Samsung NPT4254 PSU and my dumb ass.

[Chaiyz]

Please excuse me for being a dumbass. A friend brought me a Samsung NPT4254 I'm used to seeing these and I quickly saw that a couple of caps were bulging and one of the fets had a cold solder. Once I checked the caps, I just had 4 bad (high esr on my meter). These were CB855, CB857, CB819 and CB816.

I grabbed some new 1000uf 25V's replaced the caps and fixed the intermittent fet connection. I plugged the board back in and nothing. Not only does it not power cycle, it does nothing. I pulled the board again and after looking a second time I relize that 2 of the caps I removed should have been 470uf 35V but now I don't know which ones.
I mistakenly replaced all 4 with 1000 x 25v and need to know which ones were supposed to be 470uf 35v. Anyone know?

Anyone know of a sheet or somewyhere I can find this?

Chaiyz

[tw2005]

Re: Samsung NPT4254 PSU and my dumb ass.

CB855, CB857
470uF,35V

Had trouble finding CB819 and CB816

Found CX819, CX816
1000uF,25V

Was the model meant to be HPT4254 with a BN44-00161A or 162A PSU?

https://www.badcaps.net/forum/showth...ht=bn44-00161a

https://www.badcaps.net/forum/showth...-00162a&page=3

[Chaiyz]

Re: Samsung NPT4254 PSU and my dumb ass.

Thank you so very much. Yes it's the HPT4254 with the 161/162 PSU.

I'm usually very studious when removing caps. Unfortunately, I pulled 2 and saw they were 1000uf 25v and just replaced all 4 with 1000uf 25v's.

You should have seen the look on my face when I looked through the caps and realized I'd missed the two 470uf 35v's.

Anyway, I'm going to desolder put in the right caps and hope this thing fires.

[Chaiyz]

Re: Samsung NPT4254 PSU and my dumb ass.

Just replaced CB855 and CB857 with correct 470uf 35v and nothing.

Today before I opened it up, you could plug it in and hear it cycling. I checked ESR on all caps and replaced those that were bad. I had a single bad solder joint on one of the fets that connect the heatsync rail and I did clean the terminal with kester and when I resoldered it all looked good.

Now I get less than nothing. Time to start from scratch I guess.

[tw2005]

Re: Samsung NPT4254 PSU and my dumb ass.

If it's just continuously clicking on/off, check Fuse F802 could be open, VS or VA ccts could be blown.

So check long heatsink in the middle for shorted FETs. Pay particular attention to the SMD 3 pin diodes under the board locations as below.

I'm playing with the 50" model which has the same PSU but with upgraded FETs there but I have blown fuse, both FETs shorted for the VS line because of a failed upper buffer, shorted out Ymain and then blew the Vs line.

So far the VA FETs seem ok but some of those diodes are shorted there as well as the VS section. if you miss these chances are the VA line will blow when you power it up after repair.

VS
QS801,QS802
DS801,802
.( RS867, RS869), (RS862 and RS878).
RS863 and RS868

VA
DX803,DX804
RX802, RX803, RX832, RX833
QX801 and QX802

RX804 and RX805