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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 13th Oct 2021, 3:17 am   #21
Vecher1
Triode
 
Join Date: Apr 2021
Location: Lansdale, Pennslyvania, USA
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Default Re: Grundig 5399/u/s

ok when I jumpered the pins 2,3,4 no difference in audio..

on my coil I only see 4 wires.. not 5 cannot find where the other wire attaches to the coil for the center tap..

So I guess In am out of luck there.

Skip
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Old 13th Oct 2021, 9:39 am   #22
simpsons
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Location: Harrow, London, UK.
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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.



Chris
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Old 13th Oct 2021, 7:54 pm   #23
Vecher1
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Default Re: Grundig 5399/u/s

Chris, Ok thasnks Will do.. No problem on reading schematic..

I have most all test equipment

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Old 14th Oct 2021, 10:01 am   #24
simpsons
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Default Re: Grundig 5399/u/s

Hi again Skip

So, to recap, with the stereo decoder board removed, there was no FM audio. This we can agree is no surprise as the 9 pin socket use to connect the board to the main chassis was now unplugged.

The fact that feint audio could be heard is likely due to the self capacitance in wiring but it says that the FM stages are working.

The 9 pin socket to the stereo decoder carries both heater and HT supplies to the decoder and presents raw audio on pin4. It also switches the decoder to mono, by earthing via the piano switch (stereo), pin 5. The decoder, when working, outputs stereo to pins 2&3.

Ship, just double check all this is happening in case there is a clue to what is going on.

So, as mentioned earlier, joining pins 2,3 & 4 should give you plenty of sound. My schematic doesn't show the decoder socket, which is really bad news, and for some markets it isn't fitted!!

To audio signal trace, we can either inject audio from a suitable source or using a an amplifier check the audio present on the Grundig from the ratio detector, onwards. A suitable starting point, as shown on the schematic, is R36 22k ohms.

There must be a reason why this fault is proving illusive, I wonder what are we are missing?

Chris
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Old 15th Oct 2021, 2:46 pm   #25
simpsons
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Default Re: Grundig 5399/u/s

Skip

I've managed to find the Grundig radio schematic which shows quite clearly how the decoder socket is wired in your radio.

It is from the Grundig KS55,560,565 and 570 series of radiograms.

Use the Radiomuseum site as the schematic image is very clear.

There are some differences in the component values & the audio stage of the radiogram but, as with most Grundigs, you can soon see how their engineers built upon a good design incorporating the stereo decoder 4.

Hope this helps


Chris
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