MP-2 rear input needs fix

[Ekornbakke]

Hi guys.

The rear input on my MP-2 is weak, and somehow out of order. Sometimes there will be sound coming through, but with low gain and weak/unstable tone. In comparison, the front input works just fine. So, how do I go about fixing this? Is it possibly just a matter of tweaking something inside to make it sit tight again, or is there some parts that need to be changed?

[MarshallJMP]

Replace the front jack with a switchcraft L12-A (not a 12-A !!!),problem is not the rear jack but the front,because the signal from the rear jack is routed through a contact on the front jack.Now you can try to clean the contact with a piece of thick paper like a piece of a business card.I attached a pic,it's from the mp-1 but the jacks are the same for the mp-2.
You see the red circle?well put in a jack halfway so the contact is open,then put a small piece of paper between it,remove the jack so it's closed again and move the paper a few times between the contacts,this will clean it, and usually solves the problem,if not replace the jack.

Don't use sanding paper!!! because that will destroy the contact.