hifi engine

aiwa ad m700

hello to all ,
i have an aiwa cassette deck ad m700 and i have a problem with this deck
i've changed all belts and lubricated mechanism and and all swiches and potentiometers
regarding mechanism it's all fine
the problem is that when i press play on the right channel the vu meter is acting like crazy and the
sound either lowers itself or it is distorted and cutting out. i don't see a normal recording switch so i
cannot spray some contact cleaner in it and even in recording mode the same fault occurs.
if somebody please can help me i really appreciate it