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 Post subject: VEF 202 - bad sound
PostPosted: 17 Aug 2020, 18:27 
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Joined: 03 May 2011, 15:16
Posts: 188
Location: Romania,Iasi City
Hello everyone!

I have at home two old USSR radios VEF 202. One is from a friend and the other one from a neighbour.
The first one works very fine on every band now and I replaced the contacts from the battery case too and the electrolityc capacitors.

The second works, but it makes a bad noise on the low part of the medium waves a strong whistle and also the same whistle is appearing while receiving any station on medium waves. Also, the local station sounds distorted and sometimes even during the night the same problem happens to the other stations. When I tested the audio amplifier as an auxiliar, the sound is good. Where should I look for the problem?
P.S: At this radio I haven't replaced any capacitor yet.. but I don't know exactly if the cause of whistle is this.

Here is the diagram:
Image


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 Post subject: Re: VEF 202 - bad sound
PostPosted: 17 Aug 2020, 18:38 
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Joined: 03 May 2011, 15:16
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Location: Romania,Iasi City
https://player.vimeo.com/video/448634967?utm_source=email&utm_medium=vimeo-cliptranscode-201504&utm_campaign=29220


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 Post subject: Re: VEF 202 - bad sound
PostPosted: 17 Aug 2020, 21:54 
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Joined: 04 Jun 2008, 20:59
Posts: 4256
Location: Arizona, USA
Hi, Usually that sort of behavior indicates that the intermediate frequency (IF) stages are out of alignment. This can be because of drift in capacitors that are used with the coils to tune obtain the correct center frequency and bandwidth. The RF stage and main frequency tuning circuits can also cause this. It if occurs on only one band then I would check the components for that part of the antenna circuit first. It is all bands then I would more strongly suspect the IF amplifiers or the RF oscillator. You really need a servicing guide on it and some test gear to be sure.

My personal experience with similar problems has been when someone before me messed with the coils and trimmers and screwed it up. YMMV

Good listening
Bruce

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 Post subject: Re: VEF 202 - bad sound
PostPosted: 18 Aug 2020, 02:47 
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Joined: 03 May 2011, 15:16
Posts: 188
Location: Romania,Iasi City
If we try to rotate clockwise or anti-clockwise just a quarter of a rotation on some coils (from the detection to the earlier) and then again to their initial position, we lose the amplify, but the problem persists.
I guess that the problem comes from the AGC. From L37 through T2 (MP40) and the diode from its base and also the capacitor of 50nF from the T2's collector through the base of T1.


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 Post subject: Re: VEF 202 - bad sound
PostPosted: 26 Aug 2020, 06:19 
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Joined: 03 May 2011, 15:16
Posts: 188
Location: Romania,Iasi City
I solved the problem by replacing C60 and then I replaced the others electrolytics.


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 Post subject: Re: VEF 202 - bad sound
PostPosted: 21 Sep 2020, 12:22 
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Joined: 18 Sep 2018, 01:15
Posts: 22
Quote:
The second works, but it makes a bad noise on the low part of the medium waves a strong whistle and also the same whistle is appearing while receiving any station on medium waves. Also, the local station sounds distorted and sometimes even during the night the same problem happens to the other stations. When I tested the audio amplifier as an auxiliar, the sound is good. Where should I look for the problem?


the whistle comes from a bad capacitor C84
but I would like to make sure that the rest are working, if not everything has changed then this is a problem
I have repaired these receivers ~ 1000 pieces


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