hifi engine

Akai GX 630 DB Reel to Reel. LH Channel Quite on input. Output OK.

I have an Akai GX 630 DB Reel to Reel.
On the left hand channel, the output stage on playback of a previously recorder spool works fine.
Unfortunately, the LH Channel on record (Inputs stage) is silent.
Any ideas on what the problem could be?
All leads checked and interchange.
Looking through the User Manual there is a note from the previous owner setting out that this problem has occurred previously. Unfortunately, there is no indication as to whether the problem was rectified by an Engineer or whether it sorted itself out.
Any assistance would be most appreciated.