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Old 13th Oct 2021, 9:39 am   #22
Join Date: Feb 2007
Location: Harrow, London, UK.
Posts: 1,013
Default Re: Grundig 5399/u/s

Hi Skip.

Hmm. This is very strange. Did you download the schematic and are you OK with reading it?

When you jumped the pins 2,3 &4 on the decoder socket, you in effect made the audio connection from the FM ratio detector to the audio amplifier as if the stereo decoder was not connected.

Using a screwdriver blade, touch the jumped connection, you should get loud hum, just as if you touched pin 1 of the TB socket when TB switch is selected.

If hum is present then first check if the tuning indicator is closing on the signal. If so then the FM stages are working OK and there is no connection from the FM Ratio Detector to the audio amplifier. Possibly a poor switch connection.

If no hum is present then the connection to the audio pre amplifier, 1/2 ECC83, is missing. Again a poor switch connection?

If nothing is obvious, then I suggest either adopt a external amplifier, a radio with tape in will do or, a temporary connection to the audio pre amplifier to use as a audio signal tracer. More to follow if necessary.

In the case of the coil, please photo it from a number of angles so that additional advice can be given.

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