TV Repair - Accidentally brought to life (momentarily) with DMM! - Page 1
Forum section: electronics / repair

author: Joshsstuff
author_rank: Contributor
timestamp: November 24, 2017, 01:43:31 am
content: I was probing voltages on the pins of the TVs Logic board (going to the Time-Control Board) and suddenly it came to life!The power supply did not sound healthy to me, but maybe I'm mistaken.I'm trying to get the video uploaded to listen to the sound it makes.After I power cycled the TV it was was dead once again and I could not reproduce the probing that brought it to life.Specs:Vizio LED TV E70u-D3 (70")Info PDFhttps://support.vizio.com/s/article/E70u-D3-Model-Information?language=en_USOriginal Problem:It was reported to me that the TV became increasingly unstable.It would turn itself off after just a few minutes, and there was distortions on the screen.Finally the TV would display nothing at all.The power cable was replaced, and the TV was power cycled. Both attempts seemed to correct the problem, however now the white power LED will illuminate for a few seconds and go out after a minute, there is no longer any display shown on the screen.Trouble shooting Technique.I intend to check all the power supply capacitors, then move to stand by power, voltage regulators, and voltage levels on other boards.The red label "12.3V" is the pin I was probing when the TV came to life.With the TV plugged in, but in stand by mode, there is 0volts on these pins, however after the power button is pressed 4/7 of them get 12.3 volts.I was checking this when all the sudden the power supply booted up (noisily) and the screen lit up.I was able to feed a signal into the TV, and it displayed it just fine (just a noisy power supply to my ears)The 2nd photo shows my diagnostics of the Power Supply.Pin 13 labeled "PS-ON" has 0 volts in standby mode and 5v when the power button is pressed.The voltage is persistent on this pin, however the "power" led only stays lit for about 5 seconds before fading out. After witch you can again power it on for a brief time.I am not sure if the power supply quality is the underlying issue, or if there is a fault on the main logic board.Can anyone suggest how I can test this?Thanks!

author: tpowell1830
author_rank: Frequent Contributor
timestamp: November 24, 2017, 02:23:08 am
content: Get out your soldering iron and reflow all of those power pins for starters. More troubleshooting if that doesn't work, possibly capacitors or power supply issues.

author: dave_k
author_rank: Frequent Contributor
timestamp: November 24, 2017, 03:59:15 am
content: Agreed. Sounds like your probing flexed the PCB enough to correct an open solder joint...

author: Joshsstuff
author_rank: Contributor
timestamp: November 24, 2017, 04:47:30 am
content: Quote from: dave_k on November 24, 2017, 03:59:15 amQuote from: tpowell1830 on November 24, 2017, 02:23:08 amThat is a valid theory.So here is a closeup shot of the terminal in question, tell me what you think.Here is the top view:I have some concerns about reworking this connector.Does this look bad to you? It seems like a good place to start, but I should mention that once working the TV continued to work until I power-cycled it. And I left it alone while I cycled it. could it be that the DMM connected to ground did something, rather than the probe physically restoring the connection?Another concern is that I may cause a fault. There is a very fine barrier there. (or is that just the solder mask?)If you still think I should solder it I will, but here is the video of the power supply noise:https://youtu.be/WmIciHlb4gQ

author: Joshsstuff
author_rank: Contributor
timestamp: November 24, 2017, 06:43:52 am
content: Anyone know how to interpret the values of this Capacitor?The markings are 1545(M)

author: kripton2035
author_rank: Super Contributor
timestamp: November 24, 2017, 07:19:50 am
content: + pin of C2 , I would reflow ?and of course check capacitors with an esr meter ...

author: Bashstreet
author_rank: Frequent Contributor
timestamp: November 24, 2017, 08:11:42 am
content: What diagnostics have you done to the power unit ?1.Do all power rails work as they should ?2.If not what rails do not work/drop out ?Also that coil whine is not healthy... they seem draw quite a bit of current... hmmCheck what they are drawing.

author: capt bullshot
author_rank: Super Contributor
timestamp: November 24, 2017, 08:55:15 am
content: You should see the capacity / voltage ratings of the capacitors on the other side, facing the PCB. You'll have to lift them from the board.The PS board is a single sided PCB, they are prone to bad solder joints due to thermal stress and old age. The ones you pictured are on a multi-layer board, these usually do not go bad.Look for bad solder joints on the power supply PCB, especially at the pins of larger components (like the caps, transformers, power semiconductors).

