Lenovo THINKPAD S2 is just difficult to maintain due to protection and isolation

Machine model: Lenovo THINKPAD S2

Main board number: DA0PS8MB8G0

Fault phenomenon: 0.0012A plug-in, actually measured as no protection and isolation, no common point.

Maintenance process:

The old driver of this machine knows that there are many problems with ISL9237 in general. After disassembling and measuring VDD, VDDP 5V and DCIN 20V, the data is normal, and ACIN is about 4.3V, which is abnormal.

Lenovo THINKPAD S2 is just difficult to protect and isolate. Figure 1

When PR3111 and PR11622 are removed, the measured PR11622 of 100K becomes about 120K. The material plate is removed and replaced with a resistor, and the plug-in is still similar. At this time, I measured 14 and 15 times and found that the current detection resistor was not broken, so I found a 9237 in the spare parts box and changed it.

After the replacement, I found that it was still the original fault, and I struggled for a long time. I found that the VDDP of this chip was only about 4.3V, and I greeted the chip for a long time. The next day, a SF arrived early in the morning, and the replacement was exactly the same as the original chip failure.

Next, step by step, measure all the conditions again, and change all the MOS of PWM, which is still the same. After cooling down, I observed that there seemed to be a standby at the moment of plug-in. Is it that the protection is out of power?

Please take out the oscilloscope immediately and find out that the connection end of PL2006 and PQ2071, that is, when the power supply is used, this end has a waveform at the front end and a waveform at the back end.

Lenovo THINKPAD S2, however, is difficult to protect and isolate. Figure 2

This circuit is no different from our usual PWM circuit, except that there is an additional battery discharge direction.

It can be seen that the PWM buck circuit composed of PQ2071, PQ2070 and PL2006 should flow from the S-class of PQ2073 to the common point of VIN, but it is definitely abnormal that there are waveforms before and after here.

Lenovo THINKPAD S2, however, is difficult to protect and isolate. Figure 3

After thinking hard, I really couldn’t find the direction. I could only wonder if the charging chip received the wrong signal, so I turned on the MOS tube for charging and discharging at the same time. So I disconnected the SMBDATO data cable and plugged it in again, and sure enough, the common point was successfully generated.

Lenovo THINKPAD S2, however, is difficult to protect and isolate. Figure 4

A new problem has arisen. Under what circumstances did EC send the wrong signal? Is EC broken? With the mentality of solving, the measured diode value is normal, and the problem lies in the pull-up voltage. You can see that the voltage is about 4.1V, and you can finally see a little hope with an ecstasy in your heart.

Lenovo THINKPAD S2, however, is difficult to protect and isolate. Figure 5

Find the source directly. The 3V LDO is also 4.1V Disconnect the rear stage.

Lenovo THINKPAD S2, however, is difficult to protect and isolate. Figure 6

It turned out to be a string of electricity. Turn off the 5V voltage and return to normal.

Lenovo THINKPAD S2, however, is difficult to protect and isolate. Figure 7

After that, it was demolished crazily.

It was caused by the seat. This seat has been encountered twice, but it was removed after a bad B chip was replaced, and it was found that it had nothing to do with it and was put back. It can only be said that the bad chip was harmful. At this point, the maintenance is over!