Chosen Solution
I just picked up this Toshiba 50L1450U to repair. It does not power on, there isn’t even a stand by light. When I check the Power Board I see no issues, the voltages match the markings and the voltages follow through to the main board connector. Is this indicative of a bad main board? I’m not even sure what to check on the main board to diagnose. LED strips tested okay as well. Other potentially not relevant tid bits : -The power cord was a polarized cord/connector and somebody shaved down the square side to make it fit like a non-polarized connector. -the boards are mounted to the plastic backing panel rather than the metallic TV casing. Huge PITA during removal because the boards have to be removed and then somehow re-affixed to the back of the tv for proper grounding which isn’t entirely possible due to the mounting orientation. Thanks for the help. Update (07/08/2020) These are the circuit boards, apologies for the quality. Basically the power board powers the LEDS directly and the mainboard. From the main board there is a harness to the standby light and the t-con. It’s actually quite minimal. I measured everything I knew how to measure - 5v, 12v, ground. I don’t know how to measure “BLON” or “DIM”
Update (07/09/2020) @jostewcrew I removed the shield but this doesn’t look like the traditional t-con setup I see in other TV’s. No ribbon cables. It looks like the cable is going directly into the LCD boards, I see no fuse. Attaching a photo momentarily. Out of curiosity I tested the Standby/IR LED with my LED tester. At first I got it to light up no issues but then as I continued testing I could NOT get it to light up again. Only a very dim flicker.
Update (07/08/2020) Ok I’ve tried removed some more panels and it looks like the tcon is integrated with the buffer boards. I didn’t see a fuse but will continue to investigate.
<—This website does not play nice with picture uploads. Preview shows image, no image posts. Try to post as question update - website is not responsive. Try to post picture from phone, photo shows as text. Super glitchy. Update (07/17/2020) Power board model #
Update (07/22/2020)
@jayeff @jostewcrew Okay I received the power board from ebay and it was curiously missing the main fuse. So I swapped in the fuse from my other board and immediately upon plugging in the power cord the fuse blew. I am thinking this replacement power board may have a short which might explain the missing fuse in the first place. What do you guys think? I’m going to buy some more T4A fuses and try again.
from your testing: your power supply is generating the required voltages and are holding them steady to feed to the main board. the main board from there supplies its other required voltages and feedback signals for the logic function of the unit. i.e., the blon voltage comes from the main board to tell the power supply to kick on the backlight circuit. for the back lights to come on, it requires 3.3v which is supplied by the main board if functioning. ( you can test backlights in your case by disconnecting the cable to the main board and jumping pin 12 and 13 on the power supply. (pin 15 is for dim, which is fed by pwm from mainboard. this may also require 3.3v , if backlight doesnt turn on with 12 and 13, add in pin 15..this will be at full brightness, so test only and disconnect.) this will close the signal that was supposed to be from the main board and trick the power supply into turning on the backlights) in addition to this, the standby indicator light also is fed by the main board. it is stepped down from the 12v fed by the power supply (which is steady) and created by the main board to feed the required voltage to the circuit. the fact that you have no light is another clue. i was trying to test voltage at the fuse to the tcon because its voltage is also supplied by the main board. if it wasnt present, the mainboard is not creating the rail, again pointing to its failure. i believe changing out the main board is going to solve your problem. here is a link to a vendor that is reputable and has one in stock: https://www.tvpartstoday.com/75036660-To… if any further assistance is needed, please update here and let us know the resuts.
