The reason why you don't find "proper" computer repair shops is the same reason as given above: economics. Why would you spend 2 hours troubleshooting a fault in an old P67 board when it'd be cheaper to take an Easyjet flight to mainland Europe, buy a board, fly back and swap it in. Let alone online ordering a 70 euro mainboard.
Your TV box example may work, provided you have access to plenty of donor boards, but ordering in parts from Ali/eBay to fix a £30 STB is heroic if you're a tree hugger but won't make you a living.
I do understand where you are coming from because I have experience of this myself.
Long short story... but it does end up back on topic
When I got my qualifications in electronics repair back in the early 80s I was taught to repair to component level (TVs and Videos) Some even still had valves in them!
My first job as an electronics repair engineer was with ICL and guess what - we were repairing computer PCBs to component level. While working there they paid for me to take a two year part time course in microprocessor circuit design and programming at the local university. After a few years break from electronics to work as a computer programmer I went back into electronics repair - working on industrial control electronics.
This was interesting and challenging job! In many cases you would have to reverse engineer a board with no schematics, build a test rig, sometimes microprocessor based, or at least program an eprom in assembly language to make the DUT do 'something' so you could test the peripheral ICs etc. And this was working from component datasheets only. Bear in mind there was no such thing as the internet then
This is also where I really learned to repair SMPS properly, which had a lot more complexity and discrete components in the early 90s
After that I went self employed building and repairing PCs. This was in the first half of the 90s. Now when we were repairing PCs at my computer shop, yes, we were just swapping boards Ram Processors etc and I thoroughly understand the economics of this. We were however repairing monitors (CRT ones of course) AT & ATX PSUs and things like Commodore Amiga computers to component level.
On one occasion I got my hands on a large job lot (a transit van full!) of faulty Amiga PSUs and Modulators from one of the big UK distributors. I don't recall what I paid or if they even just said 'come and get them' but it was not very much even if I did pay something. That proved very profitable to repair and resell - for a while we were the cheapest sellers in the country in the computer magazines of the time.
Another chance meeting with a trader at an amateur radio and electronics fair got me a contact who could get scrap from a big official Dell repair centre in Telford England - but he had no idea what to do with it other than dump it on the radio rally circuit. Within weeks I was buying everything he could get, running vans every couple of weeks to load up with scrap for a couple hundred quid a van full. Over a few months this got to be 7.5 ton trucks every week or two and I eventually had a larger warehouse/workshop near to the computer shop, two full time engineers working with me fixing this 'scrap' to component level and hey, we were turning over a very profitable business!
Unfortunately after a year or two 'corporate politics' got in the way and the supply of scrap dried up - but the point is the component level repair business was really profitable.
This takes us into the 2000s. Having got out of the PC business around 2002 when it seemed the boom was over, then running various other businesses basically installing AV equipment in clubs and bars, and having nothing to do with electronics repair for years other than solder the occasional connection, in the 2010s the I found the business had 'morphed' I was doing a lot of equipment rentals to the pub trade and had a lot of time on my hands while the main business pretty much ran itself - and I started buying spares or repair stuff of ebay or scrounging broken stuff off pub customers - mostly DJ and band equipment, lasers, intelligent disco lighting etc. And started fixing it to component level for profit. Though I only ever did this on a part time basis it was certainly very profitable generating £000's a year in my spare time
So that brings me to now I guess. Dismayed with the political direction my native country is now taking I decided I could not reconcile myself with that and the only reasonable response was to give up and leave them to it.
At least I (with the missus) brought net migration down by two lol
So here I am in Gran Canaria and need to make some money so I'm doing some repair work, mostly TVs at the moment - to component level - and making some money from that. Too soon to say if it will be profitable enough.
Recently someone asked me to look at a USB 1TByte hard drive. After a quick diagnosis it turned out it had a short circuit on the 5V rail. I asked the owner if it was worth the cost of repair and they said 'I could easily get a new drive but I could never replace the data on that one'.
I fixed a few HDDs back in the day and anyway tracing a short circuit on a HDD controller board is about the same as doing it on anything else. Actually I got a replacement second hand controller card first, was going to desolder the bios and fit it to the new card, then replace it. But at the last minute I decided to properly trace the fault for the experience of working on dense miniature SMD stuff. It was a short circuit SMD capacitor near the motor driver chip and it was soon working again, data intact - plus I have a spare donor board for future use maybe.
The owner was over the moon to get his drive and data back and that component level repair turned to be more lucrative than the TV repairs, he even paid me over the quoted price as a 'tip'
This got me into researching more about HDD repairs, which led me to badcaps forum and to here - researching about motherboard and laptop repairs. In turn I then found Louis Rossman's videos. This was something of an eye opener as I never really considered those sort of things to be repairable any more.
So yes I have years of experience of repair work as a full time and part time business - both running a computer shop building, upgrading and 'repairing by board swapping' PCs (profitable) and component level repair (profitable).
Now I'm wondering what the local computer 'repair' shops here are doing with all their scrap boards PSUs and drives.... I return to the UK regularly so could also bring some 'junk' back with me.
As it appears to be the common opinion that this is most likely an unprofitable venture (my past experience tells me otherwise so I just need to discover for myself), and very few apparently do this sort of work anyway as it is not economically viable, I guess that is why no one here really has the experience to say what BGA repair station at what price is really capable of what repair work?
Rich