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eggfinder trs gps chip issues

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kzimmerman

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So I bought one of these, and shortly thereafter discovered that my soldering skills weren't up to snuff. So I had it built by a very knowledgeable person who works as an electronics engineer. I know he's done aerospace stuff. So, he built it, and he mistakenly didn't fill the well in the GPS chip, and consequently it came apart under the G-forces of flight. The tan part on top detached from the rest of the chip. He's awefully busy right now, so I figured I would post this question here. Can this be fixed? I don't think I'm going to have much success removing the whole chip and replacing it. He's got it right now, but I need to get it back from him to work out placement in a launch vehicle anyways.
Thanks
Kurt
 

cerving

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That's the patch antenna installed by the GPS manufacturer, it's held on by conductive tape and one pin that's soldered to the GPS' board. That's a common mounting method for patch antennas. It can become dislodged if you get a hard enough jolt. Generally it's meant replacing the entire GPS module, but I'm working on a way to replace just the antenna. Sit tight... I'll post it. In the meantime, I recommend that you use some heat-shrink tubing to hold the antenna onto the board, or a little bit of epoxy filleted around the edge of the antenna.
 

chuck5395

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That's the patch antenna installed by the GPS manufacturer, it's held on by conductive tape and one pin that's soldered to the GPS' board. That's a common mounting method for patch antennas. It can become dislodged if you get a hard enough jolt. Generally it's meant replacing the entire GPS module, but I'm working on a way to replace just the antenna. Sit tight... I'll post it. In the meantime, I recommend that you use some heat-shrink tubing to hold the antenna onto the board, or a little bit of epoxy filleted around the edge of the antenna.
That would be awesome. I've had to retire two Eggfinders because of this issue.
 

smapdiage9

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Ways people commonly guard against this happening also include using shrink wrap around the antenna and board to hold it in place.
 

ksaves2

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That would be awesome. I've had to retire two Eggfinders because of this issue.
If you're adventurous Chuck, you could try what I did. I took a cut-off wheel and very carefully cut a line in the base in half. If you go a little deep and cut a few traces, it's easy to make
and solder wire bridges. Next get the soldering iron good and hot. Lay it down as flat as you can get on the solder pads on one side and hold the whole affair upside down.
If you have a desoldering sucker, you can try to get as much solder off the pads in the "right side up" position first. The goal is to get one side of the base to fall off the board.
That's the reason I split it as I didn't have the means to heat both side at once. Now attack the other side and get that half of the base off.

Now repair and damaged traces with soldered wire bridges. Next, if this is the old v1 of the EggFinder, one can use the 3.3V terminals on the aft end of the board for power to a GPS chipset.
The final thing is to solder the TX out lead from the GPS chipset to the RCV in pad where the old GPS sat. It's on the lower left of the pad base with the antenna facing left. I can't remember for the moment if it's the most lower left pad or the one next to it. I can look when I get home and post it. That's it. Three wires from another GPS to the EF board two for power, one for signal and it will work again.
I did it twice already and one Ublox GPS receiver has a really reliable circularly polarized receiving antenna. The altitude reporting might be more accurate than the SirfIV device but I haven't been able to fly it yet.

I should have realized this was a possibility as my first EggFinder I built (right after they came out) lasted all but 15 minutes. Worked great until it fell 4 feet off the windowsill when testing
and the GPS antenna snapped off the base. It lived in my junk box until I realized it might be salvageable (while I was experimenting with making ematches one cold winter!)
I'm glad this has been reported as I've laid beads of Proline 4500 epoxy down both sides of the GPS antennas of my stock units. The fore and aft portions of the antenna base with the
solder pads is in too close proximity of other components so I didn't do a "four sided" reinforcing regimen. There are also slits there to allow air to get to components in the base so I STRONGLY recommend one lays epoxy on the sides of the antenna/pc board interface. That'll be plenty strong and I bet will out perform
shrink wrap. Kurt
 

scsager

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For what its worth -

I have successfully replaced the GPS module on one of my Eggfinder Tx units.

I purchased a replacement GPS module from Mouser electronics (Mouser part# 927-A2235-H), and used a ChipQuik SMD1 kit to remove the problem GPS from the board. While I was at it - I substituted all SMD components where possible.

I also have used 3/4" clear (For the TX) and 1" clear (For the TRS) heat shrink tube. Heat shrink and ChipQuik from Ebay.

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2016-09-25 12.47.46.jpg
 

ksaves2

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For what its worth -

I have successfully replaced the GPS module on one of my Eggfinder Tx units.

I purchased a replacement GPS module from Mouser electronics (Mouser part# 927-A2235-H), and used a ChipQuik SMD1 kit to remove the problem GPS from the board. While I was at it - I substituted all SMD components where possible.

I also have used 3/4" clear (For the TX) and 1" clear (For the TRS) heat shrink tube. Heat shrink and ChipQuik from Ebay.
That sounds nice. It seems one needs to apply the low temp flux solder to the pads and then did you use a heat gun to get it to release or did you have to hold two soldering irons on either side to get it to come off?

That would sure beat cutting and grinding and I'd give it a go next time I get stuck in that position. Thanks for posting. Kurt Savegnago
 

cerving

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No joy replacing the GPS antenna. I took a prototype TRS (one that I'd never fly), confirmed that it was feeding good GPS data to the receiver, then pryed off the antenna. I soldered on a replacement 15mm antenna... no satellites.

Apparently it may matter how the antenna broke off, I think it it breaks at the antenna side vs. the GPS module PCB side then it would probably work. Unfortunately, I don't think I've ever seen one break like that... they always snap off at the PCB, probably taking the hole-plating with it, which is most likely why it doesn't work.

So, it's a new GPS module... sorry, I tried.
 

ksaves2

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Looks like the Chip Quik method is the way to get the base off and put a new GPS on. The only caution is to avoid tearing a pad especially the signal out (Tx) and the power pads. Kurt
 

Suborbital Maniac

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That sounds nice. It seems one needs to apply the low temp flux solder to the pads and then did you use a heat gun to get it to release or did you have to hold two soldering irons on either side to get it to come off?
Hot air reflow is the *proper* way to do it but I don't have one of those so in general, here's the take on ChipQuik:

ChipQuik is a special low-melt temp alloy. The idea is to use it to 'contaminate' the solder on the board. There are a few techniques that have worked for me, depending on the situation. When individual legs are accessible, you can contaminate each joint, lift the leg up with pliers and work your away along. For fine pitch stuff, get lots of ChipQuik on and try to make a blob that shorts all the pins on one side of the IC. This way you have a single thermal mass to keep warm. Use your iron to keep the puddle liquid and gently use a tool to lift one side of the chip then let the puddle cool. Once the chip is removed, reheat and mop up the solder and clean up the pads for the new chip.
 

cerving

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It's not unusual to lift some of the GPS pads that don't have any traces on them, since there's not as much mechanical connection to the board on them. If they don't connect to anything, then it's not that big of a deal. The primary mechanical connection is supposed to be the 8 large pads on the bottom, which is why I keep revising the board to make it easier to solder those pads.
 
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