1 - If the equipment was used in a dusty environment, it is likely that the fault is the potentiometer. If the potentiometer tracks have some dirt, it may be that they are not making good contact. There are many products to clean potentiometers, you must remove the radio cover and there you will see it, you do not have to disassemble anything else, it is not necessary to desolder it, you just have to apply a little contact spray for potentiometers and turn it several times until that is cleaned, sometimes it turns out and the problem goes away, other times you have to change it. 2 - You should also check that all the potentiometer legs are well welded, to make sure you can solve them again, you just have to heat them with the soldering iron and with the same tin that it has solved. 3 - Finally check the contact pins between the front panel and the main board, there are several tabs that connect with cables to the front panel (connect the display, potentiometer, speaker, etc.), it can be a bad contact there, in those tabs , disconnect them and add some cleaner like WD40 or some similar, then dry well and plug everything back in.