author: Armadillo
author_rank: Super Contributor
timestamp: November 24, 2017, 12:43:16 pm
content: Confirm if C12 is 224/50V [0.22uf] capacitor, check its value with a "proper" capacitance meter out of the circuit or simply change it.This capacitor is near to U1 of the power supply board.

author: Joshsstuff
author_rank: Contributor
timestamp: November 24, 2017, 07:12:50 pm
content: Quote from: capt bullshot on November 24, 2017, 08:55:15 amOk, so I found the values. The large Caps are 450v 100uf, small are 25v 1000uf.The most concerning items are the inductors/ transformers, many of them seem bodge soldered from the factory.I will mess with them if it's likely they are a problem, is that the case?Quote from: kripton2035 on November 24, 2017, 07:19:50 amOk, will do.Quote from: Armadillo on November 24, 2017, 12:43:16 pmI'm sorry sir, I do not see C12 (I also looked on the back at the smd caps near u1)Is the Cap you are referring to in the picture?C9 and c11 are both 50v @22uF.Should I check these?Many thanks for the help.Quote from: kripton2035 on November 24, 2017, 07:19:50 am

author: Armadillo
author_rank: Super Contributor
timestamp: November 24, 2017, 07:35:17 pm
content: Quote from: Joshsstuff on November 24, 2017, 07:12:50 pmIs U1 a 8 Pin SO8 package device?. Confirm its a TEA1733. If Yes, then follow the Pin4 connected to a 2K resistor. After the 2K resistor is the C12 in series to it.Edit: Sorry those are 0805 smd devices. Search on the copper side. Use a magnifying glassEdit: You took photo on the component side, why no photo on the copper side?Edit: At the same time, also check the capacitor connector to pin 6 to ground, measure ohms across it, just make sure it not shorted example high ohms [turn off power to measure it].

author: capt bullshot
author_rank: Super Contributor
timestamp: November 24, 2017, 07:46:41 pm
content: In general, with single sided PCBs, the THT solder joints of thermally or mechanically stressed components are prone to go bad over time. That might be the transformers, also the connectors and the heat sink mounted semiconductors.With some experience you may be able to see the wear, it's like a ring around the pin where the solder is cracked. At some point, the pin totally looses electrical contact. Anyway, just re-soldering pins usually doesn't harm.If a component gets really hot while in service, the solder joints also can go bad, on some boards you can see the discolouration of the PCB material, this is a hint to check the solder joints.Electrolytic capacitors can dry out, often there's a small one on the primary side of the supply unit that is required to properly start the SMPS, from your description I would guess that's not the issue here, anyway, did you check all outputs of the supply?

author: Joshsstuff
author_rank: Contributor
timestamp: November 24, 2017, 09:05:06 pm
content: I won't have access to a proper ESR meter for a few days. In the mean time this is the best I have:The reading fluctuates between 0.016 Ohms and .31 when I first took it out (maybe too hot?)Quote from: Armadillo on November 24, 2017, 07:35:17 pmOk, sorry sir, from the values you asked about I assumed it must be an electrolytic on the front side.How about his picture:Quote from: capt bullshot on November 24, 2017, 07:46:41 pmYes sir, the voltages are recorded in my original post.Unfortunately there is a very brief window to measure voltages before the TV shuts itself off.(So I can't test if the voltages are stable while on, however the 16V is stable)Was there a specific reading you think would be important?

author: Armadillo
author_rank: Super Contributor
timestamp: November 24, 2017, 09:24:49 pm
content: Yeap , cant see clearly, but you need to trace it and find the 2 capacitors. Its all 0805 mlcc caps.take a close up when you find it.For the 0.22 uF cap, you will need to take it out to measure its capacitance or simply replace it.Just don't under-estimate small capacitors.Edit: Just don't spend too much time on big caps. The area I asked you to search is the nerve center of everything.Edit: From your photo It looks like Pin 4 is connected to R7 and then R7 is connected to C5. If so, this is the 0.22uf I was talking about. And Pin 6 is connected to C4. Can't see very clearly. Trace the Pins. Labelling may not be the same as your board.

