Airplane Circuit Board Help

[Crash_Test_Pilot]

Some of the newer business jets have electronic window shades. It's a neat concept, but they stop working all the time and the cost to get one replaced is ridiculous. I'm trying to figure out how to repair.

Everything mechanical is pretty simple, but there's a circuit board that I'm worried is failing. I sent off to a circuit board repair company and they said they couldn't repair because, "it appears most of the components are programmed chips which we cannot support."

I've attached a couple of pictures for review. Here's my question - can anyone repair a circuit board with programmed chips (without having the program)?

 

[MaxHeadRoom78]

Typically the processor IC has been locked off after programming, security fuse etc, method depending on make/type .

 

[JimB]

Here's my question - can anyone repair a circuit board with programmed chips (without having the program)?

The quick answer is no, not possible.

Looking at your pictures, the only programmable chip is the big 100 (?) pin device with the two paper labels.

I cannot read the markings on the two 16 pin chips, my best guess is that these and the discrete components are what provide the interface to the window "mechanism" and it is these items which are more likely to be faulty than the big processor chip.

The whole circuit board appears to be sprayed with a clear lacquer to prevent moisture problems, that can be a problem when working on such boards.

Sorry to be so negative.

JimB

 

[alec_t]

can anyone repair a circuit board with programmed chips (without having the program)?

It rather depends on what the fault is. Without knowledge of the program details and without a schematic of the board the best you can probably do is to inspect the board closely for any physical damage/problem (e.g. loose components, poor wiring terminations, bulging electrolytic capacitors, dry joints, signs of overheating).
A DMM might be able to detect a failed semiconductor device with an in-circuit test. An ESR meter could perhaps identify a failing capacitor.

 

[Papabravo]

Go into the business of fixing the problem. Make yourself an LLC, contact the manufacturer of the boards and see if you can get a price on replacement boards as spare parts. That might be beneficial to you and other folks with the same problem. Having working boards is always helpful when debugging the non-functional ones. With a good enough relationship with the manufacturer, you might even be able to send boards back for repair. You could actually be the beneficiary of the sky-high repair prices. If I was 40 years younger, I would have jumped on such an opportunity.

 

[Tony Stewart]

I have no idea what intelligence the human-machine interface has (HMI) but the LCD needs only simple signals to polarize and block the light.

 

[jpanhalt]

I suspect the chemistry is not the same as with LCD's. LCD's depend on polarization. From what I have read, the Gentex material used in aircraft dimmable windows is not based on a change in polarization. It is a chemical gel between the two panes of the window that simply darkens with an applied voltage. The change is quite slow campared to LCD's. It's called an electrochromic fluid. Apparently when the voltage is removed, it lightens again. A brief search did not yield much "real" chemical information on the Gentex product.

Here's a link to the Gentex site: https://www.gentex.com/events/ces2024/dimmable-glass/ Here are two links on electrochromism:

Electrochromism - Wikipedia

en.wikipedia.org

https://www.sciencedirect.com/science/article/abs/pii/S0927024823000910

I find it fascinating as changes in color with chemistry have interested me for a very long time. As for this project, maybe those boards are just tarted up variable voltage supplies. Following on PB's suggestion, if I had a working version, I would simple study its output voltage as a function of the control. Control may be as simple as a digital encoder.

 

[augustinetez]

Self repair of anything electronic on an aircraft is fraught with problems considering all the rules and regulations governing such activities.

All repairs need to be traceable and documented as well as done by certified people - not something you want to get involved in, especially if something goes wrong.

 

[Nigel Goodwin]

Self repair of anything electronic on an aircraft is fraught with problems considering all the rules and regulations governing such activities.

All repairs need to be traceable and documented as well as done by certified people - not something you want to get involved in, especially if something goes wrong.

Yes, a friend of mine had a Cessna until recently (he was unable to bring it to the UK when he moved back here, it would have cost too much) and he was telling me the other week what had to be done to do any work on the plane at all, and how everything had to be seriously documented and traceable.

 

[jpanhalt]

Regulations vary by country. We do not know in which country the TS is located. I have experience in the US and owned various General Aviation airplanes from 1971 through 1990. In the US, what's required by our FAA varies by the type of certification (e.g., GA, Experimental, on-demand charter (Section 135), air carrier, and military). Turbines and max gross weight are also factors. Avionics require additional certifications, as the FCC is also involved. As I recall, PB has extensive experience in avionics. I suspect such dimmable windows are considered part of the airframe, not avionics.

With privately-owned GA, non-turbine, and max gross weight less than 12,000# (including a twin engine), I did almost all of my own airframe and engine work supervised by an experienced mechanic with IA (inspector authorization). A friend rebuilt a crashed Mooney and got it signed off. It's the TS's responsibility to be sure whatever is done is properly supervised and signed off. Modifications can be authorized by getting an STC (supplemental type certificate). STC's are not rare. All but one of my airplanes had at least one STC.

Dimmable windows are relatively new and intriguing. I hope the TS visits again and gives updates.

 

[jpanhalt]

With respect to the chemistry presented in my first post, I was struck immediately with the unusual production of a more colored product upon reduction of a dye precursor, Perhaps, the most common example of that is the reduction of tetrazolium salts to highly colored formazans upon reduction (See: https://en.wikipedia.org/wiki/Formazan ).* With formazans, the added electron facilitates a change in configuration and resonance. With dimmable windows, the added electron facilitates aromatic resonance, which causes darkening. Since there is no change in configuration, it is more easily and rapidly reversible. A loose analogy would be supercapacitors in which the REDOX reaction is easily reversible. One might say, those windows are just big supercapacitors.

*In the usual instance, e.g., methylene blue, oxidation of the precursor (leuco-methylene blue) gives the colored product. That effect has been known for a very long time and has been utilized in dyeing textiles since Egyptian times to make dyes that do not wash out.