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Old 19th May 2009, 4:15 pm   #21
Steve_P
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Default Re: Grundig 2043 gets louder after 1 hour. Ignore/Worry?

Why not put a resistor in series with Pin 1 of the magic eye valve. Might enable you to see what's happening.

Cheers,

Steve P.
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Old 19th May 2009, 5:33 pm   #22
kalee20
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Default Re: Grundig 2043 gets louder after 1 hour. Ignore/Worry?

Measuring between pin 1 (negative) and pins 2&4 (positive) will tell you what the magic eye is seeing, even after it's fully open. Use a DVM or something with a very high input resistance.

The advantage of looking at the magic eye's DC signal input, is that it's a nearly infallible indication of the signal strength reaching the detector.

Incidentally, I can't see Steve P's sugestion doing much - as pin 1 is the grid, adding a series resistor won't affect anything. Or (always possible!) does he know something that I don't?
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Old 19th May 2009, 5:38 pm   #23
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Default Re: Grundig 2043 gets louder after 1 hour. Ignore/Worry?

I thought that it might make the reading go down, so that it could be read. Might be complete tripe, but it seemed to be worth a shot.

These sort of faults are hard to find, and with the set out of the cabinet, the problem might not appear....

Cheers,

Steve P.
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Old 19th May 2009, 6:15 pm   #24
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Default Re: Grundig 2043 gets louder after 1 hour. Ignore/Worry?

OK.

Adding a series resistor will reduce the sensitivity of the magic eye - provided another resistor is connected directly between pin 1 and pins 2&4 (which are chassis).

I'd suggest 2.2megohms in series, and 1 megohm in shunt.

Yes, removing the chassis may make the fault not happen! And at the moment, we don't even know if the 'loud' condition is normal, with the preceding 'quiet' being wrong, or vice versa!
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Old 19th May 2009, 6:51 pm   #25
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Default Re: Grundig 2043 gets louder after 1 hour. Ignore/Worry?

Quote:
Originally Posted by Steve Browne View Post
At this stage the magic eye only registered up to half strength even on strong local FM stations. Once the HT had been dropped to the correct value the same stations produced full deflection of the magic eye (which surprised me!).
It surprises me too. Changing the HT by this amount shouldn't affect the magic eye much, so the voltage being fed to it from the AGC must be varying. I'd expect the radio to be more sensitive at the higher HT voltage, increasing the AGC voltage and deflecting the magic eye further. My guess is that something somewhere is breaking down depending on time and the HT voltage. It may be worthwhile deliberately dropping the HT to say 50V below where it should be. The radio should still work reasonably well at this voltage, and my suspicion is that the fault will go away.

This won't identify the fault though. All the advice about checking circuit voltages when the fault is present is still good.

Treble check that you haven't missed a capacitor somewhere

Paul
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Old 20th May 2009, 10:17 am   #26
georgesgiralt
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Default Re: Grundig 2043 gets louder after 1 hour. Ignore/Worry?

Hi !
I own a couple of 3397 stereo sets from Grundig.
This morning, I came across a behaviour like the one you describe except it is in reverse.
I turn the set on, and after about a quarter of an hour, the volumes goes down. (about half the previous level)
Funny I thought as I was reading the forum !
So I turned the set off for some time (to get a coffee and an apple...) and repeat the experiment.
It came as the first time. The magic eye did not move (it was at 100%) and it took 20 minutes. the set did not revert to the previous level.
I turned up the second set and, guess what ? The second set behaves like the first one. §But the variation in level is less, and the time is shorter. About 10 minutes.
As many Grundig sets share a very similar radio part, you may have a clue ;-) or at least a lead to follow...
I, for one, will let the two sets as they are. For now I'm not going to do radio repair for some days... Maybe a recent bad experience ? Who knows :-;
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