Sony C48 RF interference

[emrr]

Not a lot to be read on the interwebs about these, but enough mention of RF problems to say it seems a trend.

Perhaps similar to the vintage Gefell problem?

Have one here with low level RF, fine for any loud source but questionable for low singing/etc.

Most interesting observation, having the battery/switch door open, today at least, kills the RF breakthrough.

I tried various grill to ground paths with no immediate luck.

Anyone been through this?

 

[Tubetec]

Heres the service manual ,

Maybe part of the casework isnt properly grounding , you could try cleaning the metal in the vicinity of where the case components meet . It looks like die cast metal , sometimes that can develop a layer of oxide on it .
Maybe it makes contact at two points forming a loop in the casework itself .
There seems to be a button either side with a steel clip on the inside that locks the front panel on , lightly polish the contact area where the steel meets the die cast , as there could have been a chemical reaction of some sort . Internal batteries left unattended for long periods can also cause a kind of electrolytic mould or crust on nearby components.

 

[Gus]

Have you checked the pin 1 to case connection?

I looked at the manual(assembly pictures) and it looks like pin 1 to microphone case is a mechanical connection not a soldered connection

With RF after checking shielding I think about diodes and RF filters maybe there is corrosion between pin 1 and case and a diode is formed


It looks like the amp board has a direct to case connection on the PCB(top view bottom right) and the power supply clear wire goes to pin 1


There are diodes D5, D6 and cap C16(9VDC battery filter) on the power supply board and C14 and C15 RF filter caps I would check if is not a case connection issue.


Interesting the RF issue went away with the battery door opened