Hitachi LED TV le24ecd05au turns on sometimes

[hernan_perez_br]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Hi Tom, here are more readings.
I noticed that there is one chip named aic2857F that receives 0.63v and I think it should receive 5v.
This is the schematic (which I do not fully understand)
http://www.analog.com.tw/ImgShow/1.gif
In the image below I put all the measurements in the pins.
Thanks!

[tom66]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Looks like there is a 5V standby and a 5V main. The 5V standby is OK, but the 5V run is bad. I know we've had AIC2857 go bad before so it wouldn't surprise me. However, I do notice that pin 7, enable, is LOW. So the chip should not be working. i.e. it is correctly operating.

Does it go HIGH when the TV works?

It is possible the IC has an internal short. To rule that out you can try desoldering it off the board then checking pin 7 again, but on the exposed pad instead of the IC.

Info on theory of operation of buck DC-DC converter, like this chip:
http://en.wikipedia.org/wiki/Buck_converter

[hernan_perez_br]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Hi Tom, can also this black cylinder (I think this is a coil) be faulty ? (see photo) it provides 0.63v to the AIC2857 chip instead of 5v.
Also given that I have 5v in the mainboard, can I bridge the 5v standby with the 5v main?
Thx

[hernan_perez_br]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Hi Tom, finally I "desoldered" the aic2857 and due to my lack of desoldering knowledge, I ruined the pads and some small resistors. So the mainboard its gone.
It is still powering, the standby and power led works. My last option was to bridge the 5v (pin 3) to the 5v stand by but still the tv does not turn on.
So I suspect the mainboard is gone and I should throw it away.
Thanks