LG 42PT353K main board heat issue - smd diode identification

[tn245]

I'm working on this LG - picture+sound cuts out when warm. Test patterns work when problem is present. Localised heating of main board reproduces the problem. I was thinking probably common LG processor BGA solder issues but with targeted heating I have narrowed it down to one SMD diode. Without fail, heat up that component, it dies, cool it down it comes back.

Diode is D400 as pictured. SOT23 package and markings A3 16. I'd like to try replacing it. I have found a few options with marking A3 in SOT23 - mainly dual switching diodes. Anybody have any suggestions what to replace with?

Thanks for any help!

** EDIT - it's not the diode. Think it's the cap next to it I was inadvertently heating as well due to proximity. Wish I could delete threads. Gonna try replacing that cap then

[petehall347]

Re: LG 42PT353K main board heat issue - smd diode identification

is it soldered in ok ? some of the soldering on that board looks suspect

http://www.s-manuals.com/smd/a3

[tn245]

Re: LG 42PT353K main board heat issue - smd diode identification

Yeah, I already tried retouching the solder. I think it's actually the cap next to it actually. Really should be more thorough before posting.

[petehall347]

Re: LG 42PT353K main board heat issue - smd diode identification

might even be something on the other side of the board .. had a teaser like that a while back

[flocko]

Re: LG 42PT353K main board heat issue - smd diode identification

diode marked A3 = motorola MMBD1005LT1 hope this is of help

[ReeceyBurger123]

Re: LG 42PT353K main board heat issue - smd diode identification

Diode could be leaky and getting warm I hate these Lg mainboards utter shit, also after you change it dont forget to add a fan to the cpu or a better heatsink with better thermal interface.

[tn245]

Re: LG 42PT353K main board heat issue - smd diode identification

Going to investigate that cap because with more focussed heating it seems to be the culprit now instead of the diode. Nothing on the other side of the board in that spot. Meanwhile I'd love to see some examples of cooling mods for these mainboards. Anybody got pics?

[tn245]

Re: LG 42PT353K main board heat issue - smd diode identification

So it was the cap. Measured out of circuit the capacitance would go way out of spec when heated even slightly. Replaced it and the TV is working great with no heat issues. On ReeceyBurger's suggestion I have put a heatsink and 12v fan on the cpu - attached with thermal silicone and connected to the 17v supply via a 10v regulator. Runs stone cold.

[vinceroger69]

Re: LG 42PT353K main board heat issue - smd diode identification

Thanks for the update and adding the fan and heatsink hopefully will make the set last a lot longer.

[ReeceyBurger123]

Re: LG 42PT353K main board heat issue - smd diode identification

Good man I like the work, welldone

[tn245]

Re: LG 42PT353K main board heat issue - smd diode identification

Thanks! To be honest the fan does have a bit of a whine once it gets up to speed, so I'm thinking about dropping the voltage a bit more.

[jondoe]

Re: LG 42PT353K main board heat issue - smd diode identification

Excellent use of the hot glue gun!