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I received SmallHD 5" display which was broken by supplying 14.4V by a mistake. It runs on 7.2V typically. The monitor is fine, just the backlight went bad. I replaced TPS61180 right off the bat but this didn't fix the issue. Right now I'm getting 15V on the output which is too low to drive 14 LEDs (7 in series, 2 in parallel).

Diagram

I checked all caps and they seem to be fine. D1 looks good to me (can it affect the output voltage?).

I'm out of ideas for this one. The backlight is flashing once at boot and then it's off. I tried replacing the IC a few times, it's not the IC causing the problem. Do you have any idea or clue what should I check next? I don't know how LED drivers work so I hit the wall.

BTW. The part marked as Optional is not included in actual circuit.

Maciej Kobus
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    I've encountered multiple diodes over the years that still measured correctly after "receiving a hit" but had become slower (long reverse recovery), wreaking havoc in SMPS. Won't hurt to try and replace it. Some of the LED's themselves might've been damaged too of course, tripping some overcurrent protection in the chip. – Unimportant Nov 12 '20 at 22:49
  • Replaced D1 and stil one blink and then off. I also built 7 in series/2 in parallel LEDs to rule out broken LEDs in the panel itself. The effect is the same with original panel and my LEDs. – Maciej Kobus Nov 12 '20 at 22:58
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    The datasheet contains a section "OVER-CURRENT,OVER-VOLTAGE AND SHORT-CIRCUIT PROTECTION" that explains the conditions that make the chip shutdown (without self-restarting). You can investigate those conditions. – Unimportant Nov 12 '20 at 23:14
  • Maybe this is indeed some kind of protection kicking in but I exchanged original LCD panel with my LED contraption and the issue is the same. So this is definitely not any kind of short on the LEDs. Something is bad in the backlight circuit. I replaced D1 with a diode from different LCD, maybe it's not fast enough too. I'm not an expert but where is switching happening? I assume it's on Vo. – Maciej Kobus Nov 13 '20 at 09:25
  • I was suspecting C2 was partially shorted, pulling it to the ground and lowering the voltage. Desoldered it, no effect. I will replace ISET resistor next as this is the next thing that can directly affect the output. – Maciej Kobus Nov 13 '20 at 09:26
  • The switching is happening at the SW pin. When the MOSFET inside the chip is switched on, SW will be pulled to PGND. This puts the inductor in parallel to the power supply, "charging it up". When the MOSFET switches off, the inductor becomes a current source in series with the power supply, which is what generates the higher voltage. – Unimportant Nov 13 '20 at 10:05
  • Okay, maybe this is indeed a diode issue. I will try replacing it again with a different one. Thanks for the explanation. 14.4V seems to be up to the spec for TPS61180 so I don't think it was killed in the process. Most likely a passive element was not rated for such high voltage. A bad diode seems to be reasonable explanation. – Maciej Kobus Nov 13 '20 at 10:23
  • Sorry for spamming: Things I've checked: replaced the IC multiple times, replaced D1 with many different diodes, replaced C2. Always the same effect - single blink and then off. I tried original LCD panel, LEDs contraption (7 in series, 2 in parallel), backlight from different LCD. It doesn't change anything. Does anyone else have an idea what I should do next? To me it looks like some kind of protection is kicking in but I don't know why. – Maciej Kobus Nov 13 '20 at 21:21

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