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Rebuilding stereo, need some1 handy with circuit boards!


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#1
Mariaeehhh

Mariaeehhh

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This is shelf system radio. 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!

Edited by Mariaeehhh, 11 June 2009 - 06:25 AM.

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#2
ZedU54

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...I used to work on this kind of stuff all the time. However, without more information, any help I could give you is going to be very limited. Since you're trying this in the first place, I have to assume that you at least know a little something about electronics...
...First, where did find your information (so I can also look for some)? Did you Google the model number or something? Was there anything you found that included a schematic diagram of the set (which would be the absolutely most valuable information you could find; even though you might not be able to make the least bit of sense out of it, it would help me greatly in trying to help you)?
...Next, what is Q401? That is, what is it supposed to do in the set (if your source of information said anything about that)? And what was the original type number on it? If it is some type of voltage regulator (which I'm beginning to suspect) you're probably not going to be able to replace it with just any NPN silicon transistor and have it work. They tend to be somewhat critical in that kind of application (which is why the NTE382 was specified for it). Also, there can be other components in that regulator circuit (especially a zener diode) that may have failed, so even if you do replace the transistor, it still won't work.
...Also, did Q401 have any kind of heat sink on it? It is common to see some discoloration on a printed circuit board around a component that runs hot (and sometimes they do; that's why they have heat sinks on them)...
...And finally, use a reasonable amount of care when soldering on a circuit board, especially if it is not your area of expertise. It is not hard to damage one from too much soldering...I've done it myself a few times, even after years of experience...

...also, this really isn't the right place for this topic, as it has nothing to do with building/upgrading computers... :)

...educated guess, but perhaps 'Off-Topic' or 'Geek Talk' is probably a better place for it...

Edited by ZedU54, 11 June 2009 - 10:13 PM.

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