 Posted: Tue Nov 24, 2009 9:43 am Post subject: |
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You're welcome.  |
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| Posted: Tue Nov 24, 2009 6:51 am Post subject: |
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| SUCCESS! Replaced all 3 of those capacitors, the store I went to had exactly the same values as I pulled out. Soldered them in, buttoned everything up for a test, hooked up the oscilloscope, and plugged it in. At first, my heart sank. The same exact thing - sawtooth. But it was strange: it was a lot faster an oscillation than usual, practically straight-up, straight-down, like it knew exactly what it was doing. I let it sit for a minute doing the sawtooth, unplugged it, watched it discharge, then I realized... what if having the chopper transistor removed was preventing the circuit from working right? I had kept that out because I didn't want the TV firing up with the board sitting on its side. Well, I fired up the soldering iron, mounted the big clunker chip back in place, soldered it down, and prepped for another run. Plugged it in, and... SMOOTH LINE! Voltage shot up and kept flat even at 12 volts. Heard a slight chirp from the board as well as it spring back to life. VICTORY! And just in time for my grand plan, too. Spent the next half hour putting the panels back in place, screwing the board down, moving the wires to their proper places. After I got the board mounted, I hit the power button. I have never been so happy to hear the sound of TV static in my whole life.  (although I do wish this model had a blue-screen "video mute"...)  Grand plan? Put the TV all back together, clean up the area a little, and wait for the roommate (the owner of the TV) to get back home. The power button's always been missing from the front panel, so with the TV all put back together, when he gets home, I'd be totally unexcited, and say "Well, I got one thing working...". He'll see the power button (which I "melted" back into place on the front panel - it was floating around inside after it broke off) and push it. And the TV will spring to life with the computer looping his favorite song. This, my friends, will be a night to remember. THANK YOU SO MUCH, jts1957!! |
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| Posted: Mon Nov 23, 2009 4:48 am Post subject: |
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| With that in mind (good value but bad ESR) then it's settled, I'm just gonna replace all 3 of 'em So I'll try and grab the same values for everything but if they only have a step up higher voltage that's about the same size, I'll grab that instead. There's a bit of wiggle room in that area of the board so I shouldn't have much trouble as long as I stay within a few MM... What's funny is that I'm basically saving my roommate a few hundred bucks of repairs (more than the value of the TV of course) and it's like "did you fix it? is it working yet? hmm hmm?"... he keeps thinking he could get it fixed quicker than I can. Seeing how close to the solution I am... I don't even WANT to let it go! Even if he doesn't pay me back for the parts & work, it's well worth the experience, IMO... |
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| Posted: Mon Nov 23, 2009 3:45 am Post subject: |
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| O.K. to go 1 or 2 "steps" up in voltage (if the lytic can physically fit), I'd try to stay with the SAME value though. Remember, electrolytic have 4 main failure modes (five, if you include "bulging"), bad Value and ESR being the most common defects. Dielectric absorption (DA) and Leakage are less common failures. For example, a defective lytic CAN have Good value but bad ESR.  |
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| Posted: Mon Nov 23, 2009 3:33 am Post subject: |
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Bleh, looks like this is one of those times when the edit button "goes". Maybe it's a forum permissions configuration issue.  Anyway, meant to edit that it's a 500uF meter, not 700. Innywho... I pulled out C4108 (nasty bugger, right between a surface-mount capacitor) and it tested 47.1-48 uF (is it more proper to write "mfd"?). Went back and re-checked C4104 and rechecked it once more... still no result on it. I've got a good feeling that's the problem, although it's kinda an odd problem to have that be the cause of all this headache  I'm almost thinking since capacitors are so cheap, I should replace them anyway. But being as though it is a mere parts store, I probably won't be able to find the exact value. Is it better to substitute a higher voltage (so I've heard)? Is that acceptable in this case? Or is a higher rating better? Of course, it also begs the question: if a higher can be substituted, is that "better" at all, or should the original ratings always be stuck with? |
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| Posted: Mon Nov 23, 2009 3:21 am Post subject: |
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| Huh, well, here's the results I've got so far. C4104 (50v/15uF) wouldn't pull up a reading on my (up to 700uF) meter. It hung it every time I plugged it in, and gave weird readings if I had it plugged in while I turned it on (the instructions were kinda vague on how to use it...). Wasn't able to get a reading on it at all, let alone in the ball park. I'm looking at that one as my faulty component... even though it looks 100% OK... it's strange that it wouldn't test. C4102 (100v/2.2uF) tested at 2.17 uF. Don't think that's the one to blame but if I find a replacement at the store, I'll buy it anyway. I'm going to pull out C4108 next and see how it looks. But that C4104 has got me thinking... |
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| Posted: Sun Nov 22, 2009 12:43 pm Post subject: |
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| The indiscriminate replacing of parts just cause they're "in the same area/circuit." |
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| Posted: Sun Nov 22, 2009 12:25 pm Post subject: |
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As for the part, well, one of two dumb late-night things I did was a little screwed up. One, I bought a new replacement for that 35v/470uF capacitor. But I installed it backwards like a dang moron. Bulged it out and I promptly caught my mistake. But the reason it got enough power to blow up like that was because, as the service manual suggested, I tried giving it just flat 12v regulated power to see what the chip did. Evidently, it blew out. But I tested nearly every component after I made that dumb move (mostly resistors) and they seemed to be OK, no other overheated components or burns elsewhere... Not much else to do until the parts store opens on Monday though... I'll probably yank and test those caps tomorrow though.  |
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| Posted: Sun Nov 22, 2009 12:02 pm Post subject: |
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| From a quick look at some of your posts, seems like you are more heavily into computer/computer monitors rather than television. I'm just the reverse, with computers being my weakest (but still learning). Any parts catalog/site should have the required electrolytics. Get the supply running again before "shotgunning." Also remember, when a part is destroyed during troubleshooting, you then may have more than "the usual suspects" to check. Stick around here long enough and you'll also discover some other peculiararities on this forum ("edit" button comes and goes and can't search back more than one page on "unanswered posts," to name two). |
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| Posted: Sun Nov 22, 2009 11:26 am Post subject: |
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| Wow - THANKS for the useful reply!! So glad to have a direction! Those high failure item locations you mentioned, I hadn't even looked at as potential issues. I was probably looking in all the wrong places! Since it's so unlikely that RCA even exists as a parts-distributor anymore, can those components safely be replaced with "generic" alternatives of the same rating? Particularly the C4102/4104 capacitors? Also, C4116 and C4118 are past the transformer on the low (currently dead) side. Would it be worthwhile to replace these as well, even if they were working fine before this failure? If so, what should they be replaced with? And yeah, my roommate just had a total drunken blow-out over the broken TV (it's his TV and he sort of almost not-really half-blames me for unplugging it and breaking it...). The quicker I can get the parts, the better for the fabric of the universe |
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