changed fuse, blew up power supply - Page 1
Forum section: electronics / repair

author: kgavionics
author_rank: Regular Contributor
timestamp: May 03, 2017, 09:40:59 pm
content: HiMy friend gave me a non working samsung plasma tv model pn43d450a2d , i took it apart and found that the fuse was open, so i changed it with the same power rating (250V 8AH).The second i plugged the tv to the power i saw a smoke coming out from 2 power Mosfets.I'm wondering what i have done wrong.Normally, if something goes wrong, the fuse would do it's job right!!Can someone explain to me what's going on???thanks in advance

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: May 03, 2017, 10:11:35 pm
content: You should look for the reason why a fuse blows before replacing it. Clearly there is a short somewhere and now you've possibly made the situation worse. Check the bridge and go from there.

author: Geekfix1706
author_rank: Newbie
timestamp: May 03, 2017, 11:08:13 pm
content: That fuse did do its job, it ruptured under a fault condition, saving other components from damage. If you replaced it with an 8A fuse (I don't recall seeing an 8A fuse in any plasma TV) then you have likely done more damage. The power supply could have failed due to a fault elsewhere in the TV in this set the Ysus panels are renowned for failing. Sorry to sound harsh but if thinking replacing a blown fuse will magically fix the at TV esp a plamsa then you need to read no learn a bit more. Try putting the model number of the set followed by "dead" into google, chance is others have had the same problem and might be be able to help.

author: Raff
author_rank: Regular Contributor
timestamp: May 03, 2017, 11:23:40 pm
content: It might be an idea to make yourself a "dim bulb tester" to temporarily replace the fuse when testing, those slow blow fuses can be expensive.Raff.

author: Samogon
author_rank: Frequent Contributor
timestamp: May 03, 2017, 11:26:02 pm
content: 8A did its job by allowing to blow almost all Y-board, there is 1A fuse if I remember. There is hybrid which usually gets shorted by overheating, and 1A fuse does its job protecting other components. Now i think you have MOSFETS blown also optocoupler and God knows whst else. I personslly seen exactly same scenario.If you get lucky you can order hybrid or even Y-board. At the time i decided just to throw this TV heater away.

author: Samogon
author_rank: Frequent Contributor
timestamp: May 03, 2017, 11:53:26 pm
content: Here is good group of people sharing their TV repair experiencehttp://www.badcaps.net/forum/forumdisplay.php?f=31They can help a lot.

author: kgavionics
author_rank: Regular Contributor
timestamp: May 04, 2017, 12:08:27 am
content: Thanks guys your replysIt turned out that the fuse was 250V 10AH not 8AH .after i blew up the power supply, the fuse still working.This time i admit i'm dumb.I learned the lesson.

author: naldo
author_rank: Contributor
timestamp: May 04, 2017, 01:14:45 am
content: Good night to all here! This fuzible is likely to be 5A, the higher (capacity) the higher the damage will be, it was scaled in the design of the board for such a value. If it did not have the fuzible for sure several components would exprodir, could even catch fire!...

author: kgavionics
author_rank: Regular Contributor
timestamp: May 04, 2017, 01:58:06 am
content: Another thing i want to point out.Why the service manual says to only change the fuse.That's why i didn't bother myself to check if there is a short in the power supply.

author: naldo
author_rank: Contributor
timestamp: May 04, 2017, 02:14:58 am
content: It is to REPLACE for 1 other of the same value!

author: P90
author_rank: Frequent Contributor
timestamp: May 04, 2017, 10:05:18 am
content: apparently, common sense isn't all that common...

author: Rasz
author_rank: Super Contributor
timestamp: May 04, 2017, 10:44:46 am
content: there is a reason its called service manual and not user manual, different expectations

author: Seekonk
author_rank: Super Contributor
timestamp: May 04, 2017, 11:07:26 am
content: Your friend is pretty smart. Now you have to dispose of the E waste.

author: P90
author_rank: Frequent Contributor
timestamp: May 04, 2017, 11:18:52 am
content: Quote from: Seekonk on May 04, 2017, 11:07:26 am

author: wraper
author_rank: Unknown
timestamp: May 04, 2017, 11:30:34 am
content: Quote from: kgavionics on May 03, 2017, 09:40:59 pmReplacing fuse without checking everything else, this is what's wrong. Fuse in SMPS very rarely blows up without something else being faulty in the first place.

author: Nusa
author_rank: Super Contributor
timestamp: May 04, 2017, 12:23:32 pm
content: If the label on the original fuse was FM801S, that is a 3.15 Amp 250V fuse.

author: macboy
author_rank: Super Contributor
timestamp: May 04, 2017, 01:13:39 pm
content: Quote from: P90 on May 04, 2017, 11:18:52 amTrue, but there are places that will pay you $ by the pound for it!I was going to suggest there was no way the original fuse was 8 A, I mean that's nearly 1kW at 120 V. But then I realized it's a plasma TV, so very plausible. No wonder people stopped buying those things.I also wanted to point out that "dim bulb testers" suggested by others don't work on circuits designed to draw 8 A. If he had disconnected the power supply from the load/TV, then it might (but would the power supply be designed to start without it's normal load? who knows). They work great for things like audio amps, where you think there might be shorted output transistors. An audio amp will draw very little power after the initial surge, if you don't have speakers/load connected. They also work for SMPS with a minimum load on it, but not with a plasma TV trying to load it.

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: May 04, 2017, 01:23:38 pm
content: Quote from: macboy on May 04, 2017, 01:13:39 pmPeople moved to LCD because they were cheap. The same people didn't care for the better picture quality of plasma TVs and Panasonic stopped production of TV-phile products like the VT60.Ultimately the market wanted grey blacks, backlight bleed, gamma shift, shit contrast instead, while plasma was only rivalled by CRT. OLED is close but LG panels still suffer from terrible QC issues.

author: P90
author_rank: Frequent Contributor
timestamp: May 04, 2017, 01:30:06 pm
content: 42" plasma tv consumes 300-400 watts, so a 3A fuse or there about sounds right...