telefunken: 5430MX (5420 MX) Hi-Fi; Opus --- poor FM recepti

ID: 193727
? telefunken: 5430MX (5420 MX) Hi-Fi; Opus --- poor FM recepti 
03.Jul.09 02:26
0

Alain Dufour (CDN)
Articles: 38
Count of Thanks: 7
Alain Dufour

Hi everyone,

I just bought this superb set. No hum and a very good sound quality. However I do have one problem with FM receiving. There seems to be a "shadow" station and even with AFC pushed in, frequencies will slide or "jump" for no apparent reason or when I get closer to the set. I am still a newbie (that is I don't have much equipment to make sophisticated tests) but my problem maybe an easy one to solve. Any ideas /tips are welcome !


To thank the Author because you find the post helpful or well done.

 2
? Clean contacts with DeOxit 
03.Jul.09 19:29

Joe Sousa (USA)
Editor
Articles: 669
Count of Thanks: 4
Joe Sousa

Hi Alan,

This is the main radio I listen to in my home lab.

I have had trouble with the piano key band switches.

Currently, I actually need to repair them because the stereo button does not stay down.

Have you cleaned your switches? I recommend DeOxit. The US military uses it to stay connected...

But you say that you notice an effect when you walk by.

The only FM radio that I have that I have that does this is the Radio Shack Realist tuner.

If the 300 Ohm twin lead is moved near the front end, the front end will oscillate and block out all but the strongest stations.

Could it be that a bad tuner shield connection in your 5430MX is loose?

Regards,

-Joe

To thank the Author because you find the post helpful or well done.

 3
? What Antenna is used? 
03.Jul.09 20:39

Hans M. Knoll (D)
Editor
Articles: 2163
Count of Thanks: 5
Hans M. Knoll

Hello Alain.

hello Joe, maybe i can help here?

In order to give an answer for this problem, questions are still open.

Which antenna is used?
The one built-in in the case?
 

Which frequency do the two  station use?

.
Declaring the precise distance. For example. 95,0 and 95,2 or something.

The pressing of the AFC Taste makes the problem only greater!

If Selektivity not sufficing with good limitation, however, in a radio,

a turn-off level change of 1 is 3dB, is between two stations sufficing, in order to make the second station audible.

Technical „Capture Ratio” is busy.

 

regards hans m. knoll

 If you need information? see here on § 6.13

 

 

To thank the Author because you find the post helpful or well done.

 4
Antenna and De-Oxit 
04.Jul.09 02:52

Alain Dufour (CDN)
Articles: 38
Count of Thanks: 5
Alain Dufour

Hi Joe and Hans, thank you for your replies.

Here is what I have tonight...

Without AFC, I can tune 107.5 almost anywhere on the dial when I move the dial knob (and I can see the FM Tuner moving as well of course). Signal is quite strong. And 95.1 is also audible although not as strong a signal. Plus, I get other stations as I move... It does it even after more than thirty minutes of warming up.

With AFC ON, I can listen to 95.1 perfectly and then 95.9 wil come in from time to time. Or 92.5 and then it jumps to 93.5.

The antenna I use is the built-in one, as I do for similar german radios of that period (such as a Rossini  and a Telefunken Concerto). I did try a 300hom TV antenna yesterday but it did not seem to change much.

As for contacts, I just sprayed some deoxit on them.  I must admit I have one broken "glider switch". It was the AM white plastic glider that broke where it attaches a small metal rod linking it to the external white push-button. I removed one of the SW glider switch and  reconfigured the metal contacts to install it in the AM slot as I do not often use SW. But the drifting problem was present before I did that change.

I will experiment with other antennas and try to read bit more about shielding.

 

To thank the Author because you find the post helpful or well done.

 5
Spurious oscillation? 
04.Jul.09 04:49

Joe Sousa (USA)
Editor
Articles: 669
Count of Thanks: 3
Joe Sousa

Hi Alain,

The station changing when you walk around only suggests to me that there is a spurious oscillation, probably right at the front end.

You could verify this by listening for this oscillation, which is probably a pure carrier tone, on another FM radio. The oscillation should be very strong if your body position affects it.

If the front end is oscillating, it's frequency will probably change with the tuning knob, such that if you have another FM radio nearby, tuned normally to a radio station, then this station gets blocked out when the oscillation from the Telefunken is tuned over the station heard in the second FM radio.

You could also look for the spurious oscillation in the second radio by tuning through it's dial and finding a spot of dead quiet, that can be tuned away by the defective Telefunken.

The AFC control may also be part of the problem.

Regards,

-Joe

To thank the Author because you find the post helpful or well done.