ts-850 atu iffy?

[m3vuv]

Hi all ive tried to adjust the null as per page 103 of the service manual,section 24.i couldnt seem to get it anywhere near spec into  a dummy load,manual says 50mv or less,since doing this i notice the auto tuner never stops,thats into a 50 ohm dummy load or my antenna with an swr of 1.2-1,the motors whir for a seccond but it stays in transmit and thats all it does,is this related,im not sure which was to procced with this,any pointers folks?,cheers m3vuv 73