Toshiba M115 Irregular Power Off

 One exception of TOSHIBA M115 power-on and power-off maintenance

A piece of difficult fault board was sent by a colleague in the same place for repair. The description of the fault is that the power-on is normal, but after a short period of time, it will power-off and go to standby state, which can be triggered repeatedly. 

No matter what working state the machine is in, it will be powered off. According to the phenomenon that it can be triggered again after power failure , it can basically be ruled out that the protection action of the temperature protection circuit (because according to the circuit design of this machine, if the temperature protection is effective, then the turn-on signal of the standby voltage will also be pulled down. The machine will definitely not be able to trigger).

Then contact the customer for the maintenance process before sending it for repair. It has been judged that the cause of the power failure is that the RSMRST# of the south bridge is pulled low, which leads to the low SLP_S5# and SLP_S3# of the machine, and directly enters the S5 state. Because the RSMRST# signal is sent to the south bridge by the EC chip, and the EC has no related control signal. 

After searching for a long time, no direct control signal was found, so the The biggest possibility is that the abnormal operation of the EC causes RSMRST# to be It is very simple to judge whether this situation is the cause of power failure, directly cancel the control of RSMRST# by EC, and use another signal as the reset signal for the south bridge to return to the suspend circuit.

Just do it when you think of it, so first disconnect the line from EC to South Bridge, and then directly connect the signal to the voltage of +3VAL through a 1K resistor at the south bridge end, and then power on again, the machine is automatically triggered, this is As expected, then keep the machine turned on for one minute, two minutes. . All the way to five. It didn't lose power for a few minutes. It seems that the power failure was caused by EC pulling down RSMRST#. 

At this time, although the machine can work normally, the customer must not accept it, because as soon as the adapter is plugged in, the machine will automatically trigger the boot, so there is no other way.

Find the root of the problem, and things will be easy to handle. Just find a signal with a timing similar to the RSMRST# signal to replace it, but after careful consideration, this is not the case, because the SUS power supply of this machine is sent when it is in standby.

However, RSMRST# is sent out after triggering, and there is no other signal similar to RSMRST# in timing, so it is only necessary to build another circuit to provide RSMRST# in accordance with the timing , referring to the design of ASUS Idea, draw a sketch, and then construct according to the drawing. One hour later, the circuit structure is completed, the machine is powered on, the machine is in normal standby, triggered, and then powered on , everything is running normally. 

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