Tascam 112 RTC

Dear all,

looking for help in finding the solution for a speeding real-time counter of a Tascam 112MkII. It is a NOS deck, everything works smoothly, except the time counter which runs at approximately the double rate for any length of cassette. The service manual does not mention any calibration, so it must be a fixed-value circuitry. Also, there are no schematics in the manual, except the PCBs and component values.
Has anyone had a similar problem with this deck and how to solve it? Thank you in advance.