Japanese Super Game Boy on American SNES shows black screen

I recently acquired a Japanese Super Game Boy adapter and it's not working on my American SNES. My SNES is a SNS-101 and I removed the upper part of its carcass, so Super Famicom games can fit on it (I have a bunch of them and they all work perfectly on this same SNES). If I put in the Super Game Boy, though, it only shows a black screen, with no sound, regardless of the presence of a Game Boy cartridge on the Super Game Boy itself.
Could this be happening because of some kind of region locking? Or perhaps, the Super Game Boy is broken? If it's broken, is there any possible way to fix it?
I took some photos of the Super Game Boy internals: https://www.flickr.com/photos/127415454@N03/albums/72157668405888454
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How do I fix black screen on Super Nintendo?
The Gameboy systems as a whole actually have no regional restrictions. This means you can play any Gameboy game on it as long as your system is the same system as the game is made for.Are super gameboys region locked?
Before we begin, exactly what is a Super Game Boy 2? To put it simply, it's a better version of the original Super Game Boy. It works with any region of game and it's even compatible with your North American Super NES after a minor modification (more specifically, removing the tabs located in the cartridge slot).Does Super Gameboy 2 work on US SNES?
Insert any Game Boy cartridge into the Super Game Boy. Insert the Super Game Boy into a Game Genie. Insert the Game Genie into the SNES and power on the console. Game play will be in slow motion without sound.How to Fix SNES With No Signal | RUMBLEBOX Repair
Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.
Images: Ketut Subiyanto, Ketut Subiyanto, Muhammadtaha Ibrahim Ma'aji, Monstera