Hitachi TV will not turn on and no stand by LED - Page 1
Forum section: electronics / repair

author: pieshower
author_rank: Regular Contributor
timestamp: April 18, 2020, 09:32:08 pm
content: So I am fairly new to electronics been trying to read as much as I can for I want this to be my career.My friend gave me a Hitachi LE65k6r9 that would not turn on. The stand by light does not come on either. I've checked the stand by voltage on the power board after disconnecting the wires that lead to the main board. The voltage reads 5v as it says printed on the pcb.However, when plugging the wires back in and checking all the pins i get voltages less than what should be there and they fluctuate. There is also a faint but obvious popping noise. Im not sure what the problem is, any ideas?

author: Manul
author_rank: Super Contributor
timestamp: April 18, 2020, 09:55:45 pm
content: The popping noise probably means that power supply overcurrent protection kicks in. So it shuts down and restarts in a cycle. There may be a short circuit.When power supply board is disconnected from main board, you get stable 5V and other voltages are zero, yes?When plugged to main board, 5V fluctuate? Are there any other voltages apearing (which was before zero)?

author: pieshower
author_rank: Regular Contributor
timestamp: April 18, 2020, 10:18:53 pm
content: Yes, when I disconnect the power board from the main board and probe the stand by pin I get a stable 5v but the other pins all read 0v.When I plug the main board back back in the stand by pin drops to around 3.2v and fluctuates between 3v to 4v. Theres another 5v pin that drops to 2v and fluctuates between 2v and 3v. There is also two 12v pins the fluctuate between 9v and 11vIm not sure if its supposed to drop that low but its definitely not a stable voltage.Edit* Also I would like to mention when I disconnect the power board from the main board and apply power there is still a popping noise though it becomes a irregular beat.

author: Manul
author_rank: Super Contributor
timestamp: April 18, 2020, 10:36:02 pm
content: Yes, of course, normaly voltages should be stable. The question is, is it the main board or power supply problem. Not sure.For example you can try to measure power rails on the main board with a diode test mode. Disconnect power supply. Set multimeter to diode test mode. Connect negative lead to main board ground and positive lead to the points where standby 5V, 5V, 12V are supposed to come. Note what does multimeter show after the reading stabilises.

author: floobydust
author_rank: Super Contributor
timestamp: April 18, 2020, 11:25:27 pm
content: Hitachi 65" LE65K6R9 50326502000060 power supply board uses cheap crappy CapXon capacitors, which I would test and replace.

author: pieshower
author_rank: Regular Contributor
timestamp: April 19, 2020, 12:33:06 am
content: Stand by pin read 1102. One of the two 5v pins read 794 and the 12v reads 1518 then goes to OL.Also it could very well be the capacitors. When I was searching I read something about failed capacitors could cause voltage/current irregularities that can trigger the over current protection.

author: Manul
author_rank: Super Contributor
timestamp: April 19, 2020, 12:50:24 am
content: That measurments seems adequate. Next I suggest to try to turn on the power supply alone without the main board. There should be a pin on a power supply, which controls turn on (full turn on with all voltages). I don't know how it is named on your board. Usually you give 5 volts to that pin (taken from 5 volts standby) and the power supply should start fully. Observe if it does start and how are voltages.

author: pieshower
author_rank: Regular Contributor
timestamp: April 19, 2020, 01:05:13 am
content: There is one pin labeled STB when I connect it to 5v the popping noise starts and the values go from 87 then climbs to 210 and jumps back down. The two 12v both read 1050 and jumps around like +-10. The 5v's read 1500 and then goes OL.

author: Manul
author_rank: Super Contributor
timestamp: April 19, 2020, 01:24:08 am
content: Wait, something is wrong. Can you list pins, or even better take a picture what is written on the board. Also you should go on voltage measurement on the multimeter.

author: pieshower
author_rank: Regular Contributor
timestamp: April 19, 2020, 01:33:21 am
content: Ah I was still on diode tester mode. All the pins read 5v.

