T522 1´ Tone missing

[KaMoe]

Just bought back the T522 I sold in the late 70ties. :-)
Some of the drawbars needs cleaning, but that is of no concern.
What concerns me is that the second F key on the upper keyboard is missing the high (1´) tone.
And it is the same for the F key on the lover keyboard just below. (See picture. Missing tone is marked with the red dot)
Any suggestion on where I should start looking for the solution?
Thanks in advance.

[enor]

Is the same frequency missing from the other places where it should appear? For instance, the F keys one octave up on the 2', and two octaves up on the 4' (among other places)?

[KaMoe]

Yes, you are right. It is also missing in the places you mention.

[enor]

Then you have a broken wire connection at the tone generator. The note you're describing corresponds to frequency #78, which is the 4th terminal from the left on the generator terminal strip.