Dell LCD TV turns off by itself after a few seconds - Page 1
Forum section: electronics / beginners

author: kasumyku
author_rank: Regular Contributor
timestamp: April 21, 2019, 05:50:15 pm
content: Hi everyone,I just got a Dell Tv W3207C. It powers up, backlight comes on for a couple of seconds then it shuts of by itself. Only once I had it on for a bit longer and I could see onscreen menu for a brief moment then it disappeared and it shut off again.Things that I tried and found so far:-looked for obvious burn marks, swollen caps: seem to look OK-checked power board output voltage:not OK. 3 pins should read 5Vdc but instead they read 1.591Vdc as bellowPower board has 3 output connectors:1st connector: +12VS reading 11.8VdcGND 0Vdc+5V 1.591Vdc+5V2-STBY 5Vdc+3V 3Vdc2nd connector: +24V 24.32 VdcGND 0VdcON/OFF 0.466Vdc3rd connector: GND 0Vdc+24V 24.04VdcI removed T-con and inverter connectors one at a time to see if there is any difference in the output voltage but nothing changed.I'm not sure if I really narrowed it down correctly to the power board or there's more to it. I also searched online for service manual and no luck.Any advice would be really appreciated because I don't really know where to go from here due to my little knowledge of troubleshooting electronics to component level.Thank you in advance!!

author: thinkfat
author_rank: Unknown
timestamp: April 21, 2019, 08:09:49 pm
content: Check all power rails for ground shorts. Might be a cracked filter cap. Check for heat sources, freeze spray can be helpful.Gesendet von meinem Nokia 6.1 mit Tapatalk

author: dzseki
author_rank: Frequent Contributor
timestamp: April 21, 2019, 08:20:12 pm
content: I had a similar problem with a DELL mointor before, there, some of the CCFL tube connectors were "burnt". As there were some sort of preformed conductive rubber thingies those were holding the CCFL tubes in place and making the electrical contact too to the inverter. Some of them got corroded and failed to make proper contact and it was shutting down eventually. This monitor used an LG panel I think.I managed to repair this with soldering all the CCFL tubes with a thin wire to the inverter contact, while I left the rubber stuff there for the mechanical support.

author: Brumby
author_rank: Unknown
timestamp: April 22, 2019, 01:33:39 am
content: This may not be relevant, but it is a curiosity question:Is this 1.591Vdc always around the same value - or does it change? If it does change, what is the timing?If you have disconnected all off-board connections and the voltage is still low, then the likelihood there is a problem on the power board is going to be high. Can you get a good close-up photos of this board - top and bottom would be good. (Remember - good framing, good lighting and good focus make such photos more useful.)

author: MosherIV
author_rank: Super Contributor
timestamp: April 22, 2019, 05:32:04 pm
content: HiGood work so far.QuoteCapacitors can fail without outward signs.My bet is on capacitors on the 5V rail gone bad.Try soldering new cap across this rail and see if the monitor starts working.

author: thinkfat
author_rank: Unknown
timestamp: April 22, 2019, 05:43:48 pm
content: Quote from: MosherIV on April 22, 2019, 05:32:04 pmThat do not make sense, it is likely a leaky capacitor or a short. Soldering good caps over bad ones will not make it work.Gesendet von meinem Nokia 6.1 mit Tapatalk

author: kasumyku
author_rank: Regular Contributor
timestamp: April 23, 2019, 12:38:35 am
content: Thank you all for the responses!!Quote from: Brumby on April 22, 2019, 01:33:39 am1.591Vdc is constant, doesn't change.I have attached a couple of photos of both front and back of the power board.Please let me know if you need more up close pictures of a particular area/ component.Quote from: thinkfat on April 21, 2019, 08:09:49 pmI really appreciate the advice but I'm still a newbie and need to mention that I only have basic knowledge about electronics and I'm learning things everyday from people like you, so please bear with me.I'm not entirely sure how to check for ground shorts. I'm assuming that I need to disconnect the power, set multi-meter to resistance then attach one lead to ground and the other to each of the output pins that I mentioned earlier and look for very low resistance, something like 0.1 to 0.3 ohms??Quote from: dzseki on April 21, 2019, 08:20:12 pmThat will be my next step if the power board doesn't do the trick.Quote from: MosherIV on April 22, 2019, 05:32:04 pmThanks for the encouragement!I think I found the cap that's related to the 5V rail (please see picture attached). It looks like its a 10V 1000uF , the positive lead of the cap is connected to the 3 pins of the 5V output.I removed it from the circuit and its reading 887uF.

author: Brumby
author_rank: Unknown
timestamp: April 23, 2019, 01:30:00 am
content: Good job on the photos.Unfortunately, nothing seems to jump out at me - but I've not had a lot of experience with TV switchmode power supplies.Photos are always good to have, though.

author: davep238
author_rank: Contributor
timestamp: April 23, 2019, 09:02:15 pm
content: If you just got it, can't you return it rather than trying to fix it?

author: mariush
author_rank: Super Contributor
timestamp: April 23, 2019, 09:18:44 pm
content: It could be that the 5v output of the power supply is good, but something at the other end of the cable is shorted or with problems, causing too high power consumption from 5vThink of it like the power supply entering current limit mode and limiting the output voltage to 1.59vYou could try disconnecting the 5v wire(s) from the connector and placing a multimeter in current mode between the connector and the wires to see if the current is excessive or not.If you have a decent clampmeter that can measure current in DC mode, then simply isolating the 5v wires and inserting them through the clamp of the meter could be enough for a quick test.

author: MrAl
author_rank: Super Contributor
timestamp: April 23, 2019, 10:22:42 pm
content: Quote from: kasumyku on April 21, 2019, 05:50:15 pmHi,That's what happens when the electrolytic caps go bad. You said you visually inspected them but maybe you have to do some electrical tests. I've had same thing happen on an AOC tv set and other things too.