author: capt bullshot
author_rank: Super Contributor
timestamp: November 25, 2017, 10:13:11 am
content: OK, so the output (16V) of the PS gets active for a short time while the PS-ON voltage stays at 5V? Does the LED output the same?To me this looks still like a fault on the PS board, located in the main SMPS. The 5V appears to come from another auxiliary SMPS, while the main SMPS gets enabled and disabled by the PS-ON control signal.

author: NeedsMoreFlux
author_rank: Newbie
timestamp: November 26, 2017, 03:06:33 am
content: I skimmed through.Have you been checking for shorts to ground?I have a TV that is supposed to be putting out 24 volts to the backlight inverter.I replaced the burned fuse on the inverter board.It outputs 24v when unplugged. But when plugged into inverter it outputs 0v(good think it has short detection safety built into the power supply board).I thought it was 1 of the 4 caps that was shorted.After removing all 4 it was still shorted to the positive leg of the cap I suspected.Turned out to be 1 or 2 of the 14 mosfets shorted to ground.I'll be ordering them off Digi-Key for $0.50 a piece.

author: NeedsMoreFlux
author_rank: Newbie
timestamp: November 26, 2017, 03:09:10 am
content: Oh, and what was the area you were poking around in when it decided to work?If you can light up a diode by testiing with a multimeter then I assume the injection of like 1v @ 15ma(I don't know the real number) made a chip wake up. or it completed a circuit.

author: Joshsstuff
author_rank: Contributor
timestamp: November 26, 2017, 04:34:29 am
content: Quote from: capt bullshot on November 25, 2017, 10:13:11 amThe 16v comes on as soon as the mains are connected.There is 5V only for the brief time after the power button is pressedI'm sure there is a way to trick the P. Supply into booting up, (like the PC P.Supply paper clip trick) but I'm not sure how to do it here.Quote from: NeedsMoreFlux on November 26, 2017, 03:06:33 amGood idea about checking the shorts, I should have thought of that earlier.I just checked though, and nothing goes to the chassis ground, I double checked.I was hoping to not need any mosfets, I'm not a fan of the heat sync design to get them out.Quote from: NeedsMoreFlux on November 26, 2017, 03:09:10 amIt was one of the pins labeled "12.4V" in the original post (on the main logic board)Quote from: Armadillo on November 24, 2017, 09:24:49 pmI'm attaching a composite of the entire board:most of those passives by u1 are epoxyed to the board, but if your pretty sure they could be causing the 'missing cylinder' sound, I can rip them out and test them.There is no "C12" that I can find.Can you tell me please, do you have this board that you are looking at? Or are you consulting a schematic?Where do you see the "C12"?Thanks folks,I'm going to put the Cap back and re-test the rail voltages.Let me know if you come up with any tests to run while I'm at it.

author: capt bullshot
author_rank: Super Contributor
timestamp: November 26, 2017, 08:59:02 am
content: For now, thinking about your results and the botton side photo of the PS board, I'd move my guess away from the PS to the main logic board. Reason: there's only one output voltage per transformer (16V and LED), and the 16V appear to work. Moving to the logic board also agrees with your first observation touching the 12V output there.So my guess is now: There's something with the logic board. Did you try pushing other components, and comes it alive then?I remember having seen a heatsink on the logic board, probably there's the big main chip underneath. Remove the heatsink and check the pins (if it isn't a BGA). In case it's a BGA, these sometimes fail on random balls, people reported fixing this by heating the whole board or reflowing the chip.

author: martinator
author_rank: Contributor
timestamp: November 26, 2017, 10:34:48 am
content: It's very difficult to see what's going on from your photos. Do you have a magnifying glass or something?If you have a magnifying glass you can sometimes take photos through the magnifying glass.Natural light will help you see flaws more easily than artificial lighting.From one of the photos it looks like one of the joints for D3 on the rear of the board is bad, but this could just be glare from the camera.I would start by re-soldering all of the jumper wires and checking with the multimeter that both pads are connected across the jumper. As you go along soldering the jumper wires examine each area visually in a careful and controlled manner. If it still doesn't work do the diodes. I think this is most likely a mechanical issue and not a faulty component one.