Electronic – How to find inductance of a burnt inductor of a RF matching circuit

gpsinductor

I have an Android headunit for my car with wifi, gps, 3G, etc. At some point the GPS stopped working. I replaced the antenna connector because the pin was bended and could not connect anymore. At the beginning the gps was working for a while and then dead. GPS can see satellites but gets not SNR. I took apart the HU and see that there is a burnt inductor at the matching circuit of an active the antenna (see photo). I think it makes sense that it was working fine but after a while it burnt and had that behaviour. Now it gets no SNR at all. I guess if burnt badly after all.

enter image description here

Here there are a Ohm resistor (top) , burnt inductor (middle), inductor (bottom right), and a capacitor of 4.7uF (bottom left).

I have the schematics of this, but it corresponds to a part that is "optional" (see schematics).
enter image description here

I'am no expert at all in electronics, so I need help here. I think that the burnt inductor is M5002, which the description says is 10nH 300mA. The M5003 says nothing, there is no info there. How can I be sure that the burnt one is M5002? (I have no LCR meter at the moment).

Any help will be highly appreciated.
cheers.

Update 1 :
I am quite sure what is burnt is an inductor see photos attached. enter image description here

enter image description here

Then, @JRE in this photo it seems as if the empty pad is connected to the antenna pin (I would say GND?) can you confirm?
enter image description here

Best Answer

I removed the glue and figure out some of the parts. But still cannot understand the whole thing. However, I think @JRE is right and the burnt resistor is not M5002 but M5003 as it is the one that carries the line from the antenna, and for which I have no data. enter image description here

Update.

After loads of reading I could figure out that the burnt inductor was actually a choke to bring power to the antenna. That's why shortcutting the antenna burnt it. The only function is therefore power, therefore it should block all frequencies in the range if gps antenna, as it was a dedicated gps antenna. The right inductor for the job could be a 27nH (max inductance at 1600MHz).

That's what I did, replace it and now the gps is getting signal again!

Related Topic