Lowrance gps antenna repair

[sämäx]

Hello people!

Me and my friend accidentally dropped our lowrance sonar. Yesterday I took it apart and did visual inspection to the pcb. While inspecting the pcb I saw two passive components had fallen off because of the impact. I tried to search for the components inside the case but didn't find them. I know that its quite far fetched to ask for the exact values for the missing components but is there some kind of rule of thumb that I could use to get the antenna working again? If not, does anyone possibly have any proposals how to proceed with this repair project?

In attachments, first picture shows the gps circuit from the backside of the pcb. The next two show the antenna circuit from the front side missing the two passive components.

Thanks for the help in advance! Hoping to get soon back to fishing 

[wraper]

The next two show the antenna circuit from the front side missing the two passive components.

There is only one component missing. Smaller footprint never had component populated.

[ChuckDarwin]

The missing part is probably a capacitor (C) somewhere in the 2.2-80pf range.  The white smd part is an inductor (L) [I've seen white caps and resistors, but rarely].  Together they form the matching network (LC) for the antenna system.  As @wraper said, the lower pads are unused.  It is there to give the manufacturer flexibility in selecting and tuning an antenna system.  Without a schematic or testing with a VNA, it will be hard to determine the value of the missing component. 

• You could try emailing Lowrance and tell them you a have an out of wty device and you would like to repair it.  They might be willing to tell you the component specs.  If it is in wty, have it repaired.
• See if someone on Lowrance forums knows or can measure the value
• Do you have an external antenna port through which you rig an external antenna?
• If you are comfortable soldering, you could try 10, 4,7, 16, 2,2, 22, 47 pf caps and see how well the signal locks on.  If something is close, then try closer values slightly up or down from that value.  Brute force approach.

[wraper]

The white smd part is an inductor (L)

It's multilayer chip antenna, not inductor.

[ChuckDarwin]

I was referring to the white (grey?) smd directly next to the missing part, not the chip antenna at the board edge.

[wraper]

I was referring to the white (grey?) smd directly next to the missing part, not the chip antenna at the board edge.

It's completely usual C0G MLCC cap. They usually are light grey or slightly pink. And yeah, it's grey, quite far from white.