grundig: Grundig Majestic 3165 no FM

Hello, I have been working on a 3165 Grundig Majestic that has no FM reception. The other bands are working properly. All tubes are tested good. weak capacitors were replaced with exception of the main electrolytic multicap which is slightly high but does not seem to be a problem. I can detect no breaks or anything loose. Voltages to the ECC85 tube are as follows: 1=197v, 2=-.02v, 3=1.30v, 4=0v, 5=0v, 6=104v, 7= -.549v, 8=0v and 9= 0v. If I read the schematic correctly I should have 133v on pin 6 and 210v on pin 1 so these seem low.

Initially I very briefly was able to dial in one FM station but it was faint and quickly faded away. Nothing since. I suspected a bad tube and did find the ECC85 was also not as strong and would drop off. Replacing it with a strong tube made no difference.

Normally I am very successful with AM and SW sets and require minimal equipment. My experience with FM is limited. 

Thank you for your assistance and patience.

Mark

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Check the electrolytic capacitor on the FM detector (maybe an EABC80 but a pair of diodes is possible). Usually about 4uF @ 35V and + goes to chassis. These dry out.
A 4.7 uF at 40V is OK.

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Thank you for your input. The tube lineup for this is ECC85, ECH81, EBF89, ECC83, ELL95, ELL95 and EM84. Since I do not have the EABC80 I am assuming to still look at the ECC85? I do not have a proper schematic and have been trying to compare two of the models we have on the site here for some guidance. The only 4uf electrolytic cap I see is going to an ECC83 and it's reading a bit high at 7.2 uf.

Thoughts?

R/

Mark

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If there is no EABC80, the ratio detector for FM demodulation is probably realized with two germanium diodes instead, but principially the design is the same and there should be a capacitor of a few microfarads which can be suspect.

However, i have noted that some german radios from early 60's (in particular Blaupunkt car radios) do not have an electrolytic in that position, instead they use a paper capacitor of a smaller value, maybe around 0.5 uF.

Some other types of FM demodulators (Foster-Seely, Körting's "Syntektor", various quadrature detectors using special tubes like the 6DT6 etc) have also been used during the years but i dont believe that Grundig ever should have used anything else than the usual ratio detector during the tube era.

I think you should check that the local oscillator which is implemented in one half of the ECC85 is running. Most easily by setting up another FM reciever near the Grundig, tune it to a silent frequency in the upper part of the FM band and listen if you can hear a carrier from the Grundig's oscillator when tuning it back and forth.  Usually, the local oscillator frequency is 10.7 MHz above the signal frequency so if you for example tune the Grundig to 90 MHz , you should hear the carrier when you tune the other receiver around 90 + 10.7 = 100.7 MHz.

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The EBF89 will be last IF and the AM detector. So as mentioned by me and Torbjörn there must be a pair of diodes near or in the last FM IFT connected to the EBF89. A 0.5uF paper capacitor is also likely leaky. The capacitor, electrolytic or paper, feeds the EM84 grid for the FM magic eye action, probably via a resistor. In AM mode, the EM84 is fed from the EBF89 diode via resistors. I think a less than 2uF or a paper capacitor is unlikely on the Grundig. It will be using ratio detector or similar.

The idea of putting 2nd radio close (it will be 10.7 MHz different) and tuning the Majestic to low and high end of FM band is good.

Since you swapped to a good ECC85, the most likely fault is the capacitor to chassis on the FM detector diodes*. The next most likely is an open circuit FM IF, but usually the FM IFs and AM IFs are in series and so if there is good AM there is not that fault.

Then the wavechange switch to switch between AM and FM detectors to the volume control could be checked.

Note that old electrolytics reading low means "dried out" and reading high means "leaky". The ECC83 is likely an audio phase splitter. ·

" Usually, the local oscillator frequency is 10.7 MHz above the signal frequency so if you for example tune the Grundig to 90 MHz , you should hear the carrier when you tune the other receiver around 90 + 10.7 = 100.7 MHz"
Or if the LO is lower than RF then subtract 10.7 from the Majestic scale, thus 104 MHz gives a 93.3 MHz carrier on the other radio.

 [* There is no EABC80, nor any other suitable valve for an FM detector so there are a pair of diodes, similar to germanium 1N60, but they might be inside the last FM IF can.]

The Grundig 3260 seems similar and does have the two diodes in the IFT can and a 4uF capacitor. 

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The same chassis as the 3260 is the 3265 in a similar cabinet to your Majestic.

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Thank you all! I will work on this when I return next week from working out of town. 

Early in this repair I had tried the suggestion with another FM radio with no result and considered a problem with the oscillator. I will perform that test again.

Regards,

Mark

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Thank you all again. Myself and a friend will be working on this again this week now that I have some time. I will update when I know more.

R/

Mark

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