Hi,
Try to repair a Thinkpad P72 EP720 NM-B723 MB with I7-8850H processor and N18E-Q1-KB-A1 (P3200) GPU with 6GB memory. Unfortunately there is noinfo what happened to the laptop. I got it disassembled with parts missing, like keyboard, battery.
Unfortunately I have no schematic available for me (requested in the sub porum) but got the boardview file.
Symptom: after connecting to the charger the power led light up for one-two second and switch off. After a couple secons the power led light up for half a second and switch off. No battery, no IO board, no memory, no keyboard connected to the MB.
Checked the resistance on the power rails. Measured VCCPUCore resistance to ground 2 ohm, VCCGFXCORE_D 0.1 ohm. I have no experience on these resistances but I thought the GFXCORE rail is shorted.
Thermo camera was not able to pinpoint any parts with increased heat. The only visible change was the small heatup of the VCCPUCORE inductors and drivers.
Checked the NCP81274 phase buck controller controlling the VCCGFXCORE drivers with scope. PWMs are present, VCCGFXCORE goes to 1.25V and dorps to zero withing half a second. Power good PGOOD signal goes up and down accordingly. On the other hand according to the boarview file the PGOOD signal pulled up but not routed anywhere else.
Checked the NCP81215 three output controller controlling VCCPUCORE with scope. PWMs are present VCCPUCORE goes about to 1.3V and drops zero within a second.
Injected 0.9V (5A limit) on VCCGFXCORE. I got no voltage drop and 2 amper but there was not any heat up parts on the thermo camera. The GPU slowly warmed up to 32Celsius. I do not really understand this short. If it would be short the current should have reached the limit but not.
Same injection to the VCCPUCORE rail. No voltage drop, 1A current, no heated parts.
Removed the four coils, big tantal caps from the VCCGFXCORE rail measured 0.4 ohm resistance to ground, increased from 0.1ohm, it is quite a lot. Measured the lo and the high side resistance to ground of the drivers, seems to be OK, in couple Kohm range.
At this point I am asking help how to proceed forward. Do the GPU or the CPU toasted? Injection is not supporting this theory. These amperes are within the limits, there are no under and over voltage situations therefore the controllers should operate continously.
Unfortunately I do not know the power sequence of this laptop. As far as I see the power management is controlled by one of the two Lenovo ThinkEngine chip, but there is no documentation on the net about this. It could be possible there is an another reason the rails are disabled within a short period of time.
If anybody knows these power controller ICs thsn please advise how to measure the possible reasons of the rail disabling.
Any advice is appreciated in advance.
Try to repair a Thinkpad P72 EP720 NM-B723 MB with I7-8850H processor and N18E-Q1-KB-A1 (P3200) GPU with 6GB memory. Unfortunately there is noinfo what happened to the laptop. I got it disassembled with parts missing, like keyboard, battery.
Unfortunately I have no schematic available for me (requested in the sub porum) but got the boardview file.
Symptom: after connecting to the charger the power led light up for one-two second and switch off. After a couple secons the power led light up for half a second and switch off. No battery, no IO board, no memory, no keyboard connected to the MB.
Checked the resistance on the power rails. Measured VCCPUCore resistance to ground 2 ohm, VCCGFXCORE_D 0.1 ohm. I have no experience on these resistances but I thought the GFXCORE rail is shorted.
Thermo camera was not able to pinpoint any parts with increased heat. The only visible change was the small heatup of the VCCPUCORE inductors and drivers.
Checked the NCP81274 phase buck controller controlling the VCCGFXCORE drivers with scope. PWMs are present, VCCGFXCORE goes to 1.25V and dorps to zero withing half a second. Power good PGOOD signal goes up and down accordingly. On the other hand according to the boarview file the PGOOD signal pulled up but not routed anywhere else.
Checked the NCP81215 three output controller controlling VCCPUCORE with scope. PWMs are present VCCPUCORE goes about to 1.3V and drops zero within a second.
Injected 0.9V (5A limit) on VCCGFXCORE. I got no voltage drop and 2 amper but there was not any heat up parts on the thermo camera. The GPU slowly warmed up to 32Celsius. I do not really understand this short. If it would be short the current should have reached the limit but not.
Same injection to the VCCPUCORE rail. No voltage drop, 1A current, no heated parts.
Removed the four coils, big tantal caps from the VCCGFXCORE rail measured 0.4 ohm resistance to ground, increased from 0.1ohm, it is quite a lot. Measured the lo and the high side resistance to ground of the drivers, seems to be OK, in couple Kohm range.
At this point I am asking help how to proceed forward. Do the GPU or the CPU toasted? Injection is not supporting this theory. These amperes are within the limits, there are no under and over voltage situations therefore the controllers should operate continously.
Unfortunately I do not know the power sequence of this laptop. As far as I see the power management is controlled by one of the two Lenovo ThinkEngine chip, but there is no documentation on the net about this. It could be possible there is an another reason the rails are disabled within a short period of time.
If anybody knows these power controller ICs thsn please advise how to measure the possible reasons of the rail disabling.
Any advice is appreciated in advance.
But today, I’m making an exception here. Why? No idea. Perhaps only because the repair details are still “fresh” in my head… which is ironic, given this is a 16 year old monitor that hardly anyone will care about today. It is new to me, though. 
I picked it up last November from someone on my local Craigslist. It wasn’t very close to where I live, but was close to a family friend that I had to go visit anyways. So after watching the posting on Craigslist for a few weeks and seeing it getting...
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