Oh, sorry to hear this! If you do a Google search, sometimes you can find the factory service manual posted online. These aren't meant for players, and the companies don't routinely make them available to the public. But sometimes they are "leaked." If you can find such a manual, it may tell you a test sequence, such as holding certain buttons down at boot-up to run diagnostics.

The tip about loose connectors might be true if it was jarred or handled roughly. What happened before it stopped working?

I have a GEM module that has a dead battery for the keep-alive memory. It still boots, but it has to go through a lengthy load process every time, and it won't save the settings. Any good electronics tech that has skill of precise soldering to a PC board should be able to replace a battery like this.

You can also find replacement parts and whole non-functioning instruments sold on eBay. If it can't be fixed you could try selling it there. You might get $100-$300 for it, even in non-working condition. If you installed the video board, that can be removed and sold separately. A little extra money for a new Pa1000 maybe!

One thing someone on the Forum told me a long time ago, that I absolutely live by... These keyboards are like computers. Over time, spikes from lightning, etc., and "brown-outs" (undervoltage) damage the memory chips, the processor, etc. Especially older models like your Korg that take an AC cord without a power brick, ALWAYS plug them into a UPS / power conditioner. I wish you luck!