LH70BVPLBF/ZA samsung 700DX2 power issue

[Tonycjr23]

Hi guys, this is my first post so ill be as descriptive as possible, I have a display that was given to me, the model number is LH70BVPLBF/ZA
I realize its a monitor, not a tv, it was given to me by my place of employment because they didn't think it was worth troubleshooting and repairing given the cost of newer cheaper units but me and my mechanical brain says wow, a 70 inch dumped on me for nothing. BUT OF COURSE!!

anyway, plugging it in and hitting power leads the unit to cycle on, its a display that's got cooling fans in it so it was designed for 24/7 usage like the Samsung site says, but all the fans will kick on, the display will light up in full, theres no indication of backlight burn out just by a look at it when it does, and then it will power off. THEN it will re-cycle on and repeat the process 2 more times before kicking off then go unresponsive until I hit the power again, and every time it kicks off I hear a click from one of the 2 power boards. knowing what I know from the basics is that the screen isn't damaged and it powers on so its half way there, and the main board doesn't look fried after checking and re checking for bulging caps or burned mosfets, so my question is, where would YOU start your trouble shooting and how? and where would I be able to find the parts needed to repair this thing.

tools at my disposal are a multimeter and my determination to use this thing and prove my wife wrong that its not junk and worth repairing.

thanks guys, I can supply any and all pictures and video from my phone later on if needed to help you help me

[heavymachines]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

Pictures

[Tonycjr23]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

I'm operating on my phone right now but last night I seem to have narrowed down a cluster of caps that seem to be making the noise I'm describing, it's almost like the sound that firewood makes when it's thrown into a fire without curing the moisture all out of it.

Does anyone have an idea as to how I can post the pics I've taken from my iPhone photo gallery or do I have to upload them to flicker or a photo storage place, it won't allow me to upload pics without a URL

[Tonycjr23]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

The first picture is the board that is suspected to be the trouble, it is the one making the noise yet just by a quick view it doesn't look like any caps are bad

The second pic is the group of caps I've narrowed the noise down to, does anyone see anything out of the ordinary or suspect to cause trouble?

[Tonycjr23]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

I figured out how, working my way through the forum little by little, electronics repair intrigues me so I will be posting a lot and have a lot of questions as silly as some may be

[heavymachines]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

Are u sure the noise isn't coming from surrounding transformer or inductor, does inductor feel warmer then it should?

[Tonycjr23]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

I'm not able to Check temperature because it will not stay on for more than 2 seconds, but is the noise anything I should consider suspicious?

[Tonycjr23]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

Is the hissing even a problem I should worry about?

[cpt.charlie]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

Are you sure the clicking noise isn't coming from the relays?

[Tonycjr23]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

The clicking I'm not too worried about, I know relays make clicks, it's that hissing like its a bad cap somewhere that I can't see, do they ever leak from the side with the leads?

[cpt.charlie]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

Check the rectifier and try to measure if the output voltages are present at the connector.

[Tonycjr23]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

How would I do that safely? I realize that one crossed trace or a wrong probe tap somewhere and the units cooked, plus the mix of high voltage I would like to not zap all of it, or myself, can a rectifier be tested with the board removed? And the capacitors? Can they be accurately tested without the board installed? I feel like they're all basic questions but they're legitimate questions, I want to do this right, thank you for all the help in advance

[Tonycjr23]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

So a small update, I got down to the capacitors and they were all metered out to be good. I started pulling the jumpers between components and I came to the inverter controllers, with all of them plugged in the set turns off, so I started unplugging them one at a time and pressing power, sure enough one of them finally made the set turn off with being connected and when disconnected the set stays on fine but no backlight. I ordered a replacement on eBay that identically resembles the board I pulled except for a few numbers on the serial number, but everything else is identical. I'm not positive that the board swap will fix it but I'm praying it does and is the practice of mismatched serial numbers safe? Everything on the board, print for print matched up but the yellow paper tag. I'll keep you posted

[cpt.charlie]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

You can check the rectifier with your DMM in diode mode (power removed to the board), in fact the 3 pin rectifier is just 2 diodes "front to front"

[Tonycjr23]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

well I unplugged each inverter board and plugged them in one by one until the set turned off, turns out it was the number one board that was causing the fault and causing it to shut off. Is that typical of an lcd monitor where an inverter board will cause it to shut down entirely? what are the chances of that being my only problem and it not being either the circuit from the board feeding the number one or possibly being the ccfl bulb itself? the monitor is considered digital signage so its made for 24/7 use. it has cooling fans for each individual board so I have my fingers crossed that the inverter was the only issue

[cpt.charlie]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

When a lamp is almost burnt or even shorted to chasis, the HV inverter hould have overcurrent protection and keep the rest of the set "working", the hissing noise could be the inverter, disconnect the lamp and check if the monitor keeps shutting down, maybe the problem is just a dead CCFL lamp specially if it has been running 24/7 for a few years..

[Tonycjr23]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

I've concluded that the ccfls are actually bad, I can get a picture with the inverters all unplugged but no backlight, my goal now is to replace them all with an led array, is this a futile attempt at resurrecting this thing? How easy is it to replace them with an led array, it's a pretty sweet unit judging by the others I've seen still operational. Any tips in advance to adapt this thing to led's would help greatly, thanks in advance

[cpt.charlie]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

It's gonna be quite difficult to find a suitable LED replacement for a 70" monitor.

[Tonycjr23]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

Well honestly I'm not above turning it into a light box with a separate driver to power the led's without having to tap into the existing power. but please save me a lot of aggravation and tell me why

[cpt.charlie]

Re: LH70BVPLBF/ZA samsung 700DX2 power issue

Most kits for ccfl to LED conversion i've seen are for "small" screens like 19"- 24", finding a proper kit for a 70" monitor will be quite challenging, maybe it's easyer to locate the right replacement for the CCFL lamps.

https://www.aliexpress.com/item/10PC...716918823.html