Problem with floating center position on receiver.

[eberian]

Hi.
I have strage problem with my FS-TH9x. I'm using er9x with latest build. I've noticed that after turn on th9x pwm on receiver has range moved about 30us. I'm using multiwii and in multiwiiconf channels are normally set to 1500us. When i turn on th9x after about 1h of inactivity monitor shows about 1470us. If i let transmitter turned on for about 10 minutes then center point will move to 1500 smoothly (endpoints are also moving).
Have You got any ideas about that ?

[Kilrah]

The first thing you'd want to check is how your radio's stick potentiometers behave, as unfortunately a relatively high number of 9x's have bad pots.
Go to the DIAG screen and look at the values reported for the sticks. See if they move over time along with the output.

If they don't, it could be a bad crystal which causes CPU clock speed to drift over time, either the radio's own one, or that of the TX module or receiver.

[eberian]

I've check potentiometers and values are same whole time. I think that crystal might be a problem. Fortunately my friend has th9x so i could check other set transmitter/receiver. If problem will exist i'll try to desloder crystal in th9x.
Thanks for advice

[ShowMaster]

Maybe a long shot but how about heating or cooling the crystal and caps to see if it make the drift happen on Que.
SM


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[jhsa]

I would try another RF module and receiver before doing that.. If I remember well, it's not the firstr time people complain about it and I think the problem was in one of them, I'm assuming you are using the stock RF module and receiver of course


João

[eberian]

I've just replaced crystal on mainboard. Nothing has changed. I've tested another set of RF modules and same situation (I'm using original RF modules from fs-th9x). Now i'm thinking about selective heating some parts of mainboard. Maybe i'll find zone where problem is placed. Maybe capacitors are a problem.

[jhsa]

try finding someone with a frsky module for example..

[eberian]

I'll try to find someone with frsky modules. I've just tested my modules on another th9x with stock firmware and they are stable as rock. I think that problem is with generating PPM signal to transmitter.

[eberian]

I think that i find where is the problem. Looks like the temerature drift of RF module. I've just opened working module and the 7805 voltage stabilizer is quiet hot. Few blows of cold air and readings at receiver drops to initial value. Now is the question. It is faluty stabilizer or whole circuit doesn't like high temeratures. Input voltage to RF module is 12V from lipo and it is dropping down to 5V on main stabilizer.

[ShowMaster]

I'll try to find someone with frsky modules. I've just tested my modules on another th9x with stock firmware and they are stable as rock. I think that problem is with generating PPM signal to transmitter.

What tx battery voltage for good th9x?
Same as yours 12v lipo or lower voltage?
Sm


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[eberian]

Normally th9x is powered by 8 AA batteries (1.5Vx8 gives about 12V). I've bought Lipo and it works like a charm except problem with drifts (on battery pack problem also exists but i didn't noticed it earlier).

[ShowMaster]

I see you answered some of my questions while I was composing on my iPod with one finger. I'll post it anyway.
As far as 12 v being to much, it think in this case it is. As a test,
Why not add a few diodes in series with a lipo lead to drop the voltage to 10.5 or so fully charged 3 cell lipo. That should reduce the voltage and heat the module regulator has to deal with.
Frsky I understand uses a switching regulator in its modules. Hopefully that's true?
///////////////////
I ask because the 12v has to be dropped to 5 volts for both the 9x and the module. That 7 volt drop ends up as heat. Heat in the tx case, heat in the module case. Maybe try a lower voltage pack like a life 9.9v to see of the drift stops?
What happens drift wise when you heat the board in the tx module?
Also, does your stock 9x module have the new metal enclosed rf deck in it or the older one with no shielding?
There has been a redesign.
SM



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[eberian]

I have old version of module (2 years old) without any shielding. I have an idea to solve my problem. I'll modify power line to module using switching regulator (i'm thinking at placing this in th9x) to drop down voltage to 7,5V (or even 6V). I've never seen module to th9x that need 12V power source. I hope that will help. Meantime i'll try lower voltage battery and check that problem exist.

[MikeB]

The stock module I opened had a 78M05 pre-regulator (5V) in it. You will need at least 7 volts in to this for it to work properly.

Mike.

[eberian]

I have two ways. One: Use 7808 in the middle, Two: bypass 7805 in module and move stabilisation to th9x (more space = better tolerance for temperature). Unfortunatelly th9x is not giving 6V on connector for module, so maybe i could build it myself