Author Topic: Hitachi TV will not turn on and no stand by LED (Read 9490 times)

pieshower · « **on:** April 18, 2020, 09:32:08 pm »

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?

Manul · « **Reply #1 on:** April 18, 2020, 09:55:45 pm »

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)?

pieshower · « **Reply #2 on:** April 18, 2020, 10:18:53 pm »

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 11v

Im 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.

Manul · « **Reply #3 on:** April 18, 2020, 10:36:02 pm »

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.

floobydust · « **Reply #4 on:** April 18, 2020, 11:25:27 pm »

Hitachi 65" LE65K6R9 50326502000060 power supply board uses cheap crappy CapXon capacitors, which I would test and replace.

pieshower · « **Reply #5 on:** April 19, 2020, 12:33:06 am »

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.

Manul · « **Reply #6 on:** April 19, 2020, 12:50:24 am »

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.

pieshower · « **Reply #7 on:** April 19, 2020, 01:05:13 am »

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.

Manul · « **Reply #8 on:** April 19, 2020, 01:24:08 am »

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.

pieshower · « **Reply #9 on:** April 19, 2020, 01:33:21 am »

Ah I was still on diode tester mode. All the pins read 5v.

Manul · « **Reply #10 on:** April 19, 2020, 01:49:33 am »

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?

pieshower · « **Reply #11 on:** April 19, 2020, 01:59:23 am »

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.

Manul · « **Reply #12 on:** April 19, 2020, 02:15:51 am »

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.

Manul · « **Reply #13 on:** April 19, 2020, 12:50:55 pm »

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.

pieshower · « **Reply #14 on:** April 19, 2020, 03:18:10 pm »

Yes I was thinking it was because the cable was connecting the two pins. I will do that now.

aqibi2000 · « **Reply #15 on:** April 19, 2020, 03:28:49 pm »

If this is a LED tv then disconnect the backlight.

pieshower · « **Reply #16 on:** April 19, 2020, 03:35:04 pm »

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.

Manul · « **Reply #17 on:** April 19, 2020, 04:48:37 pm »

Is this with backlight disconnected? No loads on power supply? Then it seems it is bad. Could be electrolytics, but not 100%.

pieshower · « **Reply #18 on:** April 19, 2020, 05:10:53 pm »

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.

pieshower · « **Reply #19 on:** April 19, 2020, 05:36:26 pm »

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.

Manul · « **Reply #20 on:** April 19, 2020, 05:41:04 pm »

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.

pieshower · « **Reply #21 on:** April 19, 2020, 05:44:18 pm »

I do have a signal generator and a oscilloscope.

Manul · « **Reply #22 on:** April 19, 2020, 05:46:50 pm »

Manul · « **Reply #23 on:** April 19, 2020, 05:49:01 pm »

100 kHz is usually a standard if you want to compare to the datasheet values.

pieshower · « **Reply #24 on:** April 19, 2020, 07:43:39 pm »

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


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Author Topic: Hitachi TV will not turn on and no stand by LED (Read 9490 times)

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