T.v. psu - Page 1
Forum section: electronics / general

author: snipersquad100
author_rank: Frequent Contributor
timestamp: December 06, 2013, 07:53:32 pm
content: HelloI got a Samsung LE40R88 which wont turn on. The psu bn4400165a. I only have the psu and main board as it was posted to me for repair but they didn't send the cable to connected them. So I shorted "ps on" pin 1 with pin 3 5v to switch on the power supply, I don't know if this is addviseable but it did switch on the other voltages. Im only reading 11v on the 12v & 13v rails. I checked the caps with an esr meter I think they were ok as they were on average 0.5ohms higherthan recommended. I have a schematicthanks

author: tom66
author_rank: Super Contributor
timestamp: December 06, 2013, 09:55:02 pm
content: 0.5 ohms is too high for caps like that, probably much higher when pulled!You also need to provide sufficient load to some types of PSU for them to work properly - for example a brake light on the 13V line can work well and provides about 20 watts load, sufficient to keep the PSU in regulation.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: December 06, 2013, 10:01:45 pm
content: will try that.am I ok to short ps on to 5.2v to start up the unit?

author: tom66
author_rank: Super Contributor
timestamp: December 06, 2013, 11:24:29 pm
content: I would always put a 100 ohm resistor in series to limit fault current, also I think these Samsung PSUs work with an active LOW signal (the PS ON must go low to turn PSU on.)

author: snipersquad100
author_rank: Frequent Contributor
timestamp: December 07, 2013, 12:51:33 pm
content: Ive put a 12v brake bulb across 13v rail and ground and the voltage on the 12 and 13v rails has droped to 3.8 volts.

author: Monkeh
author_rank: Super Contributor
timestamp: December 07, 2013, 01:34:30 pm
content: Change the caps already.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: December 07, 2013, 03:58:12 pm
content: The ESR on the caps are within tolerance.

author: Monkeh
author_rank: Super Contributor
timestamp: December 07, 2013, 03:59:53 pm
content: Quote from: snipersquad100 on December 07, 2013, 03:58:12 pmYou gave a figure of 0.5R. That is not within tolerance, that is so far out of tolerance you may as well be using a wet toothpick for a capacitor.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: December 07, 2013, 04:34:02 pm
content: Sorry I ment 0.05. Where for instance the 1000uf/25v should be no more than 0.1 ohm, Its reading 0.15 ohm. Even the new ones are reading the same.

author: tom66
author_rank: Super Contributor
timestamp: December 07, 2013, 05:44:08 pm
content: Just to be sure try using 5W element on brake light?BTW, do not try using headlamp... They are 65W and draw too much current.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: December 08, 2013, 12:44:52 pm
content: ive put a 5w bulb in and the voltage has gone from 3.8 to 7v.Without the load the 12v rail is 12v and 13v rail is 12.15v is that normal?

author: snipersquad100
author_rank: Frequent Contributor
timestamp: December 08, 2013, 01:25:53 pm
content: Just took some voltages with and with out a load on the schematic.Black writing is no load red is with load.

author: Unknown
author_rank: Unknown
timestamp: December 08, 2013, 01:50:12 pm
content: Just had to replace 4 x 1000uF smoothing caps on the output of the switching PSU board in our Samsung 32" LCD TVThe fault that altered us to their being a problem was a constant low level buzzing sound (level didn't alter with TV volume setting). Really annoying it was.It's a common fault with Samsung TV's it seems, they use cheap electrolytic caps. The ones I took out measured about 215uF (should be 1000uF) and had bulging tops (a sign they are now useless). Don't have an ESR meter so couldn't tell you what the ESR was.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: December 08, 2013, 02:03:51 pm
content: I bet the esr was right high, the caps here seem to be ok, I also read they use cheep caps so I will replace them with higher voltage higher temp ones, I don't think it fix my problem but might save a problem in the future.