Resolve HDMI Output Issue on Raspberry Pi 4

I’m running the piSDR image (https://github.com/luigifcruz/pisdr-image) on a Raspberry Pi 4 that is dedicated to a small HDMI monitor. The system itself boots—confirmed by network reachability and LED activity—but the screen stays completely dark from the instant I power on. There is no splash screen, rainbow square, or blinking cursor; just a “no signal” message from the monitor. I have not yet tested a second display, so the fault might lie in the Pi-to-monitor handshake, EDID, or config.txt settings rather than hardware.

What I need from you
• Pinpoint why the Pi produces no video on this small monitor when using the current piSDR image.
• Supply and document the exact changes—whether that’s edits to config.txt (HDMI safe mode, force hot-plug, custom group/mode), kernel parameters, or firmware files—that make the image show video reliably from power-on.
• Provide a short verification guide so I can reproduce the fix from a fresh flash in the future.

Acceptance
I will re-flash the official piSDR image to a clean micro-SD, apply your modifications exactly as provided, power up, and see video on the small monitor without needing any extra commands or cables. If the display comes up consistently, the job is done.