A1706

[lucasbrand]

Hey folks,

as, even after 24h after my introduction post, I am still not free to create a Thread, I tried to find the most suitable:

I have this dead A1706. Here is what I have checked so far:

• Ampmeter in all 4 USB C Ports: All same, 5.02V, 0.0A, no bootloop
• (Not removing the Power Supply)
• PPBUS_G3H at F7000: 17mV both sides
• PP3V3_G3H at L6900: 0.4mV both sides
• Check for enable at U6903 Pin 10 Test points: 0.31V

I recreated those steps from a video. Now my question: The Voltage for the enable seems pretty low, doesn't it? What's next to check / to suspect to be faulty?

Hope somebody is willing to take me by their hand . Thanks!

[mon2]

• PPBUS_G3H at F7000: 17mV both sides

remove all power. Check the resistance on each side of F7000.

[lucasbrand]

Both sides same behaviour. Started with around 0.7 Ohms counting up continuously.

[lucasbrand]

remove all power. Check the resistance on each side of F7000.

Forgot to quote you

[mon2]

Flux and carefully remove F7000 off the board with hot air. We need to determine which side of the fuse is with the short. Most likely it will be the downstream (consumer) side rather than the upstream (producer / ISL) side.

[lucasbrand]

Ok, thank you! This will take some time as I will have to order tools.

[lucasbrand]

Flux and carefully remove F7000 off the board with hot air. We need to determine which side of the fuse is with the short. Most likely it will be the downstream (consumer) side rather than the upstream (producer / ISL) side.

so what should I do then when the F7000 has been successfully removed?

[lucasbrand]

Flux and carefully remove F7000 off the board with hot air. We need to determine which side of the fuse is with the short. Most likely it will be the downstream (consumer) side rather than the upstream (producer / ISL) side.

And as I struggle to find a beginners guide for desoldering chips, what is a good temp for the hot air station to use? Using severals values (slowly increasing) up to 350°C with some flux on the chip didn't get me to remove it with my tweezers...

[mon2]

Really depends on your hot air tool + air pressure used. Most of these target PCBs are 8L or even more so there are solid copper planes that act like heatsinks. For this reason, an underside pre-heater helps but not always required. Suggest highly to practice on donor boards to learn the process.

Apply lots of flux -> heat at 350-400C for us works well (sometimes need to be higher but watch that you are not burning the board) -> go in tight circles to cover the entire device -> gently nudge (never rush or push too hard) on the device's corner to move when the solder is shiny and melted. Have ventilation to draw the fumes. Watch assorted videos on the same on YT.

[reformatt]

So just to confirm, is 0.7 ohms across the fuse, or a resistance measurement to ground for PPBUS_G3H?

[lucasbrand]

So just to confirm, is 0.7 ohms across the fuse, or a resistance measurement to ground for PPBUS_G3H?

The measurement was to ground

[reformatt]

Ok, so on these boards with a dead short on PPBUS, I go straight to the CPU coils (L7210/L7220, L7270 etc) and check resistance to ground before anything else. If any are 0, then you have a DRMOS short and a dead CPU.