TDA2822M Oscillatiing in Grundig Receiver - diyAudio
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Old 3rd February 2016, 07:56 PM   #1
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Join Date: Feb 2016
Default TDA2822M Oscillatiing in Grundig Receiver

I"m troubleshooting a grundig SW receiver with a low frequency output oscillation that's using a TDA2822M chip in bridge mode. The problem goes away with headphones plugged in and also with a 100 ohm resistor in series with speaker. Have subbed out the chip and bypass/filter caps in circuit as well as 8 ohm speaker. No luck. Any thoughts appreciated.

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Old 7th February 2016, 04:24 PM   #2
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Join Date: Nov 2004
Location: Germany
Grundig, TDA2822M? Probably a Chinese-built "Grundig" model then (rebadged Tecsun or something)?

Anyway, low-frequency oscillation sounds like you should turn your attention to power supply decoupling. I guess you'll find a few bad electrolytics with sky-high ESR. (Got something resembling a makeshift ESR meter?) Also check whether the voltage regulator still does its job.
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Old 7th February 2016, 04:43 PM   #3
nec3 is offline nec3  Turkey
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Location: Ankara
Is the receiver operated on batteries or AC mains ?
It oscillates also in low volume levels or only when turned up max ?
What is DC voltage at the input and output of 2822M ?
When you short inputs to the ground, the oscillation stops?
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Old 12th February 2016, 10:53 PM   #4
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Thanks for those suggestions. The radio is branded Grundig/Eton S350. I had never run it on batteries but when I tried that - problem gone. So I opened up the wall wart and there is no regulator in there or inside radio either - just some large electrolytics which I had already replaced. I was getting 8-10 volts out the supply even tho it's nameplate ssys 6 - have never seen that before. Swapped it out for a switch mode adjustable - set it for 6 volts and its back in business. Go figure.
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