Once you get to Second Stage Boot (the Mega CD BIOS screen to fully load with logo, disc tray opens and game starts to read/spin) the next step is the Mega CD has to initialize the CD Processor and Sound Processor before it will display the Press Start to run text.

The typical symptom of being stuck at second stage boot is usually a permanently slow spinning disc and the text Press Start to run never showing up.

There are several things that can prevent you getting to Third Stage Boot.

The things that need to be working including all traces to and from them are:

The obvious starting point is tuning the laser. You may be actually getting to Third If it is a laser tune you normally see no disc spin, or spinning then stopping.

Confirm the laser is working using your phone camera over the laser head when no disc is inserted and it attempts to read a disc. The laser should glow red on your camera to show the laser diode is working.

If the laser is not the issue, usually the disc spins constantly when the laser is fine but there is another issue.

The ribbon connecting the CD to the motherboard, and its connector and traces are good place to check you have all good pins. It is rare they have trace damage, but common the ribbon is bad.

Swap it for a new ribbon is the quickest test.

The console will not get to the full BIOS screen with logo if there is a fully bad ribbon or bad CD drive, but it could also fail to load if they are just partially failed pins.

If the Bus Translator near the CD ribbon connector is bad, or any traces from it to the power board, Sound Source or Mega CD Engine are bad, it can prevent getting to Third Stage Boot.

Trace and bell out with continuity every single pin, including power, ground and all bus pins to their locations, and ideally replace with new chip if in doubt.

The Sound Source IC much also be fully operational and working, as well as its two RAM chips, and all connections between it and the Mega CD Engine and Bus Translator.

Swap the IC from a known working board ideally to confirm the IC is good, and bell out all pins and traces to their sources.

The RAM is the same as on the Game Gear and we sell it brand new here.

TO CONFIRM

The CD Process and its two RAM chips are needed to read the data off the CD and process it. If they are not working then you will be stuck at Second Stage Boot.

Swap the IC from a known working board ideally to confirm the IC is good, and bell out all pins and traces to their sources.

The RAM is the same as on the Game Gear and we sell it brand new here.