author: Manul
author_rank: Super Contributor
timestamp: April 19, 2020, 01:49:33 am
content: So you connected 5VSB which is 5V standby to STB? What you mean by saying all pins read 5V? Can you check again voltages on +5 and +12. What are these voltages, are they fluctuating?

author: pieshower
author_rank: Regular Contributor
timestamp: April 19, 2020, 01:59:23 am
content: well Im connecting the negative lead to 5VSB and then touching the various other pins with the positive lead which all read -5.2 to be exact no fluctuations.

author: Manul
author_rank: Super Contributor
timestamp: April 19, 2020, 02:15:51 am
content: Normaly all voltage measurements are done with reference to the ground (GND). So negative lead should be connected to ground.If we convert to ground reference it seems that you measured zero on every pin. It is puzzling why it does not start. It is starting when connected to main board (I mean at least something appears on +5 and +12). That needs some investingation. I'm off for today. Good luck and take care, these power supplies are dangerous.

author: Manul
author_rank: Super Contributor
timestamp: April 19, 2020, 12:50:55 pm
content: My guess is that you did not keep STB connected to 5VSB while measuring. If you are planing to troubleshoot the power supply you should get some jumper to short these pins. A standard jumper (used on PC moterboards and so on) may fit.

author: pieshower
author_rank: Regular Contributor
timestamp: April 19, 2020, 03:18:10 pm
content: Yes I was thinking it was because the cable was connecting the two pins. I will do that now.

author: aqibi2000
author_rank: Regular Contributor
timestamp: April 19, 2020, 03:28:49 pm
content: If this is a LED tv then disconnect the backlight.

author: pieshower
author_rank: Regular Contributor
timestamp: April 19, 2020, 03:35:04 pm
content: Ok after jumping the 5VSB to the STB pin the two +5v pins jump between 4.5 and 4.89 and the two +12v pins jump between 10.5 and 11.8. It just fluctuates between those values.

author: Manul
author_rank: Super Contributor
timestamp: April 19, 2020, 04:48:37 pm
content: Is this with backlight disconnected? No loads on power supply? Then it seems it is bad. Could be electrolytics, but not 100%.

author: pieshower
author_rank: Regular Contributor
timestamp: April 19, 2020, 05:10:53 pm
content: Yes I unplugged the back lights and the values did not really change much.Im going to spend the next few hours checking these CapXon caps. Seeing that they are already known to go bad.

author: pieshower
author_rank: Regular Contributor
timestamp: April 19, 2020, 05:36:26 pm
content: Ok so I've already stated I'm fairly new to this stuff so forgive me if this is a silly question, but I can't find anything on the web. I removed one of the caps and it reads within the capacitance range but when I measure the resistance its like 6 Mohms. Is that fine?I unfortunately do not own a ESR meter.

author: Manul
author_rank: Super Contributor
timestamp: April 19, 2020, 05:41:04 pm
content: It is fine, but it does not give information about ESR which is the most important. For that you need ESR meter, or some DIY ESR tester.

author: pieshower
author_rank: Regular Contributor
timestamp: April 19, 2020, 05:44:18 pm
content: I do have a signal generator and a oscilloscope.

author: Manul
author_rank: Super Contributor
timestamp: April 19, 2020, 05:49:01 pm
content: 100 kHz is usually a standard if you want to compare to the datasheet values.

author: pieshower
author_rank: Regular Contributor
timestamp: April 19, 2020, 07:43:39 pm
content: My problem is I don't have one of those splitters. So I'm taking a two lead from the generator putting the negative and positive to the negative and positive of the cap and probing the positive with a oscilloscope. I also have the ground lead to the negative. Not sure if this will work but this is what I get.I think I just need to get a ESR meter. Gonna have to eventually anyways haha.Also its annoying the pictures are going sideways

author: Manul
author_rank: Super Contributor
timestamp: April 19, 2020, 07:49:01 pm
content: You must add some resistor, don't connect signal generator output directly to the capacitor. It is almost shorting your signal generator.

