Hi Dave,
I do remember you asking about problems with your 706 a little while back :-
https://charlietangodxgroup.forumotion.com/t5400-problem-with-my-706-mk1#43847I've also heard of the 'fix' by cleaning up or replacing the relays (not for the faint of heart) and in general the relay/low pass filter board being wholly replaced in some units as a standard fix. (Most of the relays should be black plastic sealed units with the odd one white or yellow but I think that might be the MK II never seeing inside a MK I.)
This doesn't usually fix an 'AM' problem though, so is it a case of the radio working on other modes such as SSB/FM or just not working on a particular band? (We often get confusion on the forum where people state 'FM' or such when they actually mean CB frequencies.)
Either way I do recall suggesting that you get the radio looked at by a professional rather than tinkering with it yourself. Often there are 'easy fix' solutions posted on the internet that turn out to be anything but. Relays are fiddly enough to replace let alone strip apart in an attempt to clean the contacts or some such and I've only performed that a few times myself where I had no choice as a suitable replacement wasn't available. (Usually due to a different 'footprint' from standard relays and have even replaced them with suitable semiconductor transistor switching in desperation on TX/RX units.)
I think you'll have a hard enough time finding a working relay board from another radio to swap out and that won't be as straight forward as first thought. A proficient technician shouldn't find it too hard a job but there is some time involved as well as component cost with such and you would be charged appropriately.
I hope you get sorted and wish you well as I did before.
All the best,
Victor