your previous thread. The IFD is likely to be a capacitive load, not purely resistive - characteristic of electrical loads for computers And radio circuits. Capacitive load bank? Heat sinks? Surely you didn't envision a resistor that you would hold with your fingers for this test? Then, put your two simulated load devices across the connections of the Piper switch panel... Don't try this at home or in your airplane.... Please make a reference to a connection diagram for the ifd pins in question.   Thanks, but no thanks.

No, avionics techs don’t normally do what I described, but then boxes and circuits don’t normally burn up when simply being connected.  In the absence of root cause information, a modicum of caution and analysis is in order prior to just hooking things up.  I’m merely suggesting an alternative approach.  By stepping through 1 to 6, no further action may even be necessary, especially with MysticCobra’s additional insight.  Your only proposal to date was to just hook things up and hope, but that didn’t stop you from being snarky when someone was only trying to help with an alternative approach.  You even made up load scenarios with which to criticize with “Don’t try this at home or in your airplane”.  You don’t have to agree with or accept advice that you receive here on the forum, but if you ask for help don’t bash those who try.

ChainSaw wrote: No worries.  Point being is that installing the simulated electrical  load  in an an aircraft electrical system poses more danger than  ringing out harnesses in the usual manner and connecting the ifd - what most installers do.  The others in this thread describe what installers and users actually experience  in practice. Avidyne units apparently failed safe in these common situations and did not cause electrical system damage or fires, even with the problematic dimmer design described in this thread. Avionics techs/installers, with the  possible exceptionon of Avidyne, are not likely to build a fail safe, simulated electrical load. The  simulated  electrical load was not a good suggestion.

Glad you got it all figured out.  Good luck.

My 540 was installed in early 2015 and I’ve flown infrequently at night since then.

If it matters my aircraft is a 76 A36 Bonanza (14 volt system).

That could be the issue.

Thank you. I’ll give it a try.