TDA2822M Oscillatiing in Grundig Receiver

jff6791

Member
2016-02-03 8:06 pm
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.

John
 
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.
 

jff6791

Member
2016-02-03 8:06 pm
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.