How to troubleshoot i2c that's held low?

[caphair]

I'm trying to fix an iPhone that won't boot up.

This model has two i2c lines (SDA and SCK) the clock line is at a steady 1.8vbut the data line is stuck low at 200mv where normally it's also at 1.8v

There are multiple chips sharing the same i2c lines including the processor.

In the past I was able to fix a similar problem by removing each ic sharing the i2c lines one by one until the data line went high again. However it's very time consuming.

Is there a way to pinpoint the troubled ic without removal of each one by one?

[stj]

Re: How to troubleshoot i2c that's held low?

tie the line to the 1.8v supply and see if anything heats up.
*but* because the circuits are cmos, it could be running in reverse.
that is, using a pulldown resistor with the chips taking the line high.
so you may also find it's an open-circuit in a chip rather than a short.

if you have the schematics, does it have pullup/down resistors?

[caphair]

Re: How to troubleshoot i2c that's held low?

Yes it uses a pull-up resistor already measured it and it's not open.

At 1.8v applied to that line it wouldn't draw much current to see what's keeping it low by heat I imagine?