[Mondial]

It depends on whether the plates are shorting as you rotate to the closed position, or if the local oscillator is dropping out as you increase the capacitance.

Do you get loud scratching sounds in the speaker as you close the tuning capacitor? That would indicate that the plates are bent and touching at some point in the rotation. If the stations you hear are at the right positions on the dial and the reception quits quietly then its the oscillator stopping at some point as the capacitance is increased.

You can check the operation of the local oscillator by listening for the oscillator signal on a nearby AM radio at a frequency 460 kHz above the dial indication of the 610. For example if the 610 is set to 1000 kHz, you should hear the oscillator carrier at 1460 kHz on a portable radio held near the tuning capacitor. You may have to tune around slightly to hear it, but a strong signal should be there if the oscillator is operating properly.