Q: troubleshooting 9x m128 green - in flight 'power-on THR check' + low voltage

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nvd07
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Q: troubleshooting 9x m128 green - in flight 'power-on THR check' + low voltage

Post by nvd07 »

Hi all

I had an in-flight issue today, during my third flight, the airplane became unresponsive to my stick inputs, so I raised the Tx over my head, no luck, then shortly afterwards I heard a familiar beep, so I next I looked at the display, it was showing "warning throttle not idle" like at power-on startup and... the plane crashed out of sight... :(

Then I pressed the keys and looked at the display. I noticed the Tx voltage was low 3.4v or so. However Tx sort of operated again though, I was able to use the Rssi info to 'home in' when walking towards the crash location.

I thought one of the cells of the Tx battery had died (it happend to me on a Rx pack) but when I checked them at home both cells were at 4.1 volts !
After turning off the Tx, and turning it back ON, the voltage displayed is normal.

By searching on the openrcforums quickly , I have seen threads about watchdog malfunctions, restarts (but I did not quite understand everything) and that the voltage displayed was going to be half of the true value.
I have also read about removing some caps to the switches/keys input pins, replacing a voltage regulator, troubleshooting the backlight ribbon cable... faulty bandgap devices (mine enabled and is showing 249 at the moment)...
:?: So I am confused.

1) Is there a way to troubleshoot my unit, in order to be sure about the cause ?
Right now i have the Tx sitting at home , turned on , expecting it might replicate what happened this morning. It has been trouble-free for an hour, but I am not doing anything to the switches/keys. Would the test require pushing the keys and dual-rates switches many times until the bug happens ?

2) Also, I had kept the Tx ON continuously for about 40 minutes - is it a bad idea, would it be better to turn it off then on, between flights ?

3) Or was I asking for trouble by running firmware er9x-128.hex anyway instead of er9x-128Green.hex , and should I replace it before the next flights ?

4) Can anyone comment whether the m128green becomes totally free of the watchdog issues after flashing it with er9x-128Green.hex ?
I am asking this because with today's crash this time the plane can still be fixed (several hours of balsa work) but if similar stuff could still happen again (even if it is less often), I do not want to run the risk, because I might not be so lucky another time ... so I would consider using my m64 instead - ( or upgrading to a Radiomaster TX16S sooner than planned ... ).

Thanks

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MikeB
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Re: Q: troubleshooting 9x m128 green - in flight 'power-on THR check' + low voltage

Post by MikeB »

You clearly had a restart/reboot.
If a reboot is caused by the watchdog, the the normal startup checks (e.g. throttle position) are skipped.

Where you using any trim switches when the problem occurred? There has been a problem with the horizon trim switches as they use the analog ground and have been known to cause a reboot (not watchdog).

There is a hardware fix somwhere on this forum for the trim switches.

The "green" version of the firmware should fix the watchdog problem, but I don't have a "green" tx so cannot test it.

Mike
erskyTx/er9x developer
The difficult we do immediately,
The impossible takes a little longer!
nvd07
Posts: 63
Joined: Sat Aug 15, 2020 8:45 am
Country: France

Re: Q: troubleshooting 9x m128 green - in flight 'power-on THR check' + low voltage

Post by nvd07 »

Thanks for your help Mike,

I was not using any of the trim buttons during these flights. However since your are mentionning it, I read about this 9x hardware issue ( https://openrcforums.com/forum/viewtopi ... 120#p69475 ). Out of curiosity this afternoon, I tried anyway, I pushed the horizontal trims several times but they do not seem to disturb anything at all.

As the watchdog reboot is ruled out as well ( because I heard/saw the throttle check message ) , it has to be yet something else...

Would a bandgap malfunction be possible ( mine seems to stay put but I read in the PDF help that they sometimes could vary rapidly... ) ? and if it went bad, could it trigger a full reboot ?
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MikeB
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Re: Q: troubleshooting 9x m128 green - in flight 'power-on THR check' + low voltage

Post by MikeB »

The bandgap is only used to measure the battery voltage, this won't cause a reboot.
A short loss of power might cause what you describe. I suggest checking the battery connections and the power switch. Try waggling the the wires from the battery, check the battery connector is fully pushed in, and try moving the power switch sideways. Also check the 12-way connector and 6-way connector are fully plugged in to the main board.

Mike
erskyTx/er9x developer
The difficult we do immediately,
The impossible takes a little longer!
nvd07
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Joined: Sat Aug 15, 2020 8:45 am
Country: France

Re: Q: troubleshooting 9x m128 green - in flight 'power-on THR check' + low voltage

Post by nvd07 »

Ok - I will not change anything to the bandgap .

In the coming days I will test and investigate the connectors and other areas as you explained. Thanks.

nvd07
Posts: 63
Joined: Sat Aug 15, 2020 8:45 am
Country: France

Re: Q: troubleshooting 9x m128 green - in flight 'power-on THR check' + low voltage

Post by nvd07 »

So i tried to pull on the battery connector and of course by pulling hard enough I ended up disconnecting it and could produce some reboots but not really what happened in flight.

At some point though, by appplying lower amounts of force, possibly on the lower right corner of the plastic case of the Tx, I produced a 'wonky reboot':

Even though throttle was at zero I got the warning message; next, an incorrect voltage, then none of the analog inputs (sticks) were responsive. The discrete inputs however ( navigation keys and timer countdown reset toggle switch...) were all working fine fine. The poor m128 microcontroller was probably very confused!
In order to regain control of the channels the only way out of this was to power OFF the unit via the master switch then ON again, for a clean reboot... No regrets then, there's no way the pilot (me!) could have regained control of the plane in the required amount of time!

I cannot rule out that the plastic case of the Tx is applying some mechanical stress, bending or warping , to the main board, so I'll try again until I can pinpoint the source more accurately.
Here are some pics, to entertain everyone and to free some space on my smartphone ...
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IMG_20210906_002715.jpg (54.01 KiB) Viewed 3694 times
IMG_20210906_002822.jpg
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IMG_20210906_003008.jpg
(110.1 KiB) Not downloaded yet

EDIT/UPDATE: I installed a new connector to the battery leads and flew for several months with no issues. However yesterday (june 2022) while in flight , I experienced another reboot, except this time it was caused by applying some left aileron trim several times. Then I read here on the forum that the schematics had some issues with the horizontal trims being wrongly connected to analog ground instead of digital ground, and the posts about the capacitors and needing to add current-limit resistors to their discharge paths. However, I could not replicate the trim problem back at home. So even if I would apply a fix, I could not be 100% confident in the hardware. Hanging on to my 9x might cause crashes to my remaining airframes... So it is time for me to move to new hardware, and I ordered a MasterRadio TX16s MK II ( and because of possible 'infant mortality' I will let it run on the bench a few days ;) ... then I will be able to fly again ).

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