Well, really hard to say.
Was this one of the original symptoms ?
Most strange and unexplainable faults in these decks are caused by
capacitors, cracked solder joints and, even worse, broken PCB copper
tracks. The copper traces tend to crack where a track meets a solder pad
which makes it very difficult to spot.
The boards are quite sensitive to heat in this respect so be careful, use
a good iron and good quality solder.
In your case, it seems that the basic functions are OK in that the carriage
is able to move both ways, the tonearm lifts, lowers and tracks, the motor
spins etc. but the controlling and/or sequence of the functions is not 100% working.
Of course, another component could be at fault here but make sure you
replaced ALL electrolytic caps and got their polarity right. Resolder all
edge connectors and ribbon cable joints and any other joints that look bad.
I'm sure you already did this but do it anyway. I often find more faults
under a microscope or better lighting and the more I look the more present and
potential future faults I find.
Also resolder the CPU socket inside the metal case and check the adjustments
of the << and >> buttons.
Martin