author: Manul
author_rank: Super Contributor
timestamp: April 19, 2020, 07:51:44 pm
content: Resistor and capacitor then works as a voltage divider, so you can actually calculate ESR, as show in the video.

author: pieshower
author_rank: Regular Contributor
timestamp: April 19, 2020, 09:57:00 pm
content: Well I tried to do it as others have shown in several videos and I'm still getting wonky unstable readings on the oscilloscope. I also tried to calculate it based off of what I got and it was around 1 ohms, not really sure if this is accurate. Seeing I don't think I did the wiring right.I'm going to take a break. I order a ESM seeing I'm going to need one anyways. Thank you dearly for the help. I will return if I need any more help that I couldn't find searching the internet or my books I have.Hopefully I can get this fixed and have a nice new 65 inch TV.One last thing, I find it difficult to just put this down haha, I noticed one of the capacitors has a small indention on the side of its chassis. Could be bad? Its also a CapXon.

author: Manul
author_rank: Super Contributor
timestamp: April 19, 2020, 10:47:34 pm
content: Small indention normally do not cause problems. You can just replace them all anyway. Even if the problem is something else it will be good for the future.

author: Manul
author_rank: Super Contributor
timestamp: April 19, 2020, 10:54:41 pm
content: Also it whould be interesting to look at the output voltage with a scope, on the moment when power supply is switched on, how it rises up and what happens. But be careful with a scope ground. There was a video by Dave called something like "how not to blow your oscilloscope". Recomended to watch.

author: pieshower
author_rank: Regular Contributor
timestamp: April 20, 2020, 02:40:44 pm
content: Alright I'll give that a go.

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 12:04:59 am
content: So I used my ESR meter to test the caps in circuit and they all appear to be fine. I'm going to note what happens when you turn it on with the oscilloscope.

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 01:03:38 am
content: Ok so after looking at it through the oscilloscope Im getting a shark tooth wave form for both 5v and 12v outputs. The +12v rises to a peak around 13v then falls to 8v with a period of 384ms. The +5v rises to a peak around 5.52v and falls to 4.24v with a period of 396s.

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 01:19:02 am
content: Seems like it can not regulate (lost feedback or something), because it is overshooting quite heavily. Does a voltage waveform look clean, thin and without ripple? Nice sharp sawtooth?

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 01:58:48 am
content: Yes very uniform and sharp.

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 02:11:01 am
content: In my opinion there should be a problem with feedback. It can not sense output voltage correctly, overshoots and OVP (over voltage protection) kicks in. Good place to start is to trace which one of optocouplers is for feedback. Optocouplers are these 4 pin packages near transformer. My guess one is for feedback, one for OVP and one for power on signal.

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 03:02:56 am
content: Ive diode test the one side and read as such: 1 reads about a 1.8v drop, 1 reads 2.7v drop, and the last reads about a .5v drop.I basically checked if there was a short and one seem to give me a reading in both directions, i believe on the diode side. Could also be because its in circuit so a false reading

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 04:41:42 pm
content: Can you post pictures of the section which includes optocouplers from both sides of the board?

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 05:23:46 pm
content: Sure thing. Ok so the bottom one is the one im most suspicious about. When I check the diode side I get readings in both direction also when checked on an oscilloscope it has a different wave form. The bottom one has a shark tooth with a exponential decay then repeats. The middle has a more uniform shark tooth wave. and the top I believe has a shark tooth wave but its too small of a voltage change for my scope to show properly.

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 05:24:41 pm
content: Heres the others

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 05:36:45 pm
content: actually now looking at it closer it has a diode bridging the two connections on the LED side. Still the diode side has a value when testing both directions.

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 05:43:35 pm
content: Is TO-92 near optocouplers a TL431? Whats is written on it?

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 05:57:07 pm
content: It is a AZ431 or AZ-AE1. Those are what is written on it.edit Yes basically the TL431.

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 05:58:59 pm
content: Can you also do a light from back picture (x-ray type), to get good visibility of tracks of this section?

