Wanted: Cheap receiver/amp
I have been using a 2x50w receiver for years for downstairs, and it burned out. I tried replacing its internal fuse, but it immediately blows again. I'm guessing some circuitry or something is fried, and I don't think it's worth paying to get fixed.
What I need is a cheap 2x100w (or 50, but I have 100w speakers) receiver. 2 or 3 inputs would be optimal, but I can easily get a splitter to add more.
A/V or surround is not needed, or even wanted really. Just 2 (or 2x2, I guess) channels) - there's already a 5.1 system down there)
Would it be smarter to try to fix it myself? Or maybe just sell the speakers (I probably can't get much for them anymore, though... I paid $75/ea. originally)?
Edit: Actually, does anyone have any suggestions to fix it? I think I'd much rather try that...
What I need is a cheap 2x100w (or 50, but I have 100w speakers) receiver. 2 or 3 inputs would be optimal, but I can easily get a splitter to add more.
A/V or surround is not needed, or even wanted really. Just 2 (or 2x2, I guess) channels) - there's already a 5.1 system down there)
Would it be smarter to try to fix it myself? Or maybe just sell the speakers (I probably can't get much for them anymore, though... I paid $75/ea. originally)?
Edit: Actually, does anyone have any suggestions to fix it? I think I'd much rather try that...
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Comments
If it is you've just fixed it for <$20 and if not you've just invested that much more to a dead piece of equipment.
Here's a link to the YouSendIt page, since it was too big for Imageshack.
http://s42.yousendit.com/d.aspx?id=33UXFA49ZLKIC0OUSJJY8MR88
Replace those 4 FET's (field effect transistor) and you might have a working amp again.
Make sure to keep the little plastic pieces to put in between the transistors and the sink if there are any and use cheap white thermal paste not AS3 or AS5 as it could short them together.
Good luck!
Good luck, entropy.
One last question: where would I get these?
Should I take the whole board out and then take them off, or no? I know my around a computer, but that doesn't mean I understand what every little trace does
Edit: So basically I need a babystep-by-babystep guide from you... if you're willing. Otherwise if you know of a site, that'd be great. Or I could just trash it :P
Before pulling them out make a note on the sink (such as 1, 2, 3, 4) over each FET and a coresponding note on the FET so that they go back in the proper location. The FET's have the model number on them, try rat-shack for them and if not look for a good electronics supply house such as ECS (no not that ECS).
How should I go about desoldering those things? I don't want to poke around where they were originally solders, as I'm terrible at it. I know I'll melt it too much and it'll spill over some other traces and ruin it all anyway. Can I just snip those legs, then snip bits of the new transistor's legs off and solder them there? Or what?
Also: that white pad. What should I do with it? Why do I even need it? And you say use some cheap thermal paste? Why not AS%? I've also got some Radioshack-branded "Silicone-based Heat Sink Compound." Cheap enough?
Oh, is there any test I can do with a multimeter or something to test if it is in fact these transistors?
Uhhh... it looks like there might be burn mark on the underside... but I don't know.
I'm not familiar enough with testing the current flow through transistors to tell you how to test them but I do know they're basically a tri-mode diode, a base leg, a collector leg and an emitter leg and are available in n-p-n or p-n-p (n being negative and p being positive) and generally in a system such as that with a push pull amp circuit they're arranged with one n-p-n and one p-n-p on each channel.
But as to what I asked at first, where's the discoloration?
Sigh. All that work and it turns out I could just scrape away whatever it was
http://s53.yousendit.com/d.aspx?id=1LO5O58J0HYRR1222S6SIRLW8P
By "macro" I just meant little tiny things. I ended up doing exactly what you said, though
Works like a charm. Macro? We dun need no stinkin' Macro...
The transistors are to the right of the image and the top one is n-p-n.
If I had my handy-dandy compendium of arcane knowledge I could tell you a replacement part number but I lost all my parts catalogs.
Try Parts Express for replacement FET's, a pair of 50W transitors per side are likely what you're needing.
Yes I know your amp outputs 50w total and a pair of 50w transitors will net a total of 100w per channel but they build them like that to allow for peak output (50w is continuous rating) and to allow the transitors to supply the needed wattage for 4 speakers if using parallel wiring to 2 pairs of speakers.
At any rate, give replacing those 4 transistors a shot. If it fixes it you're in business and if not at least you've tried and learned someting for a few bucks invested.
If I were you I'd get on eBay and start shopping for power amps. You ought to be able to get a Crown D75 for a reasonable price.
-drasnor
Amp: 8 ohm min
I'd already checked on that. So when I desolder the FETs, if they're faulty, it should still work? It won't like, ruin other junk in there? I'm going to try to find some of that copper mesh stuff at work tonight (I work at a big hardware store)
The pre-amp won't care if there's no load as it is low voltage and current.
In case you haven't heard btw... be careful messing with circuits like this. I like to just use one hand so shocks can't go across the heart.
After you're done testing it, unplug the power cord and if it hasn't blown the fuse turn the power switch on and leave it set for a couple of days to help discharge the caps although caps can hold a charge for as much as a month.
EMT is right on the mark with the one handed advice. I was taught to work with one hand in my back pocket. High voltage can cause your muscles to clamp down and the idea behind having the hand in the pocket is that when you're swinging your arm around to knock the other loose you'll gain enough momentum to jar the hand loose when the free hand hits it.
It freakin' worked! I took my time, desoldered everything, set it back in and TA-FRICKIN'-DA, it doesn't blow! I let it sit for a few seconds to make sure and yep, nothing wrong with it! I'm so excited right now you have no idea. I've never done any circuit board work with ANYTHING, so this is a great feeling. Thank you so, so much.
I just need to find some replacements for those things, and then I should be good to go. Will generic radioshack thermal paste be good enough, or is there a specific, non-conductive kind I should buy?
Edit: It doesn't have a "switch" per say. More like a button that brings it out of standby. Should I do that, and then unplug it for a few days/a week?
It's fun working on something like that, I remember how I felt after my first tube amp mod (and those babies use 600v plus inside) I was just estatic when it all worked
There's absolutely nothing here... is there a place I can order some from?
You'll need parts numbers. I take it that theres no real electronics supply stores there...