When I power it on, it gives the error message below (the figures are not accurate as I copied and pasted it from somebody else's post who has had a similar issues as mine. )

I would not make any moves based on someone else’s error message that might have a similar issue. Nor would I make a decision based on such a telephone call to a service center.

The way most repair services work is they will take a look at your product, run diagnostic tests (which will pinpoint the issue) — it is at that time you can find out not only what the problem is, but exactly what your options and cost of repair should be... all before work begins.

This may vary some depending on where in the world you live... but repairs do not take place until you get an diagnosis of what is the exact problem. The cost of parts is one thing, the repair shop’s ‘bench time’ (what they charge for labor) is another. Those two things must be agreed upon by you before service can begin. (Here in the USA, for example, they have to give you, on request, the old parts that they replaced... this prevents them from charging you for things they did not replace).

The fewer “what if’s” the better!
What if ...your problem is different from the error message you provide — the wrong repair would take place and you would be out of luck... as it wouldn’t necessarily be what’s wrong.

I think the service center gave you the smallest and the largest things that could potentially be wrong.
A capacitor might be the smallest, least expensive issue; while an entire motherboard would be the largest, most expensive repair.
(...like the difference between replacing a spark plug versus replacing the engine of your car).

I’m pretty sure they would need to run the diagnostic tests to determine which is exactly the case. Exact error message IS important.

I agree it sounds like a simple problem (a loose or broken connection) - because, you say at some point it does work, normally. If it was the entire motherboard (expensive) the unit would likely never boot up and play AT ALL.

DO NOT ATTEMPT TO REPAIR THIS YOURSELF (capital letters for emphasis!)
Do not let friends (no matter how good they are with a soldering iron) attempt to fix something they are not sure is broken.

Your best bet is to call Yamaha Customer Service.
Talk to a Yamaha technician — and take their recommendation.
They may recommend a local service center, or they may even be able to direct you to some other solution. Certainly worth the call.

Because things maybe different in your part of the world (with the pandemic, et al) but start by getting in touch with your regional Yamaha distributor (listed in the back of your Owner’s Manual). They will be best to direct you under current conditions.

Let us know.