Miscellaneous - Converting a Spektrum DX7 from Mode 2 to 1

Oh no! I've bought a DX7 on the wrong mode

You are not alone! I bought mine on Mode 2 and then realised that there's no easy way to get it to function on Mode 1 (see diagram above for the differences in the modes). Apparently it requires a return to base firmware modification, at some cost.

After removing the back of the set and moving the ratchet from the left stick to the right, and vice versa with the return spring I found the only way I could implement 'delta' mixing was to create two custom mixers one mixing 'AIL to THR' and the other mixing 'THR to AIL'. Bear in mind that 'THR' in my case is actually my elevator servo.

The problems with this solution were that I lost Dual Rates on elevator - instead the elevator DR switch gave me throttle dual rate! Furthermore, I had some issues with the failsafe not doing what I wanted. Not good eh?

So what next?

All my web searches amounted to nothing so I decided to grab my soldering iron and see what I could do. Fortunately, it turns out that I could put the soldering iron away and just grab a crosspoint screwdriver instead! This is a non-destructive and completely reversible mod!

Disclaimer: I modded my Tx as I cannot be without it while it's sent away for official remoding. For 'proper' modding, why not send your set back to the source. If you wish to (probably) invalidate your warranty and be frustrated by losing tiny invisible screws then read on! Any damage caused to your Tx following these instructions is your doing.

Note: any screws you take out, please put them somewhere safe - and preferably in separate piles with a note to say where they're from.

Let's get started - remove the backplate

OK, flip the Tx over take out the battery and unplug it, remove all the case screws and then remove the back of the Tx.

You'll find that a single circuit board containing the battery socket is attached to the backplate. It's easier if this is removed so you can get the backplate completely clear. Notice that the orange/grey wire attach to the circuit board where it says 'red/black' - irrelevant but made me chuckle. The single crosspoint screw detaches this PCB.

NOTE - from now on, the pictures will show the sticks labeled as they appear from the front of the set! Also note that, as mentioned, I've already changed the ratchet and spring to my mode.

The mission objective

Our mission is to somehow get the output from the right stick (six white wires with a brown one) over to the opposite side of the board where the left stick (six white wires with an orange one) are plugged in. However, they're not plugged in. The white connector is a soldered joint despite appearances and even if we could successfully unsolder all six at once, would it work? Who knows?

An easier solution would be to swap the Y axis potentiometers, i.e. to make the left stick turn the right potentiometer and vice versa. These are fortunately mounted on symmetrical PCBs and so can be directly swapped.

See diagram below - incidentally, in this diagram I've carefully removed the RF board from the Tx by removing the four black screws holding it in place. Handle this with care and, if you unplug the antenna lead please remember to replace it later!

However - the astute reader will notice that the digital trim switches will be reversed, but you can't have everything right?

Set the wiring free

With a small flat bladed screwdriver you can release the small plastic cable ties that hold the wiring loom together. These ties can be replaced and reused later in the spirit of recycling.

Remove the power switch and fuse PCB

Right in the centre of the Tx is a PCB containing a fuse, and on the reverse side, the power switch. This is held in place by two small black screws and a large shiny one in the middle. Things are easier if you remove this board - shown still in place below.

Now remove the stick gimbals

Each gimbal is held in place by four crosspoint screws. Referring to the photograph below, undo these screws and then gently lift out each stick gimbal. This makes access to the potentiometer boards very easy. The screws holding the gimbals are different from most of those removed so far so please store them separately.

Removing the potentiometer PCB

The potentiometer PCB is held in place by a small metal bar which keeps the pot in contact with the stick mechanism and then directly to the gimbal via a black plastic subframe, attached with two black screws. See photograph below.

Remove the metal plate and then undo the two subframe screws. This allows the PCB to be lifted free of the gimbal. With both sticks removed, simply exchange the PCBs and reattach them on the opposite side, making sure everything moves freely as it should and the microswitches click when you apply the trims, as they should.

Note: Make sure each stick is centred and that the potentiometer is in the 'twelve o'clock' position. This is the pot centralised and can be confirmed by running it through it's travel in both directions to get an idea of the centre.

Routing the wires

With the potentiometers now successfully relocated, the wiring loom - those orange or brown groups of cables - can be rerouted. Cross them over below the power switch PCB as shown below.

Putting it all back together

The question is can you get the thing back together without having screws left over? If so then a job well done. If not then join the club!

Replace all the PCBs and bits you've removed, retie the cable ties and make sure that little antenna lead goes back securely into place on the RF board. Replace the back of the Tx, plug in the battery and then see what happens...

The good news

Your Mode 2 Tx is now Mode 1 - you can use all the pre-programmed mixers, the dual rate switches will now affect the correct functions and the failsafe will throttle back rather than apply up elevator which is what mine used to do. If you have any problems with the failsafe, hold the sticks where you would like them to be should you lose signal and then rebind the receiver (may be specific to the AR6100 and 7000).

The bad news

You will find that the digital trim display on one side seems back to front - it stands to reason since we've inverted the potentiometer PCBs. However, on my Tx this is on the throttle function - where I never ever touch the trims. The elevator trims on mine (left stick) are fine and work in the correct sense.

Finally

I hope this has worked for you and unlocked the features of the DX7 that were previously unavailable. My Tx is now operating as it should have right out of the box. Also, no wires have been cut and nothing resoldered so, should Spektrum ever release details of how the end user can change the firmware to another mode, simply put everything back as was!