Ivan_Eng

The problem is resolved.In order to “revive” the topic – I will not write an answer … yet. Ask your questions.

A flag GS appeared on the PFD display, the Garmin GNS430 msg on page about a malfunction of the glide path receiver board – G/S has failed.The glideslope receiver board was replaced, the GS flag disappeared on the display.It is interesting to find the cause of the faulty board and how does the flag appear on the display from the glide path glideslope receiver board? Via arinc 429 bus or directly by voltage signal? Powered GNS 430 from a power supply unit with a voltage of 25 V and a current of 1 A. The unit started up, measured the voltages on the J25 connector of the glideslope board, and also compared several voltage points with the working board. On this forum I read that perhaps the problem is related to the double-gate mosfet (tetrode BF995), which is in the input stage. Also on the forum, they advised the documentation on the glideslope receiver BENDIX / KING KX165A – I looked through its diagrams, the principles of operation of each stage and, by analogy, called the control points on the glideslope receiver GNS430 board. With the board connected, on the message page MSG GNS430 writes – G/S has failed. When the board is disconnected from the NAV BOARD, the message changes to – G/S is not responding. These actions suggested that the board may be “conditionally live”, and the point is in some cascades / elements, but not in the INTEL central processor – if, of course, it’s in it, then I think it’s unrealistic to fix it … Then I connected via arinc429 to the P4006 connector (legs 23 and 24). Received data on labels 173 and 174. A working glideslope board successfully accepts the input signal and the DDM changes from zero within acceptable limits (no LOC/GS antenna connected) The faulty one issues the SSM status bit – as FAIL, this signal is likely and forms the output of the flag on the PFD – GS. In general, I do not know which glideslope section / module of the board is defective. I did not check with the signal from the IFR4000 generator applied to the board input, except with the GNS430 installed on board and the standard antenna. Advise based on your experience – it may be the cause of the BF995 mosfet or it is in other parts of the glideslope of the board (amplifiers, attenuators, mixers, etc. I found the schematic for the GNS430 RF section, but there are many similar nodes in it, such as PLL, VCO and LD signal to the controller and the output of their UART controller.Also, the LM317 power stabilizer and 3EM(VHF/UHF Transistor) in the VCO generator.For some reason, a digital potentiometer is used for feedback, like the bendix / king KX165A, but on my glide path board I did not even find a digital potentiometer microcircuit – perhaps they still implemented it in the communication board and control it by uart.Measured the input and output parameters of the PLL:From good board – OSCin:12Mhz and Fin: 290 MHzFrom bad board – OSCin:17Mhz and Fin: 290 MHzThe fin frequencies OSCin are different, because the crystal oscillators are one at 11.975 MHz and the other at 16.800 MHz. From the Bendix / King KX165A documentation states:In a normal synthesizer locked state, the LD of U3011 (pin 7) will be high.Low going pulses will be seen at the LD output if the synthesizer is unlocked. GNS430_schematic.pdf King KX-165A Maintenance.pdf