LG 42LB5D, 42LB5DF-UL, 2008-01, Power On Issue, Replaced PS Caps

[bcstedt]

LG 42LB5D (42LB5DF-UL) from 2008-01, unit is in good shape and no obvious heat damage or cracked solder on the boards.

Problem:
On first power-up the power LED flashes green about 18x and then stays solid. No backlight or image is present. Click power button, wait 10s for a click and the LED turns red. Wait 1-2s and hit power again and maybe it'll power up fully after 6 green flashes. If it doesn't light up on the sixth flash then the cycle repeats.

It seems that if the mainboard power is left on for a few minutes (solid green power, no backlight, no image) it will often power up OK. If you constantly power up/down after 6-flashes then it never seems to catch.

Once the unit is running it seems OK aside from some mild burn in and a bit of colour ghosting.

The power board has been gone over and six puffed caps were replaced. I've been going over caps on the mainboard and checking connectors / connections but nothing obvious is coming up yet.

[bcstedt]

Power Supply w Bad Caps
EAY32731102
https://www.shopjimmy.com/lg-eay3273...r-supply-unit/

Mainboard (some caps getting bad, Samyoung,etc)
EAX38059702
https://www.shopjimmy.com/lg-42lb5df...11-main-board/

Inverter Boards (caps check out OK)
https://www.shopjimmy.com/philips-99...-inverter-kit/

[bcstedt]

Inverter Boards (caps check out OK)
VIT70023.80 REV:5
https://www.shopjimmy.com/philips-99...verter-kit/

[nomoresonys]

There may be a/some more bad cap/s if you only changed the bulging ones.

[bcstedt]

I've been ESR testing all the caps I've come across and all the PS caps that look ok test ok.

There's a bunch of SMD Samyoung caps (and some others) on the main board that don't test out too well but don't really seem bad. I've replaced a couple (out of 80) but no change yet.

I've disconnected the T-Con board but that doesn't have any affect.

The service doc's I've found so far haven't been to helpful but I'll keep digging.

[bcstedt]

I've noticed a slight bow on the main board at the processor chip which gets pretty hot to touch. I'm leaning towards a issue with the BGA chip so I'll try preheating it to see if that has an effect.

I checked the CPU heat-sink and it does warm up even if the back-light and image is off. It does seem that something needs to "warm up" before it will successfully restart. Still looking ...

======
Update: I preheated the cpu area to 55*C using a hairdryer on low. TV turned on successful three times out of three with 10min intervals. Looks like I might need to bake/solder the BGA on the cpu.

Update 2: Letting the mainboard / cpu cool down and testing in 10min intervals.
- 30*C failed to start
- 28*C failed to start
- 26*C failed to start

[bcstedt]

Based on the info above I'd like to try reflowing the BGA of the mainboard cpu area.

Best/safest method to try? With/without liquid (thinned out) flux?

[diif]

What hot air tools do you have ? Yes use flux, there shouldn't be any need to thin it out, the heat should do that.

[bcstedt]

Not much right now. I've got a semi-regulated heat-gun somewhere and a cheap hot-air station (lost in moving). I was curious about using a heat-lamp? I saw a YT repair doing that with a BGA.

[diif]

The heatsource is not to important. Ideally you want to heat the whole board to around 100c and then just add extra heat from the top to reflow the BGA.
Use flux and get one of these https://www.ebay.co.uk/itm/404702083942 , place the probe next to the processor and ensure you reach at least 218c.

[bcstedt]

Thanks. I have a few K type probes for my multi-meters that I can use. Will give it a try and report back.