The reason has been identified: the +5V voltage on pin 14 is used to keep the display in an active state. However, Yaesu did not design it with sufficient robustness, leading to excessive current flow on that pin when connecting certain devices, which caused the fuse to blow and resulted in no output.
Source of U2B:
The F1801 fuse has a rated current of 630mA and a maximum operating temperature of 70°C. However, the RB521S-30 diode at the D1800 position only has a rated maximum continuous current of 200mA. Therefore, the DVI circuit cannot actually provide a safe voltage exceeding 200mA. Interestingly, the latest Yaesu FT-710 also has a similar DVI circuit, which uses a "PolySwitch" self-resetting fuse that maintains a current of 350mA at 60°C and a tripping current of 700mA. The RB160M-30 diode at the D1800 position has also been changed, with a maximum rated continuous current of 1A. Therefore, it appears that the FT-710 can safely provide up to 350mA of 5V voltage. The latest FT-710 also includes a TVS network on the DDC_SCL and SDA lines.
The design in the 710 is much better than DX10; DX10 required disassembly and repair of resistors after failure, while the 710 can self-recover.
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