Power for LED backlight

Find a replacement...

https://www.ebay.com/b/Led-Backlight-Strip-In-Computer-Monitor-Replacement-Parts/168068/bn_7022233876

https://adaptivepower.com/Resources/Documents/APS_App_Note_LED_Driver_Testing.pdf

https://www.walmart.com/ip/Universal-26-65-inch-LED-LCD-TV-Backlight-Driver-Board-TV-Constant-Current-Board/916520967?

Yes, I thought 5.8 Volts was really high too. The chart Rixter had was more in line with what I remembered. So next week in the shop I'll check the amps on the larger display that still works and wait for the replacement LED strips to come in. I may even have a capacitor in my spare parts to throw on for a trial.

The voltage may make the LED conduct forward and turned on, but It is the proper amount current that makes the LED glow brighter..

That is usually a blown electrolytic capacitor on the main board that causes the back light to go dark. Pull the board and look for puffed up caps and just replace them.

I have also encountered broken solder joints on many boards using lead-free solder for through board solder joints. I don't thing the new alloys are as good at preventing tin pest as lead solder.

I sympathise with your predicament as I work on circuits often. I have found that low value electrolytics fail more often then the higher value. My method on multilayer boards is to remove the suspect electro by cutting off close to the board. The leads can then be unsoldered and the holes cleaned out with a desolderer, a solder sucker or desoldering braid.

I have found that the non lead solder tends to form dry joints and fail in what we term frogs eggs, where the solder forms into clumps of silvery grey speckles.

Surface mount capacitors are a whole different kettle of fish but they can be replaced if one has the right heating gear or very fine soldering iron tips. As for LEDs I have come across a few in strings where one may become open circuit or worse still short and take a few more out from excess current.

Happy repairing.

As Rixter has stated, LED's are current-driven devices. If you are going to drive them from a voltage source (vs a current source), you should always have a current limiting device in series, such as a series resistor. Otherwise, you risk exactly what happened, you burn out LED's because the max forward current is exceeded.

Your best bet would be to repair the existing current driver in the monitor, so that you will still have adjustable brightness settings from the front panel. If you can't fix the existing driver, look for a constant-current source supply that will output the correct current, in the voltage range needed for the LED strips.

Tom