No GPS on MCA (0 satellites)

[Go4IT]

I'm working on the topic. If anyone had something valuable to add, please do so.
Attention: This topic is NOT about GPS Antenna issues! GPS signal from aerial is good, it's about a defect in the device.

Symptom:
The MCA satnav unit (but maybe also other types like NX and FX could be affected by the same issue also...) refuses to navigate because it does not receive any satellite (INFO button shows "0").

Setup:
Compare with signals of an equal working unit, using the same GPS antenna.
Also got parts from an wrecked FX/NX board

Tested:
- Plug is ok, signal can pass electrically onto the board without resitance
- Optical inspection was ok, no damage detectable
- Measured all MPs reflecting power supply for the GPS part (listed from schematic)
- Reflashed an updated the firmware to exclude software problems
- Chip get some programming sequence from OMAP on powerup (SPI interface of GPS chip traced with DSO)
- Chip sends data on AD-output line and also GPSCLOCK signal of approx. 16 MHz
- Quarz frequency is 16.384 MHz like on schematic

Conclusions:
The GPS chip (SN050...) seems to be alive as the outside signals are compareable with the one from the working unit, so it seems unlikely that it is broke.
Powersupplies are all ok and stable, even phantom-power on GPS plug.
The GPS signal itself is hard to check because it's in GHz band and demodulated inside the chip.

[Go4IT]

Finally i found the source of the problem, a inaccurate oscillator (xtal).

gps_xtal.jpg

gps_receiver_part_top.png