Mediator M60A: How to switch the phono input on this radio?

Dear collegues,

I came into possession of a "Mediator M60A" radio, (see also the "Philips 320A-16") which I put back into operation but I have no found how to select the audio signal from the phono input excluding the radio one.

Looking at the schematic I only noticed a symbol on the connection of the PU input on the volume potentiometer that could have represent the switch I was looking for, but the potentiometer does not allow any other movements other than rotation with on/off. In other radios (see Philips BX690) I had seen that pulling the knob switched to phono.

Unfortunately also the documentation present on RMorg of this and other similar models did not clarify the problem, so at the moment I don't know what else to do to solve this problem.

For completeness I attach the part of the circuit involved and the photo of the potentiometer and I inform you that I have published the photos of the “Mediator M60A”, collected during the restoration work.

Thank you in advance for any help you can provide me.

Best regards

Roberto (RMorg Id=23538)

  

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Hallo Roberto

Das ist kein Schalter, sondern die Verbindung zur Abschirmung der Verdrahtung. An der Phonobuchse muss beim Einsetzen des Steckers ein versteckter Umschaltkontakt betätigt werden. Damit werden die HF-Vorstufen stummgeschaltet. Wie das ausschaut kannst du beim Schema vom Mediator M72 sehen. Da wird die Umschaltbuchse vollständig sichtbar.

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Jörg writes (parparsed)

This is not a switch, but the connection to the wiring shield. A hidden switching contact is activated on the phono socket by inserting the plug. This mutes the IF amplifiers. You can see what this looks like in the schematic of the Mediator M72, where switching socket becomes completely visible.

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Hi Jörg & Michael,

first of all thank you very much for your very fast clarifications, following which I thought that the problem could depend on false contacts and therefore I cleaned all the contacts and the potentiometer and re-ran the tests and now everything seems OK: when I insert the plugs into the PU the radio signal decreases almost completely, while that from the PU input can be heard well, but not with the same intensity as the radio one.
Previously, perhaps due to bad contacts, or frankly I don't know what else, I heard the radio signal strongly overlapping with those coming from the PU input..

Frankly, however, I still don't understand, probably due to my poor theoretical preparation, how the switching between the radio signal and the PU signal occurs, which in the M72A, if I interpret the diagram correctly, the P socket is connected to ground when the plug is inserted but in the M60A when I insert the plug I don't measure a connection to ground.

To summarize everything I attach a photo in which I highlight the PU circuit of the Mediator M60A indicating the differences with the Mediator M72A

I thank you again for the support you have provided me and I greet you cordially.

Roberto

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