Sudden power failure of HP TPN-Q191 notebook during normal use

When the TPN-Q191 notebook is in normal use, it suddenly loses power. Carefully observe the fault phenomenon. After running for 3 days, the power indicator goes out. When it is turned on again, the self-test page reports CMOS error 502. According to the drawings, it can be seen that PQ1(AP0203GMT-HF) and PQ2(AON7408) are isolation tubes. Because PQ1 has a large current, no replacement is found, only PQ2 is found. After the replacement, everything is normal through plug-in test.

[Machine model] HP TPN-Q191 notebook

[motherboard version number] DAG71MB16D0 REV

[Fault phenomenon] The notebook suddenly loses power during normal use.

Upon receipt of HP TPN-Q191 notebook, the customer described that it would automatically shut down after ten minutes, and then shut down after three or four minutes. The customer had already applied silicone grease, cleaned the dust and reinstalled the system.

[maintenance process]

After getting the machine, after testing, the shutdown mentioned by the customer is actually a power failure. Check the test heat dissipation again. When the power is off, the heat sink is not hot, and confirm that there is no problem with heat dissipation.

Sudden power failure in normal use of HP TPN-Q191 notebook Figure 1

Observe the fault phenomenon carefully. After running for 3 days, the power indicator goes out after power failure, and when the machine is turned on again, the self-test page reports an error CMOS error 502. Because this machine has no CMOS battery, it uses a built-in battery, so after power failure, the error CMOS is reset, and obviously the battery power supply is also disconnected.

Take this phenomenon as a breakthrough, and focus on checking why the battery power supply will also be disconnected. So the AC power supply was disconnected, and the battery was used for 3D test, and five or six round trips were tested, without power failure. Plug in the charger, run for 3D, and it will lose power if you can’t finish it. Take off the battery and run for 3D with the adapter alone, but it will still lose power. Since the single battery is not powered off, the circuit behind the common point is basically normal, and the problem is basically reduced to the isolation circuit.

Sudden power failure in normal use of HP TPN-Q191 notebook Figure 2

Sudden power failure in normal use of HP TPN-Q191 notebook Figure 3

According to the drawings, two pipes PQ1(AP0203GMT-HF) and PQ2(AON7408) are isolation pipes. Due to the high current of PQ1, no replacement was found, but only PQ2 was found. After the replacement, the plug-in test was normal.