Monday, December 8, 2014

Repairing GPS & Compass Modules and Cables

I cleaned away black tarnish and corrosion from pins of PicoBlade socket on the BS-126 GPS-Module (HK Nova stock one). The blade-pins appeared to be made from a solid/non-plated metal. Tarnish and pitting (causing the poor electrical connection) was pretty deep and hard to remove, but I managed. I carefully scraped with a small/dull hobby-razor knife, used a special file for cleaning/ burnishing relay-contacts, and cleaned with "CRC QD Plastic Safe Liquid Contact Cleaner". As usual, this was all done under extreme magnification and lots of light. I got all surfaces of blade-pins nice and shiny again (and able to conduct electricity). 

I ordered parts to build a new GPS-Module cable and they arrived in a few days. Wires appear to be 30 gauge with thin flexible silicone-type insulation. Pins were much better than original ones and didn't have any strange plating on them. Crimps also looked fine. I carefully removed the Dupont (RC Type) pins from included single-position plugs and installed new pins/wires in a good 4-pin-position black Dupont plug from spare-parts box. Connection seems to be 100% now and not susceptible to drop-outs during basic flexing of cable or vibrations. During back-yard testing, I was getting a fast GPS-3D-Lock and good sats/hdop numbers. I'm calling it fixed.

New GPS-Module cable installed. Pic is good enough to see pin-outs.

I replaced the foam tape to be similar as shown above. I used 4-5 layers to make it as high as possible. The ceramic antenna on top is just barely touching the top plastic body cover (when fully installed) and seems to get the best reception this way (for this entry-level GPS Module that means just "acceptable").

Never again will I assume a connection is good, just because connectors are securely fastened (not on this model-aircraft anyway).

Upon inspection of Compass-Module, found the same problems. Luckily I ordered some extra parts to build more cables. New cable will end-up being about 1.0 inch shorter (but still reaches with length to spare). Like before, still had to carefully clean tarnish and corrosion from cheap imitation PicoBlade sockets themselves, soldered to the boards at both ends. Then, I installed the new cable.

New Magnetometer (Compass) cable
As you can see from the above pic, the pin-outs (for the stock Nova compass) are:
Update 2015-01: I have not had a single problem with GPS-Module or Compass since replacing these cables and cleaning away corrosion and tarnish (from the modules themselves).


  1. Hi, just wanted to say that you have an amazing blog! I've had my CX20 for a month now, and I've been having problems with my quad. I am able to fly the quad properly in manual mode, but when I do Stabilize, the quad hovers for a bit, then goes off to the left and I am unable to control it for some reason. Would you know what the possible problem is? I have an open source version... wrecked it the last time I tried to Auto-tune it... would be moving it to an s450 kit soon... was thinking what other parts I should replace to make it more stable...

    1. I'm not familiar with "Manual Mode". Some common APM Modes are Stabilize, Altitude-Hold, and Loiter. Maybe re-phrase your problem.
      After crash, did you do a full erase, reset, default params, and re-calibrate?

    2. Thank you for replying.

      I guess, Manual would be - Stabilize (Manual) SWB0 SWA0 and then the other mode would be Loiter (Stable) SWB0 SWA0 before I do Auto-Tune?

      So while under Stabilize (Manual) mode, I can fly the quad fine with it... it has a few yaw and pitch issues as it doesn't seem to be able to just maintain it's position. So I guess, I just need to trim it?

      Next though when I tried to Loiter (Stable) to trigger Auto-tune, as I said above, it holds it's position for a few seconds, then it just tilts to the left and just flies in that direction as if out of control. Never been able to regain control as it crashes onto something.

      Body got cracked last time I flew it. Also broke the stock skids last time it crashed on a tree. So my cx20 is currently using 2 noodles attached to the body via rubber bands. It now slowly yaws to the left when I try to hover. So I guess it won't be ideal to try to do those right now.

      Will try to do a reset then and follow your tips as soon as I transfer my cx20 to an s450 frame.

      Thanks for the info! :)

    3. You do not need to Auto-TUNE. Stock PIDs should be fine. Fully calibrate everything. Should fly Stabilize fine. A little drift is normal due to wind. Only thing it might need is in Auto-TRIM (see blog). Once you have that working, Loiter should hold position (if you have a good GPS Fix). Also uses compass so that's why I say "fully calibrate".


The stupid spammers have now forced me to approve each Comment before it appears (but I am usually pretty quick about it).