HP 6550B notebook but Current protection isolated repair

HP 6550B notebook but Current protection isolated repair

Machine model: HP  6550B

Fault phenomenon: the laptop is not isolated by Current protection

HP 6550B notebook but Current protection isolated repair Figure 1.

Maintenance process: at the beginning, there was 0.008 current when the power was plugged in. It felt that the standby was normal, but there was no reaction when Switch was pressed. Since no power on, check the EC working conditions first.

EC VCC, reset and CLK are normal. If you look at the 3v5v side, it is no wonder that no power on will appear.19v VCC, LDO open these are normal, how can there be no VCC?Is Current protection, oscilloscope does not have any action, it seems not Current protection.If you look at the common point 19v Current protection is not isolated, q533 g pole is 19v, this MOSFET is a P channel, of course, it will not conduct.

HP 6550B notebook but Current protection isolated repair Figure 2.

Q533 g-pole controlled q34 dual MOSFET, if you want to q533 conduction, q34 2pin 5pin two control poles must be high level;Measured q342 pin VCC1_POR#_3 is high, 5 pin’adp_EN is low, continue to trace ADP_EN source, ADP_EN is also controlled by EC. How can EC be controlled?

HP 6550B notebook but Current protection isolated repair Figure 3.

Take a look at the charging chip BQ24740 for the moment!The measured acdet of the 5th pin of BQ24740 is 0V, which should be 2.7 or so normally. Trace acdet from two resistor partial voltage of Q19 pole. If acdet in the figure below is high, the G pole of pq19 PNP triode should be low level and controlled by chgctrl_3 and chgctrl_3 is from EC again.

HP 6550B notebook but Current protection isolated repair Figure 4.

We can’t confirm with deact for the time being_EN has no relationship, ancestors for the generation of acdet to see how it will be!short-circuit Q19 acdet produced 2.7V, and EC still did not output ADP_EN high level, it seems that there is no relationship between the two, so when will EC produce ADP_What about en?

I think it is only when EC working conditions are normal that ADP will be sent after receiving a certain signal_EN, then go to EC one by one pin to see which signals are related.

See EC 41 pin AC_ADP_There is no VCC in Pres signal, and it is not sure whether it is high or low at normal time. Trace its source from U6 LM393 first pin.

HP 6550B notebook but Current protection isolated repair Figure 5.

HP 6550B notebook but Current protection isolated repair Figure 6.

After partial pressure calculation, AC_ADP_Pres normal high level, measured as low must be abnormal, output low level must be u63 pin less than 2 pin or U6 itself damaged.

The measured value of 3 pin is 1.8V, and that of 2 pin is 2V. It is strange that there is no output of low level. After partial voltage calculation, the normal value is 2.2 several v. no matter how many other resistors are, quickly find two resistors to replace them. Press Switch directly to get switch, and Current protection isolation is also normal.

HP 6550B notebook but Current protection isolated repair Figure 7.

Conclusion: the process of this machine is to plug in the power, let the EC work normally, and then the EC receives AC_ADP_After pres high level, ADP is sent out_EN controls q34 to generate Current protection isolation. However,Current protection isolation has nothing to do with the charging chip. The chip only controls charging.

Let’s talk about chgctrl_This signal is TR3 Chl_3. The acdet generated by Q18 is only available when the battery is connected, that is, the EC will send out chgctrl after the battery is connected_3. Don’t get tangled.