820-2850-A Won't start

[CRC2018]

Got an 820-2850-A board in last week which the customer told me was intermittently not charging. Was no green light on it at all. Found a problem with the ISL6259 (DCIN Pin3 was 3ohm short to ground when ISL6259 was on board) which i've replaced and now getting the green light but it still wont start. PPBUS_G3H is pulsing between 13.3v and 2.5V.

Cannot see any shorts on PPBUS_G3H and have replaced the ISL6259 again now but still the same behaviour.

Has anyone seen this before and knows which component is the likely culprit?

DC_IN voltage is 16.5V as I would expect now (it was 1V before changing the ISL originally)

 

[TCRScircuit]

PPBUS_G3H is pulsing between 13.3v and 2.5V.

This is typical of a current sensing issue. Resistance between pins 17/18 and 27/28 of the ISL6259? Measure between the pins, not to ground.

 

[2informaticos]

Did you try SMC bypass?
Check exact resistance between pins 17/18 and 27/28.
Remove F7040 and check if get steady C7040 voltage.

 

[CRC2018]

Pins 17/18 - 3ohms
Pins 27/28 - 20ohms
Both measured at the ISL

 

[CRC2018]

Right i've replaced the ISL again with another new chip and it's now making PPBUS and starts! The machine does however have another issue - when I disconnect the charger and reconnect it then the light comes orange on the charger but it doesn't start to charge the battery. If I SMC reset the system then it will start charging the battery again until I reconnect the charger.

 

[2informaticos]

R7000 is good?

 

[CRC2018]

Checked and R7000 is good.

 

[2informaticos]

Check what happens when BIL is disconnected (J6955).