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| Test Equipment Anonymous (TEA) group therapy thread |
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| Vince:
--- Quote from: mnementh on July 06, 2022, 05:12:22 pm --- --- Quote from: Vince on July 06, 2022, 04:04:32 pm ---TV REPAIR --- End quote --- So this panel is actually designed to be able to service the LED BL array...? HALLE-FUKKIN-LUJAH!!! These LED arrays are driven CC in series; they separate them in banks and modulate the drive current to different zones of the screen for higher "dynamic contrast" compared from one part of the screen to other parts. I'd guess that the two banks on each side drive alternately to be able to keep dwell time lower; either that, or each bank is aligned with a different diffraction lens so it corresponds to a different quadrant of the screen. :-// mnem --- End quote --- Well no, sorry to disappoint ! :-DD You must have misunderstood me.... it is just as unserviceable as the older TV I worked on. In both cases you have to crack the screen apart, peal every layer of the "sandwich", and disconnect and remove of course the LCD panel itself... which is the dangerous / tricky part. Also in both cases the strips are held with freaking double sided sticky tape which is a nightmare. This TV, is even worse because the strip is stuck against its heat sink, there is very limited access to get tools, unlike the older TV with the strips laying flat on the chassis, so you had ample access from all sides to pry the strips off of the chassis. So no, sorry Dragon... still a bunch of crap I am afraid ! :( I will call it serviceable when you can replace the strips without having ti remove / disturb the LCD panel. That is, put the strips OUTside the frame, not inside..... ::) ... and when the strips are also fixed with screw or any method designed to be easy to get off... so no glue or tape thanks... Of course this will never happen... at least not on consumer stuff... maybe professional fancy expensive screens are built better, I don't know... |
| Vince:
--- Quote from: Zoli on July 06, 2022, 04:14:38 pm --- --- Quote from: Vince on July 06, 2022, 04:04:32 pm ---TV REPAIR ... So now nee do a lot of scraping so I can test all the LED's in these two dead strips, and find the dead ones.... --- End quote --- If any of your multi-meters that would lit the LED's up, that would be a great help; especially if you have sharp tips, like the Pomona 6275 :-DD :-DD :-DD /enabling --- End quote --- Yes as I said these LEDs only drop 0.7V so I was able to test them with my Fluke 11 or any DMM just fine, no worries ! 8) So, I worked on the those remaining two defective strips. The 4th one, far right, found one open-circuit LED, bridged it, now strip works. :-+ Also found one that dropped only 0.5V when all the others drop a very consistent 0.77+ Volt. Strange.... maybe that particular LED is on its way out, who knows.... this repair is free and obviously comes with no guarantee ! :-DD Then I looked at the other string/strip, second from the left. One that was working before hmm... Checked all the LEDs... they were ALL good ?! :wtf: checked for bad connections between the LEDs, the connector at the end of the LED strip, then further, at the other end of the cable, where the power board plugs into... no joy, solid reliable connection. Hmmm... so I powered the TV to measure voltages. The working strip, first from the left gets 130V, the other one gets... 0V ?! But they are both wired in // on the power board, at the edge connector ! The two strips HAVE to have the same voltage ! :-// So... I guess only explanation would be a cracked solder joint on that connector on the power board ?! :-// Lemme check for that... |
| Zoli:
--- Quote from: Vince on July 06, 2022, 05:31:09 pm --- --- Quote from: Zoli on July 06, 2022, 04:14:38 pm --- --- Quote from: Vince on July 06, 2022, 04:04:32 pm ---TV REPAIR ... So now nee do a lot of scraping so I can test all the LED's in these two dead strips, and find the dead ones.... --- End quote --- If any of your multi-meters that would lit the LED's up, that would be a great help; especially if you have sharp tips, like the Pomona 6275 :-DD :-DD :-DD /enabling --- End quote --- Yes as I said these LEDs only drop 0.7V so I was able to test them with my Fluke 11 or any DMM just fine, no worries ! 8) So, I worked on the those remaining two defective strips. The 4th one, far right, found one open-circuit LED, bridged it, now strip works. :-+ Also found one that dropped only 0.5V when all the others drop a very consistent 0.77+ Volt. Strange.... maybe that particular LED is on its way out, who knows.... this repair is free and obviously comes with no guarantee ! :-DD Then I looked at the other string/strip, second from the left. One that was working before hmm... Checked all the LEDs... they were ALL good ?! :wtf: checked for bad connections between the LEDs, the connector at the end of the LED strip, then further, at the other end of the cable, where the power board plugs into... no joy, solid reliable connection. Hmmm... so I powered the TV to measure voltages. The working strip, first from the left gets 130V, the other one gets... 0V ?! But they are both wired in // on the power board, at the edge connector ! The two strips HAVE to have the same voltage ! :-// So... I guess only explanation would be a cracked solder joint on that connector on the power board ?! :-// Lemme check for that... --- End quote --- 0.7V is the protection anti-parallel diode is what you've checking; if the LED doesn't lit up, is bad. And the white LED working voltage is over 3V, no exceptions, but most of them lit up just over 2.4V. So, start checking your multi meters, which one has over 2.5V for diode testing, then redo the checking. |
| Vince:
--- Quote from: Zoli on July 06, 2022, 05:45:32 pm --- --- Quote from: Vince on July 06, 2022, 05:31:09 pm --- --- Quote from: Zoli on July 06, 2022, 04:14:38 pm --- --- Quote from: Vince on July 06, 2022, 04:04:32 pm ---TV REPAIR ... So now nee do a lot of scraping so I can test all the LED's in these two dead strips, and find the dead ones.... --- End quote --- If any of your multi-meters that would lit the LED's up, that would be a great help; especially if you have sharp tips, like the Pomona 6275 :-DD :-DD :-DD /enabling --- End quote --- Yes as I said these LEDs only drop 0.7V so I was able to test them with my Fluke 11 or any DMM just fine, no worries ! 8) --- End quote --- 0.7V is the protection anti-parallel diode is what you've checking; if the LED doesn't lit up, is bad. And the white LED working voltage is over 3V, no exceptions, but most of them lit up just over 2.4V. So, start checking your multi meters, which one has over 2.5V for diode testing, then redo the checking. --- End quote --- Oh OK ! Didn't know about this built-in protection diode ! :-// Thanks for that... makes more sense now... Still, it does not explain why that bad string can have zero voltage when it's in // with the other one tat gets 1230V.... I just checked the solder joints of the connector on the power board, they looked good. Reflowed them anyway, still no joy. Makes no sense. See picture below. There big fat traces on that connect pins 1 and 3 and 2 and 4 to // the strings. How can have 130V on a set of pins and zero (well, 1.5V right now.. better than nothing I guess !) on the other set of pins.... Think I will just bridge those pins myself to make sure they are really connected... As for DMM's, I don't have fancy modern ones that can test white LEDs. When I checked the LEDs in that older TV last time, what I did was simply use my lab power supply, plenty of voltage there... I do have sharp / SMD probes, helps a lot getting good connections when testing the LEDs after having scraped the white solder mask.... Cheap Ebay probes but they work just fine.... |
| Vince:
OK I tested again all the LEDs in that string, this time with my lab supply... I can light them up white now, so I am 100% sure they work.... and they do, all of them. |
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