Lenovo Ideapad 1501B_01_01 dead motherboard

[Charles24]

The motherboard turned on for 3 sec and automatically turned off. All inductor voltages are present in the ram module 1.35v, CPU core, 1.8v, 1.05v, 3.3v, and 5v stand-by. Ampere reading in the DC power supply when i turn on the board is 1st 16mA then to 110mA and then to 250mA, when the board is turned off it goes to 4mA all this happened in 3 sec. When the board is turned off only LDO is present at 4mA.

I plugged out the DC-regulated power supply and did some off-state checking to see any shorts in load switches and then primary and secondary power line regulators and MOSFETs.

After a while, I plugged in the DC power supply, and Suddenly ampere went to 300mA and settled at 110mA, the thing is, at this time no voltages were present except 5v and 3.3v standby, and 1.8v and 1.05v. Now the ram inductor shows 2.2ohms which shows the symptom as short. while the ampere reading is at 110mA in the standby state, no any voltages except LDO but the sandy IC TPS1285B is getting abnormal heat.

May I know what could have happened to the board while troubleshooting? I couldn't figure out

Thanks

[mcplslg123]

Re: Lenovo Ideapad 1501B_01_01 dead motherboard

Very likely you accidentally touched 2pins while measuring. Measure resistance to GND on LDO pin of TPS51285B(no power attached). However, going by your reading,SOC is damaged.

[Charles24]

Re: Lenovo Ideapad 1501B_01_01 dead motherboard

Very likely you accidentally touched 2pins while measuring. Measure resistance to GND on LDO pin of TPS51285B(no power attached). However, going by your reading,SOC is damaged.

Thanks for your advice, Yes it was SoC damaged.

[mcplslg123]

Another sad ending......

[Charles24]

Another sad ending......

Yes, it's really hard to say😢. It's like killing a patient whom came with fever. Recently, I destroyed another board😭. Actually I found the problem and turned on the board. It came with no power and I found problem with RTC section. As RTCRST# was reading 24ohms on SOC side. 20kohms resistor is used to pullup 3.3v to RTCRST#. As we know until RTCRST# is low, Power management of SoC is not going to wake-up. And as it was reading 24ohm, 3.3v on the other side of resister didn't pass to RTCRST# just I saw 0.012v. I thought, at this point 50% of SoC is damaged through RTC section reading 24ohm at RTCRST#. I tried alternative way to make high the RTCRST# by injecting 3v with low amps from regulated power supply. I used a jumper wire to RTCRST# and connected to regulated power supply. Now I used adapter for power and regulated power supply for pullup voltage of RTCRST#. Pressed power button fans spinned, I was surprised with the board's reaction. I touched SOC it gradually started heating up and I thought it came to live again. I immediately powered off and tried to connect a pendrive with LED indicator to see whether it reads to make sure display is executed. At this point I have to just disconnect regulated power supply from RTCRST#, however, I didn't disconnect adapter power and the board was live. As the jumper wire connected to RTCRST# was little long and flexible it became flat lying on the board and accidently touched main power source 19v going to a section and shorted RTC section. Immediately I plugged out the charger and saw reading on RTCRST# I got 1.2ohms. I became fairly certain, Oh I destroyed it😫. Then I plugged in charger, 3v_alw and 5w_alw regulators were getting heat. As these 3v and 5v goes to power management of SOC. I thought ok, now I can't do anything at all just wasted my time and destroyed a board with carelessness. I was really upset and so worried about this. I actually, be very careful with motherboard and handle with care. Unfortunately nothing helped.