May have figured out what killed my plane- DX5 power glitch

[CNY_Dave]

Was testing out the servos etc on my new plane, AR6210 RX with satellite, DX5e, when the plane stopped responding. Walked to the front, peered in the hatch, yellow sig light is out on the RX and the lost-link red LED is flashing that it has lost signal once.

Wiggled the sticks, shook the TX, no idea what's wrong. Did not regain link until I power cycled the TX, then it was solid over multiple powerups on TX and RX.

I recall there was someone who had a problem with the power switch on their DX5 (was too sensitive and they had to mod it to keep it from glitching) so I fiddled with the switch.

Sure enough, a slight pressure off to the side or even down could power cycle the TX by briefly shutting it off.

But, that's not what happened when it lost sig.

Fiddled with the power switch some more, and multiple times I was able to get the TX to stop transmitting, sig led on the RX out, but WITHOUT glitching the LED on the TX and without the TX making its startup beeps!

Holy crap!

Would not resume transmitting until it was power cycled.

Seems as though if you cycle the power fast enough the processor (or something in there) locks up but the reset circuit doesn't catch it and reboot things like during a power cycle.

Also telling was sometimes when momentarily cutting power (faster than you can cycle with the switch off-on) when the RX regained the signal the sig LED would flicker then become solid.

I wonder how many planes have gone down because of this? In addition to my flightstar 40 which crashed due to probable signal loss.

I wonder how many brownouts (with a DX5 TX) were really this issue?

Going to have to find that repair thread and see how to disassemble this thing down to the switch.

[flydiver]

you might want to watch this:
Faulty Spektrum DX5e Radio

[CNY_Dave]

Yeah, that's it, mine's not as sensitive though, and when it happens sig never comes back, as opposed to most cases he showed where sig does come back.

Now I really need to search for that repair thread I dimly recall.

[CNY_Dave]

OK, have read enough to realize knowledge of this issue needs to be more widespread, and also apparently the DX5e has two power switches in parallel for different circuits, one goes to the actual radio stuff and the other to the LEDs/beeper and who knows what else, that's why the TX function can cease with the LEDs on.

I think the easiest fix is to remove the rear panel, bridge the switch connections with wire to 'on', and add a good switch to the battery feed from the battery tray. Will need to put the switch where it can't get jostled, of course.

I don't see a compelling reason to replace the parallel-switch action of the original switch as it does not seem there is a timing issue where one circuit needs to go hot/go dead before the other.

[flydiver]

Why not send it in? Horizon has a good reputation for fixing their stuff.
Their one drawback is they will never admit to actual manufacturing deficiencies or well known problems with their products.

[CNY_Dave]

I am guess they would just put a new switch of the same design in that would eventually cause the same problem.

Much better to actually bypass the crappy component.

Dave

[CNY_Dave]

Opened up my troublesome DX5e yesterday, as some have I also also found the slider did not seem to be allowing the switch to travel all the way to either the 'on' or 'off' positions, the 'off' position might not seem to be a problem but the 'off' contacts seem to be involved in the trainer port, so some of the circuit is different when using it as a buddy box.

Something interesting I saw on the 'off' contacts, I was ohming the critter out and saw a dozen ohms across one pair of the 'off' contacts and 200 on the other pair, after working the switch directly a few times with the slider off this dropped to 1-2 ohms.

I think this shows an important component of the failure, that being full travel of the switch is critical to fully wiping off the oxide buildup on the contacts, probably when you set the switch to off or on the contacts actually travel a bit past their rest position, but when restrained by the slider slot the contacts just bulldoze crud up to bu not past their rest position.

Another aspect I also found is that if the switch was not fully in the 'on' position, the long switch arm restrained from the last bit of travel, the entire switch arm is 'rocked' back a tiny bit (tilted towards the 'off' position), so not only are the contacts not fully in position, but the spring pressure on them is actually reduced because if the arm is cocked, so is the actual slider in the switch. In this condition the degree of contact was very susceptible to very small motions of the switch arm.

So it seems like the problem is a perfect storm of crud buildup and reduced pressure on the contacts and the arm being able to transmit tiny motions right through to the contacts, all due to the slider not letting the switch achieve full travel.

What's funny is the hole in the plastic looks adequate, but the thick plastic decal actually has a slightly smaller hole.

Dave

[HobbyJumper]

At the risk of cross-posting...exactly three of mine, before I gave up on the DX5e and upgraded. Luckily they were smallish foamies and repairable.

Originally Posted by CNY_Dave

Holy crap!

I wonder how many planes have gone down because of this?

[dgjessing]

Well crap - I've got a DX5e on the way...

[CNY_Dave]

Just do a vigorous 'tap test' on the bench once in awhile.

I had to bypass the switch completely, my attempted fix wasn't reliable in a later bench test.