GL702VM not charging/unable to power on

[Peter Toropov]

Removed PQ8901, resistances I got on PU8900 IC:

ACN:...................................0 Ohm (short)
ACP:...................................0 Ohm (short)
CMSRC:.............................4.55mO
ACDRV:..............................7.35mO
ACOK:................................1.1mO
ACDET:..............................4.25kO
IADP:.................................197.5kO
BATPRES:.........................99.3kO
TB_STAT:...........................19.85kO
BATSRC:............................8 Ohm
BATDRV:............................3.9mO
SRN:..................................9Ohm
SRP:..................................9Ohm
ILIM:...................................71.7kO
IDCHG:..............................183.2kO
IMVP8_PSYS_INFO:.........28.6kO
PROCHOT:........................3.5mO
SDA:..................................0.64mO
SCL:...................................0.66mO
CMPIN:..............................58.5kO
CMPOUT:..........................45kO
GND: GND
LG:....................................4 Ohm
REGN:..............................3.08mO
BST:..................................2.95mO
HG:...................................0 Ohm (short)
LX:....................................0 Ohm (short)
VCC:.................................4.15kO

[mon2]

Based on the very low resistance to ground measurements of SRN / SRP, the charger IC appears to be defective. Suggest to flux it well and remove off the board. Do not replace this part yet. Then still with no power, measure the resistance to ground of each pin on the charger IC. Need to know if the SRN / SRP and other pads are restored to normal values. What is the value of the ACN / ACP pin to ground after the charger IC is removed?

Be patient so that the charger IC pcb pads are not torn off the board. Use tweezers to slightly nudge the IC to see if the part can be removed.

[Peter Toropov]

Both the ACN and ACP are shorted to ground.

ACN: short
ACP: short
LG: short
SRN: short
SRP: short
HG: short
LX: short

[mon2]

Would you have resistance values on these points or using diode mode checking? Best to use the lowest resistance scale on your meter and then measure again to ground.

Interested in the resistance readings in ohms for each.

[Peter Toropov]

They all give 0 Ohms in resistance mode.

Will check in diode mode later as the multimeter I have right now can't measure diode mode.

[mon2]

Diode mode is not required if the resistance scale is known to be stable. Short your probes and you should also see a 0 ohm resistance. Concern is with the 0 ohms to ground on the main power rail. Inspect the board for obvious solder shorts on the board. If not present, then inspect the resistance across the mosfets (source & drain; source & gate; gate & drain pins); check the resistance to ground of each inductor on the board.

Do you have an adjustable power supply for voltage injection? Do not proceed yet but perform the above reviews.

[mcplslg123]

Schematic/bdv is not linked-so cant check but its clear that the damage is very likely in high side charging mosfet. Remove the mosfet connected to HG pin of charging ic and check again for short.

[Peter Toropov]

I apologize for not replying earlier, I, sadly, don't have a variable power supply for voltage injection. Checked all the inductors, almost all of them gave a resistance of 0 ohms to ground. Should I make a list of one's that have resistance? Or both with resistance and no resistance?


Also, removed the mosfet connected to HG, PQH8901. Short to ground on IC HG pin, as well as on AC_BAT_SYS has disappeared. Resistance on AC_BAT is now 3.9mO. Checked the battery connector itself, BAT_CON to ground gives 0 Ohm resistance.

I have also received some replacement charger IC's

Can I attach the boardview in the next post?

[mon2]

Post a pic of the front face of your meter while measuring one of the 0 ohms to ground. Something else may be wrong if you are reading 0 ohms on so many coils.

[Peter Toropov]

Apologies for not replying for so long, had to catch up with school.

Checked HG again, just in case, got no reading from it to GND.

Attaching the pictures of resistances from inductors to ground and a boardview.

[Sephir0th]

CPU Core supply measuring 0 Ohms usually means a dead CPU, except there "just" went something very wrong with your capacitor replacement. But it stongly looks like a typical high-side short.
Charging rail measuring 0 Ohms explains the not charging battery. However, from my understanding there is no point to proceed with the repair attempt. Even of you fix the problem in the charging circuit, you can't do anything for the CPU anymore.

[Peter Toropov]

That's unfortunate to hear, but at the same time was kind of expected. Nevertheless, due to this "project" being an educational one to me in terms of how to troubleshoot things, practicing soldering and general knowledge gaining, I would like to try and resolve those high and battery rail shorts, if it is possible.