You may recall my disdain for the designers of the XM interconnection scheme on my Trailblazer. Here is a brief summary of the effort to repair the actual antenna in the event you find this sort of thing interesting. If not, carry on
The failed antenna reads around 15 ohms across it’s output. A good one reads about 7Mohm.
First pic is with the top cover removed
Second pic is with the antenna guard removed
Next, the board assembly removed, coax had to be removed to separate from housing and facilitate debug of circuit board. I was surprised to see so much circuitry without any conformal coating or other protection.
Now, a back of the napkin, first pass schematic to begin reverse engineering the circuit. All I want at this point is to find enough to begin the process of isolating various circuit chunks (the divide and conquer approach). No desire to reverse engineer more than I have to.
Removing resistors in line with various active components helps to isolate them. These resistors are 0102 SMT components, the size of pepper specks…
Second circuit isolated and the culprit is found!
The package marking V67 leads to the actual device, a NE38018. Once removed, the gate to drain is found to be shorted. This is a 13GHz HJ FET used in GPS and other high frequency designs. Unfortunately, it is also obsolete! A cross reference was found pretty quick (NE 3508M04) and readily available from Digikey/Mouser etc for $1.92 qty 1.
Parts on order, will be here tomorrow morning. Should be back and running shortly after that…