It's a long story that I will try to summarize. The latest revision of the magnetometer that had some design improvements including making it easier to manufacture to boost production using the pick and place machine, but that also came with a weird issue. 

When I was developing the APM Oilpan we had some noise issues on the 3.3V line caused by a missing 200K resistor on the Voltage Reference pin on the 5V side of the I2C translator (obviously this board never saw the light), if you don't populate this resistor it will introduce terrible noise on the line and cause the analog sensors to fail, this bug was found by Jose Julio (Thanks!). 


A curious thing is that the first version of the magnetometer didn't have this resistor (it worked fine anyway), in the second revision i tried to do the right thing and follow what the datasheet suggested so I added the 200K resistor (same that caused terrible issues on the Oilpan because we didn't use it), expecting some improvement. 


When the boards arrived from the fab, we assemble some and they appeared to be fine, Cindy (our testing lady) added the observation that the sensors were slightly noisier, but we didn't listen (Sorry Cindy!). For the pressure of months of long waits we just released the boards. In just matter of days we received tons of complains.   


After days trying to solve the problem we finally discover that the 200K was the issue. The 2nd issue we have discovered but is not critical is that the voltage regulator will not perform well if you don't suck enough current from it, the magnetometer uses very, very low power and the best practice to solve this is to add a 200 ohms resistor from the 3.3V to GND to add enough load to it (Thanks to Nathan Siedle for this trick), we are not doing this right now, so you will see a power supply output of 3.7V, but the performance is perfect. 


All new boards have this fix, but for those who already got affected boards I would like to give a sincere apology to all our custumers and I would like to offer two resolutions to this problem:

1.- Send it back and we will repair it for you. We will cover all the shipping expenses. Please contact custumer support for more info: help[@] 


2.-Repair it yourself (DIY) quickly and safely by following the following instructions.


NOTE: Before you repair your board, check if your board has a resistor marked "204". This means it has not been fixed (see the first two photos of the repair steps for reference), and if you see instead a resistor marked "0" your board is fine.

If you choose to repair it yourself and something gets messed up, you cannot then return the board. If you are unwilling to take this risk or are feeling a little uncertain about your soldering ability, do not do this. Just return the board for replacement.






















1- Locate the 200k resistor, it is marked with "204."






















2- With a soldering iron, heat either of the resistor's solder points
and wait a few seconds for the heat to reach both solder points. Weak solder irons may not work very well. 























3- Without applying too much force as no not damage the pads, gently
nudge the resistor with the tip of the soldering iron. 























4-The resistor

should stick to the tip, so just lift the tip off the board to remove
the resistor.






















5- Make sure you the pad are still there. 






















6- To create the solder bridge place the tip of the soldering iron
over both pads and apply enough solder to brigde the pads.














































7- If the solder ball is touching both pads then your are done. 

Views: 2660

Comment by Taylor Cox on January 12, 2011 at 11:28pm
I believe I have the first generation mag, would it be worth it to upgrade or is the one I have good as far as performance goes?

Comment by Jordi Muñoz on January 12, 2011 at 11:41pm
They are virtually the same.. Just smaller. Easier to build for us...
Comment by Ersin Acar on January 13, 2011 at 12:05am
i will try to fix mine, i hope; i wont burn the pcb :S
Comment by Ground Loop on January 13, 2011 at 12:23am

Just to make sure I understood correctly, the rework instructions are to remove the one and only resistor marked "204" and replace it with a short (solder jumper)?

I think I can manage that.


Is there any easy way to test the before & after results?  Is this noise something that would show up in the CLI calibration, or on Configurator?

Comment by Knuckles904 on January 13, 2011 at 12:34am
Glad to see yall got it figured out. Doesnt seem like too bad a fix either. I can vouch for your stores excellent customer service
Comment by sid on January 13, 2011 at 1:57am


             I bought the same from Fahpah , bangkok.. Is it the same board ? I want to use it on Arduquad.. Do I also need to do this ?



Comment by Yogianandh Naidoo on January 13, 2011 at 2:29am

I have a magnetometer from Sparkfun which I wish to use for my Arducopter build. HMC5843. Will I have any issues with this one? It is a very simple looking board compared to the one being discussed here. Does anyone have any advice on this?
Comment by Andrew Dunlop on January 13, 2011 at 2:45am

Many low noise, low dropout linear regulators are unstable with insufficient load, but 200 ohms sounds like rather a lot - over 15mA.  I have usually found 10k to be enough to ensure stability, but then again I do not know which regulator you are using.



Comment by Chandan Roy on January 13, 2011 at 3:17am
I bought the rev 1.1 magnetometer just a month back...And since then I did not fly yet..But I have soldered it to the OilPan and APM and uploaded the AP_COMPASS_TEST code and found that the reading given were fine...
So is there still any need to remove the 200K resistor and bypass it as shown in the tutorial ?..Or if I remove it and bypass then it will work better...

Can someone please explain me...
Comment by sid on January 13, 2011 at 4:29am


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