A1708 820-00840 no power

[mon2]

Re: A1708 820-00840 no power

My bad...thank you for the correction. Too many netnames in my fading head.

Remove all power. Measure the resistance to ground @ F7000 (pad # 1).

This should be with F7000 fuse removed.

Next, measure the VOLTAGE to ground for:

SMB_SMC_CHGR_SDA
SMB_SMC_CHGR_SCL

the above SMBUS (I2C) lines are used to communicate with the ISL9239 @ U7000 to allow for this IC to become either a BOOST or BUCK regulator.

Since you have 20V as input, this regulator should enter BUCK mode (high input voltage; low output voltage).

[nassih]

Re: A1708 820-00840 no power

what's creating PPBUS_G3H in this model?

[mon2]

Re: A1708 820-00840 no power

U7000 is the switching regulator.

It must be working but so should the external mosfets @ Q7030 & Q7040.

The SMB_SMC communication lines must be working to allow for the configuration of U7000 to act like a BOOST or BUCK regulator.

Do you see any damage to U7000 ? Inspect with your microscope to see if it looks ok.

[nassih]

Re: A1708 820-00840 no power

no damage on U7000,i have replaced U7000,Q7030,Q7040,U6990,D6905 no issue

[mon2]

Re: A1708 820-00840 no power

With power adapter connected, measure the voltage to ground of:

SMB_SMC_CHGR_SDA
SMB_SMC_CHGR_SCL

Meter in DC volts (20v or higher is ok) mode.

Red meter probe to one of the above points. Black meter probe to ground (shield is ok).

Post each measurement.

U7000 (ISL) controller is configured over the SMBUS. Checking if they are stuck.

[nassih]

Re: A1708 820-00840 no power

SMB_PMIC_SDA : 3.2 v
SMB_PMIC_SCL : 3.2v
but the two voltages are not stable,fluctuation between 2.2v and 3.2v

[mon2]

Re: A1708 820-00840 no power

The fluctuations are ok. This confirms that the measure line is switching between high / low logic levels. The switching is not being properly measured by the meter since it is not fast enough. This is common to most meters.

To properly view the toggling of the SMBUS signals, you will need an oscilloscope or logic analyzer (some cheap ones are available on Aliexpress).

With a logic analyzer and SMBUS plug-in, you can decipher what the SMBUS master is communicating with the SMBUS slaves (ISL, etc.).

For the missing PPBUS_G3H voltage,

1) is F7000 in or out of the PCB ?

2) remove all power -> meter in resistance mode -> measure the resistance to ground of F7000, pin # 1 (aka ISL - U7000 side).

What is the resistance reading ?

3) What is the resistance between the F7000 fuse PCB pads (if the fuse is installed) ? It should be ~0 ohms if the fuse is NOT blown.

[nassih]

Re: A1708 820-00840 no power

thank you mon2 for your support and effort to help people here it's interesting and useful, ok I'm going to take these tests and measurements tonight, thanks again

[nassih]

Re: A1708 820-00840 no power

i have measured with the oscilloscope SMB_PMIC_SDA and SMB_PMIC_SCL , I can see signals but I don't know the normal state (I'm not familiar with the oscilloscope),
F7000 have 560k resistance to ground and 0.1ohm (F7000 in)

[mon2]

Re: A1708 820-00840 no power

Can you clarify the 0.1ohms? How was this measured?

Meter probes across the fuse?

[nassih]

Re: A1708 820-00840 no power

Can you clarify the 0.1ohms? How was this measured?

Meter probes across the fuse?

yes sir
i think i have a bad Q7040,Q7030 they are recovered from an donor board, I'm going to order them right away, maybe that's the origin of this problem.

[nassih]

Re: A1708 820-00840 no power

yes indeed I removed q7030 there is a short between pin1,2,3,13 and pin5,6,7,8,9,10,11,14

[nassih]

Re: A1708 820-00840 no power

sorry it was a bad measurement, the mosfet was closed,