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 06:19:47 pm
content: here you go

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 07:13:11 pm
content: So the one closest to the board edge is for feedback. Can you measure voltage with a multimeter on cold and on hot side while it is running? Negative lead to one pin and positive to another. Don't touch with your fingers, it may be on high voltage on a hot side.

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 07:22:41 pm
content: Also, can you identify U5? And why does it look so messy in the picture? Is everything soldered good?

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 07:34:11 pm
content: cold side reads .746v annd hot side reads about 90mV then increases to about 300mV then repeats.And yes its fine from looks. I believe it is covered in some kinda of clear protective stuff not really sure but other parts have it on it.

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 07:46:46 pm
content: I am not really sure what it is the numbers are so small haha

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 08:08:04 pm
content: What happens if you solder together (short) the two pins of HOT side of that optocoupler? Does power supply give any output voltages, 5, 12V when turn on?

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 08:14:25 pm
content: Are you asking if the +5 and +12 pins give out those voltages?

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 08:18:08 pm
content: Yes. If you short optocoupler on a HOT side, how does power supply behave? Does it give any outputs? Is it different to what it gives normaly?

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 08:28:50 pm
content: Shorting it results in no output voltages

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 08:48:48 pm
content: I would also like to mention after getting a better multi meter the readings of the +5 and +12 pins are 4.7 and 11.2 and stable.

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 09:04:42 pm
content: Quote from: pieshower on April 22, 2020, 08:48:48 pmBut you said, that on scope it is saw tooth waveform? So it means your better multimeter just does better averagingOne more fun test. Remove short on the optocoupler - back to normal. Connect scope ground clips to ground (the ground of outputs connector, you can solder a few centimeter wire extension to have easy clip on) and connect both channels to the COLD side of optocoupler. Post how it looks both channels side by side.

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 09:38:16 pm
content: Ok so bad thing happened I accidentally shorted one of the bridge rectifiers pins to the heat sink. I was trying to measure the Voltage like a noob and was reckless. Its grounded so I dont think anything is bad. Heres the scoped optocoupler.Like Im still getting the same readings so I think its all good. haha

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 10:22:29 pm
content: Ok, so when you shorted optocoupler on HOT side this simulated a fixed feedback signal that output voltage is already above nominal. Power supply was behaving correctly and did not push that voltages, so they remained at zero. That means that on HOT side the feedback somewhat works.Now in normal operation it seems to not get enough feedback, so it thinks that output voltage is still low, still low, still low, so it pushes more and more, but it is actaully already too high and separate circuit (over voltage protection) kick in and does emergency shutdown.Your scope picture seems suspicious to me. I never had such a power supply in my hands, there is no schematic, so I'm just judging from general knowledge. For example it seems, that the difference between CH1 and CH2 is never more than ~600mV, which is not enough for a typical optocoupler to turn on.I would say you have twi choices. Order optocoupler and TL431 (they should be cheap), replace and see if it helps. Or remove them from board and test if you feel enthusiastic about learning stuff.There is also some diodes involved in feedback on a COLD side.

author: aqibi2000
author_rank: Regular Contributor
timestamp: April 22, 2020, 10:28:30 pm
content: You mentioned the output voltage rails fluctuate, could you capture this shown on the oscilloscope on say a 100ms time base?In your case you don’t even have a a minimum load connected so it makes things even worse.You can always test the optocoupler out of circuit, using very few components to build an actual circuit.A real fly back switch mode power supply voltage output does have some level of noise on the output, article is a tad exaggerate by analog deviceshttps://www.tablix.org/~avian/blog/archives/2018/05/on_the_output_voltage_of_a_real_flyback_converter/

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 10:53:57 pm
content: I will definitely remove them and test. I am loving this and I appreciate you helping me for I am learning so much on hand stuff. This stuff is freaking cool and fun.I tested the diodes in circuit and they appear to be in working order. Would I have to take them out for a better reading? I know if theres a lower resistance path to the other meters lead then it would take that path around the diode.The yellow is one of the +5v pin and the blue is one of the +12v pin.

