Devo 8s Found a resistor BURN

More
04 May 2013 18:27 #9552 by junpower
Devo 8s Found a resistor BURN was created by junpower
Hi can some one advise on the burn resistor? The Tx behave as if nothing happen till I lost signal of my plane in short distance. After Checking, i found the resistor was burn.
Attachments:

Please Log in or Create an account to join the conversation.

More
04 May 2013 19:40 #9558 by clearprop88
Replied by clearprop88 on topic Devo 8s Found a resistor BURN
What are you using for power? How many volts?

Please Log in or Create an account to join the conversation.

More
05 May 2013 03:53 #9575 by junpower
Replied by junpower on topic Devo 8s Found a resistor BURN
m running lipo 7.4v.

Please Log in or Create an account to join the conversation.

More
05 May 2013 13:11 #9595 by PhracturedBlue
Replied by PhracturedBlue on topic Devo 8s Found a resistor BURN
That is the power resistor. it is tied to a couple diodes and then a 3.3V regulator. My guess is that at 7.4V you are putting about 3 times as much power through that resistor as it was designed for.
It is a 10 ohm half-watt resistor. for a 7.4V supply I'd probably replace it with a 20ohm 1watt resistor (but you'll probably be stuck with Lipos going forward since that would significantly raise the minimum voltage required to run the Tx). You could also use a 10ohm 2 watt resistor if you want to be able to go back to a 4.8V pack, but you'll be wasting a lot of power as heat.

Please Log in or Create an account to join the conversation.

More
05 May 2013 16:51 #9601 by clearprop88
Replied by clearprop88 on topic Devo 8s Found a resistor BURN
A fully charged 2s Lipo has a voltage of 8.4 V.
I use 2 diodes in series with the lipo battery, that drops the starting voltage to 7.0 V. Still a little high, but I haven't had a problem yet.

Please Log in or Create an account to join the conversation.

More
06 May 2013 21:06 #9630 by richardclli
Replied by richardclli on topic Devo 8s Found a resistor BURN
It is strange that the resistor is burn.....

Devo8S supports 2S LiPo batteries out of the box, Walkera has offical 2S LiPo pack for Devo8S released, so it should not cause any problem.

I used 2S LiPo batteries for Devo8S for some time without any problem. So I do not think the resistor burn is due to 2S power source.

Please Log in or Create an account to join the conversation.

More
06 May 2013 21:18 #9632 by Blayd
Replied by Blayd on topic Devo 8s Found a resistor BURN
I didnt realize Walkera 8S was supported for a 2S lipo?
I just assumed since the stock dry cell set up was only 6v, they wouldnt support anything higher....
I currently run lipo's in my 2801Pro's, with no issues, but the 2801 is 12v stock, 12.6v on a fully charged 3s.
I'm new to the 8S so I've been looking at whats being run as a voltage source other then dry cell or NiCad.

Devo 8S
Trex500ESP
Trex500ESP (Belted tail)
HC500SE
Trex700N2E

Please Log in or Create an account to join the conversation.

More
07 May 2013 01:34 #9636 by clearprop88
Replied by clearprop88 on topic Devo 8s Found a resistor BURN
WOW sells a lipo for use with the Devo 6, and 8. It has the special connectors, so it's a direct plug in. They say it's safe, but I still have my doubts.

Please Log in or Create an account to join the conversation.

More
07 May 2013 07:00 #9651 by junpower
Replied by junpower on topic Devo 8s Found a resistor BURN
I had check the resistor is a 6.8ohm 5%.M not sure also whether those diodes are burn as well.

Please Log in or Create an account to join the conversation.

More
07 May 2013 10:59 #9659 by RandMental
Replied by RandMental on topic Devo 8s Found a resistor BURN
Since we are speculating - I don't have mt 8s close so I cannot trace the circuit, but right next to it on the photo in the first post is an UTC78D06L, which is a linear voltage regulator delivering 6.0V at 500mA max. This I believe is the NiMH charger circuit as the rest of the electronics runs on 3.3V.

