yes everything can be fixed and you could get a custom chip from a parts board IF you can find the fault. that's the big IF.
repairing is very very easy. finding the problem is not.
Fixing PCBs and monitors is a lot different in my opinion. PCBs are digital with hundred of parts, many of them custom and all of it is unknown circuitry because there are no schematics. whereas with a monitor the circuit is infinitely simpler and there are less parts and most of it is off-the-shelf except the flyback and even then there is still one company making replacement flybacks so you could get that too. the problem with monitors is you can replace parts but if you miss something you power on and it blows up again taking out more stuff. you can start a fire or get zapped or worse, dead. that's why the guy gave you that advice.
anyone who wants to learn will get past that and just do it. this is mainly because now there is the net to fall back on and get lots of technical info and help. to do it properly you have to dedicate time, sometimes a life-time to the subject. this is why for example, guys who do body-building don't have a hobby playing and fixing arcade games in their spare time because they don't have any spare time.
there are places to start and a Mortal Kombat 3 isn't the right place. dead boards are the worst kind to fix because it means the program isn't running and the fault is in the CPU section or with some logic controlling the CPU and/or main work RAM. in most cases the PCB will just be resetting (watch-dogging) which means you have to disable that first before you can start otherwise all you see is a reset every 1 second. you also need proper equipment and some knowledge about digital electronics and how to read logic tables to find out what it should be doing. All that goes out the window if you are looking at a custom chip problem, assuming you can actually narrow it down to the custom.
To give an example, when I started repairing stuff I got hold of an original Missile Command. It was dead.
I looked and looked and looked and prodded and probed and got no-where.
I put it away in a box.
7 years later I pulled it out and fixed it in 10 minutes and I still have it here now and it still works 15 years on.
there were other times when I couldn't find the fault and went away and a couple of days later I looked again and found it, or did some research and got some ideas which helped.
but there were other times when I got so frustrated I changed every chip on the board including many custom surface mounted chips and it still didn't work! at that point the board was basically fucked but I wasted a month on it.
The moral of this story is the MK3 should go in a box and he should look for a working one on eBay if he wants to play it now, or he should get some help locally from someone who knows about board level repairs on complex surface mounted PCBs.
Not saying don't do it, just saying don't make it worse