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 11:04:49 pm
content: Just noticed you said 100ms so heres 80ms

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 11:18:34 pm
content: For TL431 you can build a test circuit. In this circuit TL431 should give 2.5V regulated output, like it does in the simulation below.Battery top side is positive, down side negative (use bench supply).

author: pieshower
author_rank: Regular Contributor
timestamp: April 22, 2020, 11:20:21 pm
content: What program is that?

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 11:21:46 pm
content: NI Multisim 14.2

author: Manul
author_rank: Super Contributor
timestamp: April 22, 2020, 11:40:16 pm
content: And optocoupler is basically a LED inside which shines on a transistor and that transistor turns on. So on a LED side (COLD side of your power supply) with diode mode you should measure around 0.8 - 1.2V with forward polarity, and nothing with reverse polarity (removed from board). To test fully, build a circuit. If there is no current to LED, transistor is basically open. If you give current to LED, transistor turns on and pulls down the voltage. Don't forget resistors

author: pieshower
author_rank: Regular Contributor
timestamp: April 23, 2020, 12:05:36 am
content: Yes I am familiar of what it is and how it works. I will try this now. thank you

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 06:16:29 pm
content: Ok so I tested the TL431 At it's working just fine. I tested all the optocouplers and they all read 3.16 M Ohms then nothing with lead reversed and about 243mV except for the one for feed back. It measures about 2.9 M Ohms and nothing with the lead reversed and about 230mV. Can that small of a difference effect the outcome voltages?

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 07:09:27 pm
content: Ok so you may be on to something. Basically what I did was rearrange the semibad one with the other one. I was getting about 4.5v to 4.9v for the +5v and 13v for the +12. THEN AHHHHHH I acidentally shorted the 2 +12v pins with my multimeter. And all was lost. Now im getting lower voltages from different pins. So Im guessing since one of the couplers is bad its affecting the output of the circuit its not attatched too. My guess its the system power circuit but I'll trace back to confirm.

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 07:15:43 pm
content: Im also getting voltages on the +5 and +12 rails even without shorting the 5VSB to the STB rails

author: Manul
author_rank: Super Contributor
timestamp: April 24, 2020, 07:23:09 pm
content: Are all three optocouplers same part number? What is that part number? Megaohms of optocoupler really means nothing. What are these milivolts? How did you measure these?

author: Manul
author_rank: Super Contributor
timestamp: April 24, 2020, 07:25:29 pm
content: What was forward voltage drop of LED side of feedback optocoupler?

author: aqibi2000
author_rank: Regular Contributor
timestamp: April 24, 2020, 08:44:24 pm
content: Test the optocouplerYou don’t need 18V just any dc voltage on that side is ok.

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 09:28:44 pm
content: I did test them. I pulled each out of circuit and set up a testing circuit like in the picture you showed me. On the annode side of all three we got about a 1.13v drop for each one. and on the Transistor side we got about 240mv. Except for one of them which got about 230mV.I will say I did it without the switch for it was difficult to measure the the voltage while trying to push the switch (only had a button). But I just did my test as if it was constantly on.

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 09:30:32 pm
content: Sorry if my wording is hard to understand haha bare with me. And yes they are all the same part number. 817-b. Ive been reading their datasheet for any useful information.

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 09:49:31 pm
content: Also what I did was resolder them in different orders than they were originally. I was still getting the over voltage switching but the +5 and +12 pins had high voltages than before. with the +12v having a 13v output. And when I connected my multimeter leads to the ground and the +5v and +12v pins the clicking seemed to stop.

author: Manul
author_rank: Super Contributor
timestamp: April 24, 2020, 09:58:43 pm
content: All is fine, but if you measure something, please also try to state the conditions of measurement, just to be sure that we talk about same thing.And without LED current, they all showed 5V on transistor side?Optocouplers seems ok based on your measurement. That small difference should be well within normal variantion.What was suspicious in the first place, is that the voltage on the feedback optocoupler on a working board seemed too low. It looked like well below forward voltage of the LED. But on another hand it was not clear where exactly is 0V for each channel on your scope picture.Could you repeat that and set both channels to zero vertical position, so they both overlap and can be compared more accurately?

