Possible short cirquit HELP PLEASE!!!

Hey i just bought an mpc 1000 used. The guy i bought from have not used for some time but assured me that it worked perfect. The problem is that the right side pcb board is acting totally weird and i think it might be a short cirquit on the board. Let me give some example of the madness. When i am on bank a and d and press the down arrow button the undo seq light but when i am on bank b and c I think it is the window button that light. The down arrow dont work at all. Another example is that if I press the undo seq button and the down arrow while i am on bank a or d it triggers the play function. The guy i bought it from are willing to give me my money back but i can also get for around 170 dollars instead. My question is if anyone have had simulair problems and know a way to fix it. I have read alot of posts and found some people with simulair problems but no solutions and I know the possibility of changing the whole pcb board but dont know if it could be solved by just replacing some tact switches which may create a short cirquit. So do anybody have any advise cause if i have to change the pcb board and the pads(When they die) then it will probably be better to save up and buy a brand new.....

Excuse my english i am from denmark..

Could it just be the ribbon cables that connect to the pcb aren't plugged in correctly or jacks are damaged. Have u tried unplugging them carefully and then plugging them back in?

(edit) Oh and i forgot to mention - while you have it opened up you can try cleaning the PCD with alcohol (not the drinking kind, the kind you get from the pharmacy with an absolute minimum of 70% alcohol, the higher the better as its mixed with water and you dont want water) and cotton buds/tissues. make sure you wipe it all off and blow it off with compressed air to get it perfectly dry. as maybe there's some flux on there thats become conductive and it just needs a bit of a wipe down.

theres many a youtube video on cleaning PCB's (generally accompanying a "how to solder" video) as well as removing the right PCB (look up how to replace tact switch/potentiometer on MPC)