Proscan 55LC55S240v69

[awyatt2]

Re: Proscan 55LC55S240v69

it is a switching power supply, it dosent turn on until it is loaded. you cant check esr in circuit if there are more than one cap if they are in series then your meter gets fooled. i own three esr testers the blue, the peak and the mul333, none will read right in circuit unless there is just one. check the diodes and any associated fets.

[gsmy]

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?

[awyatt2]

Re: Proscan 55LC55S240v69

you need to lift oe leg at least on smd's better off hoping they are ok. if you are reasonably carefull and have a steady hand tweezers and a solder wick for removal. i use a fair amount of 60/40 to help remove them just put a fair amount to it before you use the solder wick, then after you get as much solder as you can off with the wick pick it up while still applying heat with iron

[gsmy]

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.

[gsmy]

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.

[selldoor]

Re: Proscan 55LC55S240v69

I know awyatt2 keeps asking but cant see a reply - have you tested the diodes.
It usual to have to remove but as you have two boards just test resistances each way
on each diode and see how it compares with the other board.

[gsmy]

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 temperature rating (105) so they would be better and last longer.

[selldoor]

Re: Proscan 55LC55S240v69

Panasonic and Nichicon are respectable brands and 105deg often have lower esr than 85deg. You can tell for certain by the series Panasonic FM and FR are good FC less so.

[gsmy]

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 this be a specific part not available?

[vinceroger69]

Re: Proscan 55LC55S240v69

its a risk but can you just swop the transformer over to test it on your board?

[gsmy]

Re: Proscan 55LC55S240v69

I considered it but dont want to take the chance and have 2 bad power supplies.

[selldoor]

Re: Proscan 55LC55S240v69

How about trying the faulty power supply in the set that the borrowed supply is out of.
May have missed it but cant spot that you tried that.



Edit Just to be sure which transformer is buzzing - board number?

[gsmy]

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.

[selldoor]

Re: Proscan 55LC55S240v69

Yes I understand all that What is the board number of the transformer Txx???

I was not suggesting a transformer transplant as per vinceroger69 I am suggesting
trying the whole power board in the other set. - or does the other set not work?

[gsmy]

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?

[vinceroger69]

Re: Proscan 55LC55S240v69

this is of another forum that uses the t801 dont know if the info is helpfull though?

T801 is the PSU transformer, again these either work or they do not, they can cause noise if the core is loose or cracked but not broken.

The main reason for noise from the psu transformer is due to a low frequency signal superimposed on the normal switching signal.

This again will be caused by a failed capacitor some where in its feed back circuit or the supply to the regulator IC.

ebay do a repair kit for these there seems a lot of capacitors (18) i wonder if one of these kits would solve your issues?
http://www.ebay.co.uk/itm/Repair-Kit...item4cfbc7820d

[selldoor]

Re: Proscan 55LC55S240v69

As I see it you have nothing to lose by trying it.
You have cross checked voltages and components with the board which works yet it still doesnt work. It would just verify that it really doesnt work.

Anyway to move on -I have attached a pic. -(could do with a clearer picture of this side of the board )
As you do not want to transplant the transformer I suggest you resolder all the connections - some of them look a bit grey so may be failing I have marked them in the picture.
There is also what I think is a wire link to resolder and what looks like a single joint in the smallest red loop.
Please can you also do a close up of the yellow box area.


@vr69 He has already replaced all the caps on the power supply - post#5

[gsmy]

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.

[gsmy]

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.

[vinceroger69]

Re: Proscan 55LC55S240v69

cheers selldoor missed that bit.