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 10:22:27 pm
content: Of course. Ok so whats happening now since I changed which one was in feedback place. Its a tooth form wave completely different then last time. Every now and then there will be a much bigger spike resulting in a bigger tooth. Also when I first plugged it in it was uniform but slowly increased in mV and became very fuzzy like noise or something. I cant get it to reproduce it.

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 10:28:17 pm
content: Heres what the middle one looks like after probing.

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 10:31:38 pm
content: and heres the top optocoupler

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 10:33:18 pm
content: And then after like 2 minutes the top one smoothed out to this with a spike every now and then.

author: Manul
author_rank: Super Contributor
timestamp: April 24, 2020, 10:49:28 pm
content: Well, I have no idea anymore. I suggest to try to come back to the original condition.

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 10:50:23 pm
content: yeeeeaaahhh Im even more puzzled. I will just resolder them in original order.

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 10:52:52 pm
content: Do you think it could just be a bad egg spoiling the rest of them?

author: Manul
author_rank: Super Contributor
timestamp: April 24, 2020, 11:04:46 pm
content: If they are all same and work ok in testing circuit there should be no difference when you switch them. Maybe it is some other factor, which you did not notice. How about that shorting of 12V rail? You said that things changed after that? To me, honestly, it looks like things are going out of control with you power supply

author: Manul
author_rank: Super Contributor
timestamp: April 24, 2020, 11:08:31 pm
content: Also you said, that for some reason it started being ON without a jumper? But you do not mention if you fixed that. I mean, if it is getting more and more broken it will be hard to keep up

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 11:10:01 pm
content: UGGh Its going wacky. I think im going to just try and draw a schematic for it. Any newbie tips for that?Yes it was displaying numbers let me recheck. But they were low like 1v to 2v.

author: pieshower
author_rank: Regular Contributor
timestamp: April 24, 2020, 11:16:27 pm
content: The other pins aren't getting any thing still when unshorted but the 5VSB is now down to about 2.5v. I really think it has to do with one of them not working properly and since I switched their places different parts are not behaving as they should be.

author: Manul
author_rank: Super Contributor
timestamp: April 24, 2020, 11:22:22 pm
content: Ok, so switch back, how it was and lets see. Draw schematic of power supply? That is hard, recomended to not even try. Some small parts of it - maybe.

author: Manul
author_rank: Super Contributor
timestamp: April 24, 2020, 11:52:48 pm
content: I marked optocouplers functions to be clear (hope to be correct).EN (enable) - when you give 5V to STB, this optocoupler is turn on to give signal to another side to start.OVP (overvoltage protection) - if output voltages rise too much and reaches a threshold, this turns on and gives signal for emergency cut-off.FB (feedback) - this starts to turn on when outputs are near nominal voltages and gives feedback for regulation.

author: Manul
author_rank: Super Contributor
timestamp: April 25, 2020, 04:05:28 pm
content: Actually, I think I have pretty good idea of what was original problem. But you need to get back to the original condition:1. 5VSB is correct and stable2. Power supply is running only when you connect STB to 5VSB

author: pieshower
author_rank: Regular Contributor
timestamp: April 26, 2020, 04:29:25 am
content: Ok I fixed it back to its original state. Solid 5.2 volts for 5VSB when not shorted and no power to the +5v and +12v rails. And when the 5VSB is shorted to STB, I get 4.7v for +5 pins and 11.2 for +12v pins.

author: pieshower
author_rank: Regular Contributor
timestamp: April 26, 2020, 04:41:58 am
content: Also there appears to be a strange connection between these 2 pins on the back side that I can't or don't see how they can be connected. I was just testing around with my continuity meter.

author: Manul
author_rank: Super Contributor
timestamp: April 26, 2020, 05:37:45 pm
content: I got interested, because it looks to me a suspicious implementation of the feedback loop.With 5VSB and STB NOT shorted (with just standby 5.2V present), measure voltages of marked points. Negative lead to GND.

