19" TV. Unreadable burnt IC on board MSD309.37A

[edugimeno]

Hi there.
I have this "white label" 19" TV that I bought knowing it was broken. Its like a generic brand like what you would buy a Best Buy.

First thing I realize is that tehe external 12V DC power supply is dead. So having one handy with same voltage, same power, same plug and same polarity, I plugged it in expecting that would be it.

(YES, I DOUBLED CHECKED THE POLARITY, on the sticker and with my multimeter)

So I plugged it in, turn the TV around to realize that the stdby led was on, but at the same time I heard a psssst and smelled the "classic" burnt semiconduct aroma....

Opened it up and close to the PS area, there's a 8 pin IC that I can't tell its markings as it's burned near the id.

I tried to find an schematic for this board with no luck so far.

Any idea, what this IC could be for? Or where to find an schematic? Or why would it make it burn?

See pics. It's U7 on the board, reads something like GR8500 but that seems not to be valid...


Thanks in advance!

[R_J]

Re: 19" TV. Unreadable burnt IC on board MSD309.37A

The number is above the GR8500, clean it with some alcohol and you should be able to read it, I can almost make it out, xxxx57x
What's the number on U3 next to it
Make & Model might be helpful as well

[dick_barton]

Re: 19" TV. Unreadable burnt IC on board MSD309.37A

Looks like there's also a capacitor missing from pin8

[edugimeno]

Re: 19" TV. Unreadable burnt IC on board MSD309.37A

The number is above the GR8500, clean it with some alcohol and you should be able to read it, I can almost make it out, xxxx57x
What's the number on U3 next to it
Make & Model might be helpful as well

I'll give it a try, hard to focus on such a surface

[edugimeno]

Re: 19" TV. Unreadable burnt IC on board MSD309.37A

Looks like there's also a capacitor missing from pin8

I saw that too, but I can't find any loose part in the case, when we find the part number for the IC U7, its datasheet will probably tell if that capacitor is mandatory

Thanks

[R_J]

Re: 19" TV. Unreadable burnt IC on board MSD309.37A

What's the number on U3 next to U7?

[edugimeno]

Re: 19" TV. Unreadable burnt IC on board MSD309.37A

Ok, the other IC U3 is AIC2565 (23V 3A Step-Down DC/DC Converter)
Now I applied some alcohol to the burned IC (U7) and I can read it:
U7: AIC2857F: 2A 23V Synchronous Step-Down Converter.
So both are step down converters. I guess U7 had some issue with whatever it is feeding
The missing capacitor below it is at Pin 8: "SS: Soft Star Control Input. SS controls the soft star period. Connect a capacitor from SS to GND to set the soft-star period. A .1uF
capacitor sets the soft-star period to 15ms. "

Should I replace the IC and add the capacitor? Or should I expect something else to be provoking the shortcircuit at the output?

Thanks

[dick_barton]

Re: 19" TV. Unreadable burnt IC on board MSD309.37A

It looks like pin 3 is the output so check the resistance from pin 3 to pin 4.

[edugimeno]

Re: 19" TV. Unreadable burnt IC on board MSD309.37A

Well right now resistance between 3&4 is ~0 but I still need to remove the IC to rule out the IC being the shortcircuit itself