I2C data lines short

[greencardigan]

Hi,

I've just finished building a batch of 6 boards and one has a issue with the I2C lines.  There seems to be a short between the data lines and ground.  The resistance between either data line and ground is 0.3 ohms.  Resistance across my 4.7K data line pull up resistors is 2.36K (i.e. they're in parallel).

I can't see any issue with the board or soldering, so I'm assuming there is an issue with one of the three ICs connected to the I2C bus.

Is it possible to identify which IC is causing the short before removing them?

Schematic pdf for the board is here. https://github.com/greencardigan/TC4-shield/blob/master/hardware/TC4/TC4%20V600/tc4-controller-0600-sch.pdf

Edit: I've already tried reflowing the pins on the three ICs.

[Ian.M]

Two of the chips are SOICs, so you can easily lift individual pins.   Remove as much solder as possible with desolder braid then lift the pin with a mounted needle while heating it.   I always like to slip a sliver of Kapton sheet or waxed paper under the pin to confirm there aren't any solder whiskers maintaining contact so I don't have to lift the pin high enough for visual inspection of the gap.   

Don't forget to bend the pin back down before resoldering it after you are done testing.

[greencardigan]

Thanks. I lifted the data pins on both SOICs without any luck. Then removed the smaller IC, I2C headers and pull up resistors. Still no luck.

Finally removed the two SOICs completely and found something underneath the EEPROM. It was easily scratched away with tweezers but was probably just a solder bridge up under the chip.

Resoldered all the parts and it's back in action. Only needed to replace the MCP9800.