author: pieshower
author_rank: Regular Contributor
timestamp: April 26, 2020, 08:16:33 pm
content: ok so in order as listed:1. 5.18v2. 12.67v3. 5.17v4. 2.5v

author: Manul
author_rank: Super Contributor
timestamp: April 26, 2020, 08:44:26 pm
content: So there is no 12V output on the connector, but there is 12V on point 2?

author: pieshower
author_rank: Regular Contributor
timestamp: April 26, 2020, 09:08:43 pm
content: yes. I just continuity test on this mosfet and it appears to be shorted. It is a M7018AD fast switching mosfet. I have a picture of it but the internet is being a bit slow.

author: Manul
author_rank: Super Contributor
timestamp: April 26, 2020, 09:33:01 pm
content: We talk something different here. Anyway, you may try to lower the output voltages and see if psu gets stable. Find a 47K (kiloohms) resistor and connect as shown.

author: pieshower
author_rank: Regular Contributor
timestamp: May 01, 2020, 04:15:50 pm
content: Hello sorry I've been stuck doing finals this week. Im going to work on it some today. I do not have a 47k ohms resistor I do however have 100k, will this work?

author: Manul
author_rank: Super Contributor
timestamp: May 01, 2020, 04:55:57 pm
content: Off topic: sometimes when beginner people are fixing power supplies and they suddenly disapear, I get bad feelingI guess I do have some fear, that if someone hurts himself, I may be somewhat responsible, because I was helping or encouraging. In real life I actually strongly discourage my friends for doing such things if I have doubt about their knowledge or carefulness.Anyway, use two 100K resistors in parallel, that will be 50K total.

author: pieshower
author_rank: Regular Contributor
timestamp: May 01, 2020, 05:09:24 pm
content: Haha Yes I understand. I had the same thought that I should probably check in. Ok will do that now.

author: pieshower
author_rank: Regular Contributor
timestamp: May 02, 2020, 12:08:28 am
content: ok so after connecting a resistor as you showed the output voltages read as shuch. 5VSB and STB are at 4.3v, the +5V are at 4.3v, and the +12V are at 10.3v.

author: jackthomson43
author_rank: Contributor
timestamp: May 02, 2020, 07:07:56 am
content: Yeah looks like problems in capacitors as Hitachi power supply board uses cheap and crappy CapXon capacitors.You should get your hands onMicrocontrollerbased ESR meter and measure equivalent series resistance of these capacitors.

author: Manul
author_rank: Super Contributor
timestamp: May 02, 2020, 04:32:07 pm
content: So how these voltage look now? Is there still saw tooth? What is min and max points?

author: aqibi2000
author_rank: Regular Contributor
timestamp: May 06, 2020, 11:21:46 pm
content: I take it this tv is fixed and up and running

author: pieshower
author_rank: Regular Contributor
timestamp: May 07, 2020, 02:45:53 pm
content: Sorry guys I've still been busy finishing up some finals. I back and ready to work on this more.Heres what the outputs look now through the oscilloscope after putting in that 47k ohm resistor. Yellow is the +5V rail and blue is the +12V rail.Again, sorry, I know I should give word but recently the only things on mind were my finials haha. hate school.

author: pieshower
author_rank: Regular Contributor
timestamp: May 23, 2020, 05:05:16 pm
content: UPDATE* I just got some parts in, this virus got postal slowed to a crawl. Testing them out and comparing them to old parts. This is probably a dead chat but I am still very curious if anyone is still interested in helping me tackle this problem. Also I just reread what was asked and I failed to provide the voltages of the output. I will do that as soon as the parts are replaced. Im going to replace the CapXon caps as well but on account of how slow the mail has been lately that's gonna be a bit. To Manul, if you are still interested I would love and appriciate the help, but I can understand that working with a newbie can be quite frustrating, especially when they disappear haha. Believe me I am still very interested in this. But again thank you very much for all that you have shared with me.