Based on the value and size my guess is this resistor either drops the voltage from the external charging connector (should be max 12V) and thus splitting the power dissipation (heat) between the resistor and the 78D06L regulator chip;

OR

It drops the voltage from the battery pack (up to 6V when charging) to lower the power dissipation in the 3.3V LDO. That could explain the RF power drop since it burned, as it would probably now have a higher value.

Please Log in or Create an account to join the conversation.

More
07 May 2013 12:33 #9665 by PhracturedBlue
Replied by PhracturedBlue on topic Devo 8s Found a resistor BURN
Actually mine is a 6.8Ohm as well. I just read what was on the silkscreen (10ohm) and assumed they'd followed it.
The power circuit is a bit odd. I have a full diagram of it somewhere. I think there is something wrong with it as I smoked one of the switching transistors doing nothing more than turning the Tx on/off (the cheap switch failed which somehow led to the transistor burnout). It is also possible that the resistor does get really hot due to the Lipos, but hasn't failed. Did you check it with an ohm-meter (with the batteries removed of course)?
the full voltage also goes directly to the CYRF Module which has its own ldo. Rereading your 1st post it isn't clear if you are having a range issue or if the tx is no longer functional. If it is only a range issue, you probably burnt out the cyrf power-amp. The only way to know is to remove the shield and check it.

Please Log in or Create an account to join the conversation.

More
07 May 2013 17:01 #9678 by junpower
Replied by junpower on topic Devo 8s Found a resistor BURN
Tx still working like normal. I did a test leaving tx in a room and receiver signal cut off around 10m. I had confirm is e Tx problem as i tried new receiver as well. Where is the cyrf power amp ?

Please Log in or Create an account to join the conversation.

More
07 May 2013 17:21 #9680 by RandMental
Replied by RandMental on topic Devo 8s Found a resistor BURN
The amp is inside the Metal can of the TX module. However, first measure the resistor, if it is not around 6.8ohm, replace it. Depending whether it is a metal film or carbon based resistor it resistance could go up when it burns, thus now not allowing sufficient power to go through to the Metal RF unit.

Please Log in or Create an account to join the conversation.

More
08 May 2013 15:50 #9706 by junpower
Replied by junpower on topic Devo 8s Found a resistor BURN
Had change he resistor,is still the same. please advise on how to trace CYRF Module circuit .

Please Log in or Create an account to join the conversation.

More
08 May 2013 16:11 - 08 May 2013 16:11 #9708 by PhracturedBlue
Replied by PhracturedBlue on topic Devo 8s Found a resistor BURN
you'll probably be better off to just buy a new module for $10. fixing the CYRF module will be rather challenging unless you have access to the micro-smt devices or PA parts, and the ability to do fine-pitch qfn soldering.

I don't have a circuit for it, but you can find a documented image here:
openrcforums.com/forum/download/file.php?id=538

Link page is here:
openrcforums.com/forum/viewtopic.php?f=5&t=362
Last edit: 08 May 2013 16:11 by PhracturedBlue.

Please Log in or Create an account to join the conversation.

More
21 Sep 2013 21:56 #13971 by junpower
Replied by junpower on topic Devo 8s Found a resistor BURN
Did eventually bought a new module replace and control distance is a lot better. Over these few month of flight in an open field, I crash as the signal suddenly lost came back. Distance within 1km maybe 700m.
Is there other place in the circuit I should check?

Please Log in or Create an account to join the conversation.

More
22 Sep 2013 04:04 #13976 by sbstnp
Replied by sbstnp on topic Devo 8s Found a resistor BURN
There may be other factors involved, such as protocol, receiver sensitivity, type of antenna used on the receiver and polarization, etc.

For example a DSM2 Orange RX with simple 32mm (actually around 29mm) wire as antenna and ground reflector will get around 600-700m range. You need better antennas and better receiver design to go past this distance.

Not all radio gear is created equal so do not expect same performance from different manufacturers or theory.

Another things is if you read on the internet take it with a grain of salt, and I speak from experience here :)

Devo 10 + 4in1
Spektrum Dx9
FrSky Taranis + TBS Crossfire

Please Log in or Create an account to join the conversation.

Time to create page: 0.060 seconds
Powered by Kunena Forum