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kbs1
Senior Member
Last Activity: 01-09-2016, 08:56 AM
Joined: 02-16-2012
Location: Bratislava, Slovakia
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  • kbs1
    replied to Whole inverter measures 675 ohms
    in Troubleshooting TVs and Video Sources
    Re: Whole inverter measures 675 ohms

    Woohoo, it works!! ) It was not an inverter problem after all, just the OLD iverter in some way shorted 1,5 years later ;-) I just cut the trace that still went AFTER the fuse to the old iverter section and its parts (bottom side of the board / upper side was desoldered to make room for new inverter). Now the fuse goes directly to the chinese inverter only, old inverter remains are now completely cut off (that's the ones that blew the fuse). Works like a charm!
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  • kbs1
    started a topic Whole inverter measures 675 ohms
    in Troubleshooting TVs and Video Sources

    Whole inverter measures 675 ohms

    What is shorted? It keeps blowing 3.15A 175V inverter fuse. I have already replaced the original inverter on the board (samsung monitor T220 - 22 inch) with this exact china one a year and a half ago: [url]http://www.ebay.com/itm/281363783165[/url]

    I desoldered all of the original inverter parts, drilled the board and then soldered +, ground, on/off and dim signals to feed this new inverter. Then attached the new inverted onto the board and fit snugly in metal casing of the monitor.

    Worked flawlessly but now it just keeps blowing the fuse. New one is on the way but...
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    Hello guys, sorry to revive an old topic, maybe I should establish a new one. But long story short, I've geared up in terms of equipment and some troubleshooting knowledge.

    Gear:
    + 20mhz oscilloscope
    + much better soldering iron
    + good LCR meter

    Now using this and some great help on EEVBlog forum, we have finally checked all the
    * diodes (good)
    * caps (desoldered, checked, good, visually good)
    * transistors (not shorted)
    * mosfets (not shorted)
    ...
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    Last edited by kbs1; 09-17-2012, 05:32 AM.

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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    What about this?

    [url]http://www.ebay.co.uk/itm/Replacement-Inverter-Wiring-Switch-CCFL-Neons-/230363518011[/url]

    Would I be able to test my lamps with this?Re: iiyama ProLite X486S dead - psu ...mps with this?Re: iiyama ProLite X486S dead - psu / inverter issue

    What about this?
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    Also, T901 is shorted on one side (the "f902" side). I traced the PCB leads and think that shown contacts are not connected by any direct PCB lead. They measure 0 ohms. The other side is always out of range even on 2000K multimeter setting. Also any other pin combination is also always out of range. Maybe this is normal, if not let me know
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    As far as the "faint blue led" problem goes, the LED does not work at all now. Only the orange standby does. The voltage on BLUE led is 2.24V when ON, 0V when Off. Voltage on orange LED is 1.84V when Off (standby), 0V when ON.

    Why is this voltage difference present? Is it because the led had burnt out? I don't care about the led, just wondering if it has something to do with the general backlight problem.

    Thanks
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    So guys, after a long research & parts availability checking I have replaced AP2761I-A with STP12NM50FP, and also of course replaced fuse F901. The monitor now "works", so it works like before - no backlight at all. I have also found & resoldered another two dry joints on the board, this time on the far side (the F902 side of the circiut) of T901 (big ?transformer?).

    What should I check next? The IC901 voltages are correctly measured the last time I did it (before Q903 was shorted).
    ...
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    I'll do that, but first I need to get my hands on Q903 (totally shorted). It is not available in any local shops, they said they might have replacements for it but I did not have time to personally go to the mentioned shops recently (too much work & school). I'll try to visit the stores next week, and if I don't find any suitable replacement (or if the replacement will be expensive), I'll order a few pieces off ebay (2$ postage, 2 pieces - 4$, total 6$, approx 4.2€ - fine). I'm also planning to buy a new multimeter capable...
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    Desoldered Q903, shorted. No other parts show as shorted on the circuit at this time. Did not desolder anything else at this point. I'm going to replace the transistor. Do you think it's enough or should I desolder something else (like DB901) and test it out?
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    Damn that's a really good idea Why couldn't I think of that sooner? Anyway three parts are about to be desoldered today and measured (maybe tomorrow if I'll run out of time). I'll let you know what I find
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    Thanks that is a nice video. I will desolder the rectifier, main capacitor and main transistor tomorrow and try to test them.
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    well at least Q903 (big transistor near big capacitor) is nicely shorted.
    D-G 16ohms
    D-S 0ohms
    G-S 16ohms

    Also main Rubycon capacitor shows 1.5ohms (shorted), but I think it's the transistors fault (same leads and whatnot)

    Also DB901 shows shorted on pins 1-4 but again, it's the same PCB leads as the C905 is hooked onto.

