Re: Proscan 55LC55S240v69
I went ahead and removed the mosfet and bench tested it and its good. There is definately something different between the boards as I still measure the resistance difference. I suspect they changed something to deal with the failure problems of this board. I think I am going to have to look for a replacement board and call it quits. It drives me crazy that its 95% there.
gsmy
Member
Last Activity: 11-05-2013, 08:05 AM
Joined: 05-01-2012
Location: Gainesville, FL
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Re: Proscan 55LC55S240v69
I desoldered the source pin to isolate it and retested and it shows open now between the source and gate. There must be some difference between the 2 boards.Leave a comment:
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Re: Proscan 55LC55S240v69
I went back over the board and tested the mosfets again, comparing the readings to the borrowed board. The 2 mosfets V805 & V806 that are next to the dc cap have different readings than the borrowed board. On my board they measure 15.5 ohms across the two outside pins for both, on the borrowed board they measure 78.7 ohms on the outside pins. The other pins measure open. Could this be bad mosfets or the difference between the different rated capacitor and possibly different transformer?Leave a comment:
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Re: Proscan 55LC55S240v69
My original board has a decal with the tv's model and serial number on it. The borrowed board does not, but it has a couple of other decals, one looks like it might be a revision or rebuilders decal. The transformer is a different number than the original and I think that may be why the cap is different as well. I am hesitant to swap the cap and dont see much point in swapping the transformer if I cant buy a replacement. I am going to check the mosfets again though. Can anybody recommend a good procedure for testing them?Leave a comment:
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Re: Proscan 55LC55S240v69
Yes I replaced the cap with the same value, did not have the other board at the time to notice it was different. Just wondering if anybody had an explanation as to why it would have changed and if there is any risk to damaging the borrowed capacitor.Leave a comment:
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Re: Proscan 55LC55S240v69
I tested the MOSFETS on the board and they checked out ok for shorts. I guess I will need to remove them from the board to do better testing.
When I got the tv, I recapped the psu. I also noticed at that time that the dc cap was bad and replaced it. I went over and tested everything else on the board and everything else checks out good. I did not remove the mosfets to test them completly though.Last edited by gsmy; 05-17-2012, 09:14 AM.Leave a comment:
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Re: Proscan 55LC55S240v69
I can, but dont want to burn up anything on the borrowed board.Leave a comment:
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Re: Proscan 55LC55S240v69
The original cap in my board is a CBB81 68nJ 1000v. I replaced it with this one.
[url]http://search.digikey.com/us/en/products/BFC238330683/BC1922-ND/502702[/url]
The borrowed board that appears to have been rebuilt has the CBB81 22nJ 2000v. Any explanation why it would be a different value?Re: Proscan 55LC55S240v69<br /> <br...> <br /> TheLeave a comment:
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Re: Proscan 55LC55S240v69
Went over all the solder joints on the transformer but it didnt change anything. I happened to look at the high voltage cap I originally replaced and compared the value to the other board and noticed it is different. The original cap is a CBB881 1000v 68nj but the other board has a CB881 2000v 22nj cap. I dont know if it would make a big difference or it has something to do with the different transformer. The numbers on the original transformer are different than the borrowed one.Leave a comment:
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Re: Proscan 55LC55S240v69
selldoor- in the smallest red circle is a component board number VD804Leave a comment:
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Re: Proscan 55LC55S240v69
I did replace all the capacitors that are listed in the kit. I will try to get a better picture of that area and will resolder all the pins on the transformer.
I dont have the other tv close by to try my psu in it. It was easier to remove the psu and leave the tv at his house. I can try mine when I take his back though.Leave a comment:
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Re: Proscan 55LC55S240v69
Interesting, The only cap that showed any damage was a high voltage cap next to the transformer (C857) and it had swelled and got hot on one end. I also ran across another post somewhere from someone else looking for the same capacitor for the same tv.Leave a comment:
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Re: Proscan 55LC55S240v69
The board number is T801. The other tv works as well. I dont follow on why I would try my non working psu in another tv?Leave a comment:
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Re: Proscan 55LC55S240v69
Its the large transformer on the power supply board. The borrowed psu came from one of the other 2 tvs and it looks like it was replaced at some point. With the borrowed psu installed in mine, the tv works perfect. I checked all the functions and inputs to make sure there wasnt any other problems.
So I was thinking about swapping the transformer to test but then I havent been able to find a replacement one available. So I am thinking its not worth the risk if I cant get another transformer even if it is bad.Leave a comment:
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Re: Proscan 55LC55S240v69
I considered it but dont want to take the chance and have 2 bad power supplies.Leave a comment:
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Re: Proscan 55LC55S240v69
I went over everything again including the diodes and everything I can test matches the borrowed psu. All the output voltages are good, the problem happens when the backlight is starting and the main transformer buzzes like its under a heavy load or short and then the backlights shut down. I am thinking its a bad transformer and it looks like the one on the borrowed psu has been replaced. I dont have any way to test it other than a DVOM and I know that wont work. I have searched around with the numbers off of the transformers and cant find anything, could...Leave a comment:
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Re: Proscan 55LC55S240v69
I did test test the diodes before but didnt think to compare them against the other board, so I will check that tonight. The sm stuff is definately a little harder to check but will try to go over each one comparing it to the good board.
Another question is regarding the caps I already replaced. I see mention of using low esr capacitors. Is there any way to know for sure if the new ones are and would they cause this type of problem? My friend ordered them from Digi-key, some are Panasonic some are Nichicon and he said he ordered the higher...Leave a comment:
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Re: Proscan 55LC55S240v69
I went over everything again that I could remove and test and havent found a thing. My best guess at this point is that it has to do with the load sensing logic part of the ps. Funny thing is that every problem I find on this tv is the exact same ps problem but havent found any one that has figured it out, they just replace the ps board. I almost want to try a new transformer since it looks like they replaced it on the borrowed board but looked around and couldnt find any crosses for it. The challenge of fixing it is driving me crazy.Leave a comment:
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Re: Proscan 55LC55S240v69
Hopefully I will find something and not have to deal with the sm stuff. I really wish I could come up with a schematic for it, as I think that would help narrow it down.Leave a comment:
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Re: Proscan 55LC55S240v69
I knew I was getting some flaky results and ended up pulling some to test. So do I need to pull each individual one to test? What do you do about any surface mount components?Leave a comment:
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