Sir kempga . . . . .
Me thinks that the mentioned resistance testing is to see if there is continuity between the F connection shell and the central pin connection going on into the internal FM tuner .
. . . if there is NO
series capacitor being involved in its circuitry design.
My left reference is showing the standard connection of a bit of RF parasitic wire with its proximity / capacitive coupling to the AC line to pick up and get some acquired FM RF into the radio.
That is the case in its factory shipped condition.
If more sensitivity is needed there is the option of external FM antenna input.
that metal boxed tuner schematic does not show on the main schematic, to see if a series cap is being inside.
That should explain all of that, UNLESS
your problem is related to AM reception in which case on your age of a set I believe that they had an external AM antenna loop that connects to the radio via a miniature phone plug in addition to and . . . . vice the F connector used on the FM section.
That connection goes into and feeds into a coupling winding on TP611 and TP 612 on the internal AM Ferrite loopstick.
You can get one of them via E-bay if yours is lost or if you are a second owner and never even knew
of such a possibility of that AM accessory existing .
Now . . .which is your situation ?
If its the AM situation, I can give you another alternative.
Tech Info Illustration:
73's de Edd