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Only hear a buzzing sound...

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Rs 2640 stereo system after five years suddenly stopped working. On all of the sources (fm Radio,am Radio, cd player, tape player) it just produced a buzzing noise. I looked this up and it seems to be a common problem with these units. There was ONE suggestion that apparently worked for a few people, and that was to replace the q401 transistor with an NTE382. When I took it apart and looked at the circuit board, the Q401 seemed to have had a darkened area around it, like a little explosion occured. Anyways, I tried replacing it (not with an NTE382) with a 2n3904 and the radio didn't even turn on, so then I tried a 2n3906 and the radio turned on but now with no sound at all, but when I turned it off the speakers made like backfire noise, now I purchased a few more npn silicone transistors on hopes this might fix my problem, should I even try these? Or just order the NTE382 online (I got the rest of them at RadioShack) or am I just wasting my time? I have never worked on a circuit board before, I'm just a poor 22 year old bartender who doesn't want to afford a new radio so any instructions might need to be broken down sort of specifically for me. But honestly, I'm finding this a super fun project. The soldering at least makes it all worth while, haha. Thanks!
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    Portlock - Oahu

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You're braver than most people are without experience! Kudos to you! :)

The 2N3904 is a "low power" NPN transistor while the 2N3906 is a low power PNP transistor. Basically, these two are not interchangeable because of their junctions. They are opposite polarity and when you put the 2N3906 in place, it probably shorted VCC (or drive circuit) to ground... thus the pop. The NTE382 is a higher power NPN transistor so using the 2N3904 (NPN) wouldn't have fixed your problem either

I know nothing about your radio, but given the NTE382 is an audio transistor, it's probably in some kind of push-pull configuration. I may be wrong. Do you have a schematic of the radio handy? In your research, did you run across a schematic someone posted somewhere?

Edited by makai, 17 July 2009 - 01:59 AM.

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