Eddie3
Member
Last Activity: 03-02-2024, 05:14 PM
Joined: 10-19-2015
Location: Orlando, Florida
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Found another bad cap C10 (marked 470uf 16v) measured 47.36uf, esr = 136.7 0hms, Vloss = 98.1% and bad R44, with board discoloration (burns) and a lifted pad on R44. R44 measured 47 ohms (marked 10 ohms +- 1%). R44 is across C10, and the lifted pad also connects to D7. Looks like it got hot near K2. D7 and D41 are good. -
Saw the under side had to much light…this pic is better....
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Thanks. I've started at the 120V input side. Beginning with testing the electrolytic caps:
C4 680uf 25v ( Jamicon )
tested bad
158.6uf
Vloss= 19.9%
ESR= 4.95 ohms
C3 680uf 25v ( Jamicon )
tested ok
569.1uf
Vloss= 1.7%
ESR= 0.02 ohms
C19 1000uf 25v (Gemcon)
tested ok
973.8uf
Vloss= 2.1%
ESR= 0.02 ohms
diodes D1 thru D5 tested ok...Leave a comment:
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A schematic diagram would be helpful; like to see what point can cause failure for the optoisolator .Leave a comment:
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Tripp-lite SMART1000LCD not charging, no emergency power!
I have opened up the case and saw no visible parts / board damage. Initially I removed the battery; measured about 9V. Then I had put it on trickle charge until it got charged to 12v, but problem persisted when I put the battery back. It appears my Smart1000LCD UPS will turn on but it will not charge the single 12v 7AH battery, nor operate in emergency mode. It lights up when powered on, but I’m unable to power test the device (holding power and Speaker button simultaneously).
Took voltage measurements of battery:
charge mode: 11.8 DC Volts (in unit)
battery backup... -
Re: Samsung UN50NU6900FXZA
I apologize for not responding sooner; and thank you for suggesting to check the bridge rectifier firstly, by cutting leg(s).
However, the problem was finally resolved when I bought a used compatible board:
BN96-48456A.
I was pleasantly surprised when the backlight came on and the setup started by the TV talking to me. Ha!
I then slapped the back panel back, attached stands, updated the firmware and tested for functionality. Everything works.
Thank you all very much...Leave a comment:
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Re: Samsung UN50NU6900FXZA
Appreciate your suggestions. I really wish I had a schematic diagram, so that I could read directly from it as to what the part number of that MOSFET actually is. But I am hopeful that it didn't burn off the labeling, unless Samsung is using an unlabeled, proprietary MOSFETs in their TVs.
...
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Re: Samsung UN50NU6900FXZA
The main box is connected to a panel of several circuit breakers and TV is usually connected to the 15A breaker. But I think you're absolutely right about using a surge protector/suppressor on the TV.
No, not yet on the bridge (8 solder points) because I'm still haven't finished getting out the MOSFET (6 solder points). It's been difficult because circuit board is double-sided.
I bet you guys (who work on these TVs eryday) use those Electronic Desoldering Vacuum pump device for component removals.
...Leave a comment:
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Re: Samsung UN50NU6900FXZA
Thanks for taking the time to explain that. I had a feeling it was associated with the power going out and coming back on. Will have to make sure it's protected with a good surge protector....Leave a comment:
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Re: Samsung UN50NU6900FXZA
Your English is fine and I should have checked again when you mentioned it. I will have another look, because I thought I had seen a few black surface mounted components near that MOSFET.
I'm starting to wonder what might have caused that MOSFET and/or bridge rectifier to fail? Because I would be very disappointed if these components were replaced and then later, burn out again.
Thanks...Leave a comment:
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Re: Samsung UN50NU6900FXZA
Thank you for your suggestions and I should have checked the varistor first because I needed to unsolder the one pad to lift that leg !!
but what are the sense resistors, please?...Leave a comment:
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Re: Samsung UN50NU6900FXZA
Thank you for your comment....Leave a comment:
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Re: Samsung UN50NU6900FXZA
Thanks for the suggestions; I finally got the circuit board out and thought I'd get to the MOSFET “QP801CS” which has not been very easy with my 30 watt iron. It has 6 pins, if you count the 3 extra “heat sink posts” soldered into the board.
The Bridge rectifier “BD801S” has 4 pins, plus 4 more soldered points that hold the metal heat sink to it, for a total of eight. Was saving this for last.
Haven't lifted one leg of the varistor “VX801X” to test it out of circuit yet.
Fuse...Leave a comment:
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Re: Samsung UN50NU6900FXZA
Sorry but I could not add this picture via edit. It shows the varistor and BRIDGE RECTIFER device....Leave a comment:
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Re: Samsung UN50NU6900FXZA
Not sure if this is an MOV, but it read 7.8 Megohms. Don't think it's blown.
Not sure how the rectifier is in the circuit because I haven't seen the bottom, nor any schematic diagram (wish I had one). In-circuit testing shows short between 1 and 4, the outer ends, both ways. All others show reverse bias voltage measured both ways. Seems like a bad, situation?
I still haven't had a chance to remove the board but was starting to think maybe I should consider shotgunning the thing, picking up a salvaged board....Leave a comment:
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Re: Samsung UN50NU6900FXZA
Thanks for that link; I'll try that when I get the chance....Leave a comment:
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Re: Samsung UN50NU6900FXZA
Thank you for your reply; I saw what looked like a threaded screw (bottom end) on that large heat sink.
I had such a heck of a time getting the cover off (no screws on back cover) and was so disappointed with that! I worry that I might damage the board by removing it due to the fact it is also attached without screws.
I will try to remove it and check it out, and will be inspecting the bottom for arcing marks or burnt traces / components.
Will try to post some pictures of the underside and...Leave a comment:
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Samsung UN50NU6900FXZA
I have a no power, no standby with BN96-49483A Main Board Power Supply for the UN50NU6900FXZA Samsung TV. It appears this is an All-In-One Main Board.
Upon a visual inspection, the fuse is blown, there is a burnt blue cap that is close to a heavily coated (silicone or conformal coated) power transistor. In-circuit testing with meter revealed shorts between all three terminals of that transistor (No reverse bias voltage). The burnt blue cap (marked R 221k 1kv) measures 137.9uf with 0.33 ohms (esr).
Is it possible to repair board by replacing just these 3 components,... -
Re: New Members - please post your introductions here
Last edited by Eddie3; 08-17-2021, 08:52 PM. Reason: Forgot that I had already introduced myself! :)Leave a comment:
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Re: New Members - please post your introductions here
Hi, I'm a computer tech with a background in Electronics Engineering. I enjoy repairing (or at the least the challenge of repairing) computers, laptops, smart phones, large appliances, and other electronic devices. These forums are especially enjoyable to read and I like helping people. Hopefully I can get help when troubleshooting s problem.Leave a comment:
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