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Will Depart in...



New Member needs advice

Started by AAnnillo, October 25, 2020, 05:44:52 am

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First time poster and not sure where to post this.

Am considering building a home cockpit for either a Boeing 727 or a Boeing 737 and haven't decided which yet.

Original parts for the 727 are hard to find, that's for sure.
I was lucky to find some, not many, in ebay searches.

Question...does anyone have any suggestions on how to light up the 5V AC backlighting panels and instruments from a single power source and if so, what power source would you recommend?
I am guessing that resistors would be required but have no idea at this point.   I know that maximum amps need to be considered.

If you can help me out, please let me know.  I'm good with soldering and have basic electronics knowledge and am anxious to learn more.


(In Italian, 'Ant-ny')


October 25, 2020, 09:06:46 am #1 Last Edit: October 25, 2020, 09:08:09 am by jackpilot
Hi Ant-ny 

Panels backlighting is 5V DC (not AC) which means that a simple computer power supply (PSU) will do the job. My MIP and Overhead panels are all using those 5V bulbs and a robust (1000 watts) PSU feeds them with no prob.
Just put all red wires (+5V) together and all black wires (neg)together and here you go. (Yellow wires are 12V)
For just a few panels a 300W PSU will do.
Try and test as long as it is 5V.



Hi Anthony,

Welcome to Cockpit Builders! You've pick the right place to help with your project...

Sounds like you might be more interested in a B727 build, if so PM me your email address and I'll send some pics of something that may really interest you.

| FSX | FDS-MIP OVRHD SYS CARDS FC1| PM | PMDG 737-700 | UTX | GEX | UT7 | ASE | REX2 | AES | TSR | IS | TOPCAT | AvilaSoft EFB | OC CARDS & OVRHD GAUGES| SIMKITS | SW 3D Lights | FS2CREW2010 | FSXPassengers | Flight1 AE | MATROX TH2GO-D | NTHUSIM | 3-Mits EW230Ust Proj |



I would love to see a 727! Do i smell OEM build!!!

Jacks totally right on backlight, go for an old computer PSU. I use a 650W and have 30Amps of 5V!

I used to see alot of 727 parts on ebay, and also much cheaper than 737.

I would go for 727 OEM, X-Plane 11, Teensy LC, Fly J sim 727 model.

Thats a sweet setup!


Hello, all.

According to my Boeing 727 complete wiring guide (4 huge volumes), the panels are powered by 28VAC directly from the Main Bus #2. Power from this bus is then passed through a transformer which distributes it throughout with 5VAC.
There is no mention of DC power anywhere for the panels' backlighting or individual instruments.
Thus, my concern and slight apprehension.


Thank you very much for your generous offer,

I am still in the pre-planning stage and don't know which platform I'll be going with.  I appreciate the input!  Right now, it's more of a matter of "CAN this be done?"

Thank you very much, gentlemen.


(Papa was an AAL B727 Captain for as long as I can remember...he moved to the B757 and then retired.
He passed-away a few years ago and would have been in hog heaven with this project of mine)


Panels are backlit by bulbs.
No polarity.



Makes me wonder why Boeing didn't include that info in their wiring diagram. 

AC vs. DC

It makes a difference.

I've seen some instruments and lighting that's says either AC or DC.

It's not the case in this example.


Boeing will be quite specific about how their hardware is powered, and no-one will deviate from the specifications.

Home builders on the other hand...

Since the illumination is provided by an incandescent bulb we can light it up with AC or DC. As long as you don't supply too much voltage the bulb will be fine. A little bit of maths will tell you why 5Vdc is ok for powering a 5Vac bulb (I'm leaving that as an exercise for the reader).

Basically, if you know what is inside the box you can be pragmatic.


Learned something today   :P
Just out of curiosity, what would be the advantage of using 5VAC in a home cockpit with bulb backlighting (OEM or Repro)?


bernard S

to much grief any 73  series go with a 74   you can thank me later 😉


It is interesting to read all the comments on AC vs. DC for illumination of a 5VDC bulb for backlight illumination.

Keep it simple, and make it simple...

Use a 5VDC power supply for this requirement.   They are inexpensive.  You can purchase a standard PC power supply and wire it so you can use both the 12VDC and the 5VDC.  Both outputs of which will provide plenty of Amperage for your backlight requiremens.  Another approach is to use a 5VDC power supply "brick" .

Mean Well makes a very good, low cost, vairly compact 5VDC power supply in a variety of Amperage ratings.

Keep in mind that such a Sim backlighting setup is going to require a lot of Current (Amps).  In my Sim, I use three (3) 5VDC power supplies:  One is a PC power supply (as described above) for the MIP and Overhead units, and a few misc. needs;  A second PS brick is used for the Boeing 737 TQ that I automated for my Sim; the third PS brick is used for the Pedestal NAV/COMs, etc.