    From your personal experience, which part is faulty? Is it the transistor? What does blow up most commonly first (other than the fuse)? When I...
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    Bought new F901, soldered, plugged in, instant burnout of the same fuse. What could be wrong?
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    While I sort this out, I remember the readings (I was just verifying them when the fuse blew out), so here goes:

    CCFLs connected, logic board connected, LCD panel disconnected:

    2) What is the DC voltage for pin 3?
    standby - 14.95V
    monitor on - 16.92V

    3) What is the DC voltage for pin 7?
    standby - 12.04V
    monitor on - 13.36V

    4) What is the DC voltage for pin 5?
    standby - 1.04V
    monitor on - 1.05V

    Also, the...
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    Hello guys, thanks for the help, buf F901 had blown out.. blowing fuses in our entire home on the way out. I guess my hand must have slipped and connected pins 7-8 or 7-6 or something like that, causing an electrical short. Those IC901 contacts are so tiny, that it's really hard to control your hand like that ulness your are a surgeon

    I have checked all the 8-leg Q's on the board, they are still OK, nothing else seems to have blown out (only the fuse smells bad & is blown). So give me a little time, I'm going...
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    CCFLs disconnected, everything else connected:

    2) What is the DC voltage for pin 3?
    standby - 14.95V
    monitor on - 16.92V

    3) What is the DC voltage for pin 7?
    standby - 12.04V
    monitor on - 14.07V

    4) What ohms reading did you get for fuse F902?
    0 ohms, 0.5 to be exact
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    Hi, I have tested the mofsets and values were always out of range. I also tried to test things like "S2-G1" just to be sure, always out of range. So they seem good. Previously I have done this test, and the results were the same.

    5) the number is
    SG6841SZ
    KA497280603Q

    It is really hard to read, so just in case I got it wrong here is a photo of it (I had no chance to read it using bare eye or using magnifier ;-)...
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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    Hello, did the tests:
    1) wallpaper shows up, forever, visible only using flashlight

    2) faint blue, should be strong blue (the led is so faint, that when the monitor is assembled, the led is invisible through plastic cover)
    "a) does it change color at any point?"
    - no, only when I disconnect the signal cable and monitor goes to standby, in that case it is strong orange (as it's supposed to be, visible through plastic when assembled)

    3) no, at all, no flash, nothing...
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    Last edited by kbs1; 02-19-2012, 06:58 AM.

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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    According to [url]https://www.badcaps.net/forum/showthread.php?t=8598[/url] , I have tested all the small signalling transistors and other 3-legged small components (marked D...) for shorts - none found. I have also tested all diodes - one of them did give me a short circuit beep for a split second - then resistance started to grow. Is this normal? Do they need time to "start up"? The longer I "charged" the diode the longer it beeped when I reversed the multimeter leads - multimeter beeps and shows negative...
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    Last edited by kbs1; 02-18-2012, 06:37 PM.

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  • kbs1
    replied to iiyama ProLite X486S dead - psu / inverter issue
    in Troubleshooting Computer Displays
    Re: iiyama ProLite X486S dead - psu / inverter issue

    I have taken out the logic board for the first time today - previously I have looked under it and there was nothing - only one rubber pad but no components. This turns out to be true - all components are on the front of the board. I have also checked all solder joints on the back now - seem fine. Pictures of the back side of the board attached.

    I'd love if someone could came up with some new ideas on what to test. So far at this moment, I'm dry Regarding the capacitor possible problem, is there any way I can...
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    Last edited by kbs1; 02-18-2012, 06:00 PM.

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