Another TV Repaired!

This Freegle donation is a 32-inch JVC Smart television with LED backlight. The set was powering up, but no picture, so the backlight was suspect. The very bright torch trick revealed a picture lurking in the murk, so the set was worth repairing. The power supply was putting out 94-volts to the backlight which seemed excessive, but before I could investigate further I managed to short something and the output dropped to just 30-volts. I decided to take a chance on a replacement power board off eBay and while that was on its way I dismantled the television to take a look at the LEDs. The diode test setting on my DMM (digital multi-meter) was reading open-circuit, but across a lot of LEDs this doesn't always mean anything.

Carefully taking the thing apart and putting the LCD panel to one side, I discovered that there were 22 LEDs, but one had already been removed and soldered over so someone had previously tried repairing the set. The problem with this shorting-out approach is that you are then putting slightly above 3-volts across the remaining 21 LEDs and putting them under stress. Since the power supply had been giving an output of 94-volts instead of 66-volts (22 LEDs x 3-volts each), I figured something had gone badly wrong with the power board and it had fried more of the LEDs.

It turned out that by testing each LED individually with a battery and resistor (remember testing old Christmas tree lights?) I found a further 3 LEDs were open-circuit making 4 to replace in total. I used the Minicraft grinder to remove the broken ones and then soldered short strips from a salvaged backlight over the top (see top photo). A bit ignorant, but you can't see this once the set is repaired and more importantly it works. The photo above shows one of the salvaged strips with the copper exposed with a bit of sand paper ready for soldering.

The power board arrived and after checking it was giving out 66-volts and putting everything back together, the television is working fine and I was able to set up the Smart features Wi-Fi and Netflix. Total cost £10 for the new power board, but would have been zero if I'd taken the time to fix the old one (been less lazy). Next time!