As always, it is good practice to Fuse each Power Supply according to the circuits used, eg. Overhead, etc.  Depending on the application of 5DVC to a particular area of the Sim from a single 5VDC power supply, you may want to have multiple fuses to protect those areas.

Also, the use of connectors from each powersupply makes it easy to service/maintain that part of your Sim.  Very important!  Be sure to use a proper wire size that is large enough to handle the Amperage for each part of the power requirement.

It's always a good idea to draw a system schematic showing how the Power is routed within your Sim.  This applies to Primary 120/220 VAC primary power; and 5VDC and 12VDC power routing.   Keep data (USB, etc.) separate from your power runs.

It's also very important to properly Ground ALL AC power coming into your Sim.  Wires tend to com loose, and you don't want any high voltage electrical shorts within your Sim.

For future maintenance/service considerations, it is a good idea to have easy access to "test points" where you can measure the voltage within your Sim.

These are some basic considerations.  Hope it helps.


P3d v4.5x with Sim-Avionics (two computers), FDS MIP, 3-Optoma HD GT1080HD projection 120 deg. display driven by a single EVGA Nvidia GTX-1080Ti Water Cooled.  6dof Motion Platform using BFF 6dof motion software, driven by a Thanos Servo Controller to 6.2 KW Servos.


October 28, 2020, 05:32:17 am #11 Last Edit: October 28, 2020, 06:29:10 am by AAnnillo
I cannot thank you all enough for taking the time to reply.
I truly appreciate all the input.

To say that this potential project of mine is more than a bit overwhelming and intimidating would be a severe understatement!
Your feedback means a lot to me and I am grateful.

I had already purchased a computer PSU with the intention of using it solely as a bench power supply for a 3.3V, 5V and 12V.  It hadn't occurred to me to use it for OEM panel backlighting and instrument lighting, again because of the AC vs. DC 'issue.'
Not wanting to destroy this valuable OEM collection by using incorrect power is, understandably, a major priority.  Chances are slim-to-none that I'd be able to replace any damaged pieces.

I've successfully dismantled a Collins 329B-8N flight director/attitude indicator (I have 2) and have identified the various pinouts for all 3 plugs, with help from an instrument maintenance and operation manual purchased online.  I've tested the various flags and am happy to report that they are functioning very well.  Their power source?---a hacked cell phone-type charger that has an output of 2V to 24V, variable by means of a potentiometer.  And the output voltage you ask.....DC.   Who knew?
I've also tested lighting for panels and instruments with this same charger so when I read that lighting, etc. requires AC power, I become concerned that continuous use of DC power may be hazardous to the panels' and instruments' health, as well as mine!  I will be tackling how to operate (and later, interface) the various sycnhro/resolvers soon as I'm antsy to see this move it's magic.
Fun stuff here!

For now, my sincerest gratitude to you all.


P.S.  By the way, speaking of the flight director---it specifically says in the manual:  [26VAC]...for some power requirements.
For this, I guarantee you that AC will not be swapped for DC.
Additionally, a 115V(AC) 400Hz single phase power source is required (prolly for the synchro/receiver/servo items).  So, the original question remains:  AC power source recommendations...

bernard S

before you go down this rabbit hole

you are about to enter a world of pain think about this are you rebuilding the plane or making a simulator ?


October 28, 2020, 05:04:20 pm #13 Last Edit: October 28, 2020, 05:15:48 pm by AAnnillo
I have no hesitation in going down rabbit holes if I gain knowledge during the journey and later, pass along my knowledge when asked.

Do you have something constructive to contribute?


Hey Bernard,

Anthony is new and doesn't know about the "Bernard cockpit translator" thing yet, like us regulars do. So, turn it on a bit for him, and once he understands the wealth of knowledge you have, he'll get everything you say.

I've been telling him about getting on the phone with you and how it's much different. Speaking with you is amazing and I hope he gets the chance to do that real soon...

Kind Regards,

| FSX | FDS-MIP OVRHD SYS CARDS FC1| PM | PMDG 737-700 | UTX | GEX | UT7 | ASE | REX2 | AES | TSR | IS | TOPCAT | AvilaSoft EFB | OC CARDS & OVRHD GAUGES| SIMKITS | SW 3D Lights | FS2CREW2010 | FSXPassengers | Flight1 AE | MATROX TH2GO-D | NTHUSIM | 3-Mits EW230Ust Proj |


I just purchased a KGS Electronics SPC-30 static inverter which will arrive next week.

Looks very promising--
+28VDC input @ 16A
115VAC output @ 400Hz, 2.6A
26VAC output @ 2.9A

Let the experimenting commence!


Let the fun begin! Start a new thread with your build and post lots of pictures! :)

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