Dell 5420 / 7420 series laptops can’t be powered on for common repaired

Dell 5420 / 7420 series laptops can’t be powered on for common repaired

Machine model: DELL 5420/7420 series

Malfunction: Notebook Won’t Turn On

Maintenance process: the version numbers of DELL 5420 and 7420 are DA0R08MB6E4 and DA0R08MB6E2, and the drawings are common, and common failing should be known to everyone. 

Current 0.9 or so does not run code, brush BIOS directly, memory VCC up and down tubes love to burn, solution: Change the Capacitor chips together, change the south bridge directly when the USB in the system is not working, and remember to brush BIOS after the change, otherwise it will not light up. 

Dell 5420 / 7420 series laptops can’t be powered on for common repaired Figure 1. 

Today, we want to talk about another common failing. The bare board power-on current is 0.35 or so, which is the same as replacing the CPU. According to experience, this is definitely not CPU VCC. As soon as other VCC is normal, there will be no CPU VCC and Jixian VCC. Open the drawing as follows: 

Dell 5420 / 7420 series laptops can’t be powered on for common repaired Figure 2. 

Measure the fourth pin IMVP_VR_ON 0V directly, that’s the problem. IMVP_VR_ON is sent by EC. When EC closes HWPG, it sends IMVP_VR_ON to turn on CPU VCC and find HWPG. 

Dell 5420 / 7420 series laptops can’t be powered on for common repaired Figure 3. 

According to the measurement, HWPG is normal at 3.3V, which is either EC bad or BIOS. Directly under a BIOS brush in the forum, the problem remains the same, and it remains the same after looking for the same EC. 

Check all major VCC, South Bridge VCC and EC VCC from the beginning, but no problem is found. After testing 109 pin, it was disconnected. H_CPUDET# is the CPU detection signal. EC didn’t detect CPU, so it didn’t send VCC. It’s not even possible to force CPU VCC to be turned on in the middle. Basically, it can be concluded that this is VCC. After reading a lot on the forum, this problem has not been solved.common failing is a broken line under BIOS, as shown in the picture below. 

Dell 5420 / 7420 series laptops can’t be powered on for common repaired Figure 4. 

Dell 5420 / 7420 series laptops can’t be powered on for common repaired Figure 5. 

Dell 5420 / 7420 series laptops can’t be powered on for common repaired Figure 6. 

Dell 5420 / 7420 series laptops can’t be powered on for common repaired Figure 7. 

Dell 5420 / 7420 series laptops can’t be powered on for common repaired Figure 8.