Best answer: The Raspberry Pi 400 uses a unique mainboard to house all the components and connectors that isn't sold separately at this time so repairs aren't something you can do yourself.
There aren't many parts
If you watch a teardown video of the Raspberry Pi 400, you'll see that inside there are really only two parts outside of the plastic casing itself: a mainboard and a heatsink. The heatsink spans the length of the keyboard and also keeps the board and the whole keyboard from flexing too much, so it does double duty. And that's it. Really.
That means "repairing" a Raspberry Pi 400 would be removing a mainboard that's gone bad and replacing it. It's actually really easy to open the casing and removing those two parts is just as simple. The problem is that you can't buy one separately. At least right now.
On the official Raspberry Pi forums, James Hughes, the principal software e and forums moderator for the company answered the question about making the mainboard available when the question was asked.
This makes sense. Hobbyists that might be interested in using only the board inside a housing of their own design or anyone interested in repairing a Raspberry Pi 400 on their own probably aren't the target audience because the original Raspberry Pi 4b exists and is wonderful at doing the exact same things. Besides, the mainboard would probably come close to the price of replacing the entire unit.
Personally, I like to know I can fix the consumer electronics I buy on my own, though that's becoming more and more difficult. But in this case, I make an exception because the design is so simple and the cost of replacing the whole unit is really cheap. If I want to build a project of my own that doesn't require a keyboard or needs a smaller form factor, I'd buy another Raspberry Pi 4b.
Raspberry Pi 400 kit
Everything you love about the Raspberry Pi 4 gets squeezed right into a great keyboard! With this kit, all you need to provide is a screen.
Raspberry Pi 4B 4GB kit
For all of your projects
This kit has everything you need to get the Raspberry Pi 4b up and running, but you'll need to supply extras like a keyboard and mouse.
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