I will try to post here faults from various sources and how the problems were mitigated.
The post will be periodically updated.
Last update: May 29, 2022
1. Various sources. Lightning discharge near antenna.
This problem is fairly common and affects the receiving front end of the radio.
The fault is located on the Small Signal Board (the PCB that is exposed when the upper panel of the Main Unit is removed) and the fault can be repaired without removing it from the radio as the PCB is one side populated with components.
First, the RF is coming from the antena through a Rx/Tx relay (PA RF Board) to that small connector.
Let's explain what is near the RX connector. Here is the relevant part of the schematic:
On the left there are the two ESD protection components, D4 and D40. These are not regular diodes but specific protection semiconductors.
The original components are GBLC08I-LF-T7 but might be very well replaced with PESD2V8R1BSF. In order the protection provided to be effective, the replacement components must be connected in anti-paralell mode across the D4-D40!
If Rx is still not working, we must check the proper working of the Attenuator circuit, which is made with U31 and U32.
Those two circuits are similar to SPDT relays but they are semiconductors. In vast majority of cases I saw the issue, the problem is here also, at leat U31 is burned but U32 is still working.
U31 and U32 are located under the metallic shield.
The shield is not soldered and can be lifted with a sharp tweezer. Pay attention when you are removing it, be gently!
When you put it back, pay attention to the alignement of retaining clips on the PCB!
Pin 5 on U31 is on the middle of the LEFT side.
Pin 5 on U32 is on the middle of the RIGHT side.
You can test the RF then by putting a 22-100 nF capacitor from the pin 5 of U31 to the pin 5 of the U32 (or before and after the separation capacitors).
Here it is how:
U31 and U32 Original part:
Here is a picture sent by one of fellow hams with this kind of problem...
2. From Facebook Xiegu G90 Users, Ronan Cantwell