RAM Section advanced Circuit trace no voltage in RAM. DA0X8TMB8E1 REV: E
I received an HP ProBook 440 G10 laptop that was sent in for repair. The customer reported that the power indicator light would turn on, but the laptop itself would not start. They attempted to reprogram the main BIOS in an effort to fix the issue, but the problem continued, so the device was forwarded to me for further inspection. Figure 1 shows the front view and a cross‑section of the laptop, which helps illustrate the condition of the unit when it arrived.
Figure 1 HP PROBOOK 440 G10 Motherboard – Front view and section overview.
In the first step of my diagnosis, I powered on the laptop using a bench power supply. The meter showed a current draw of around 140 mA, but the laptop still did not turn on. I then opened the laptop and checked all the main voltage lines. Most of the power rails were normal, but the RAM voltage was only 0.48 V instead of the required 1.2 V.
After further inspection, I found that the MOSFET in the RAM power section was not receiving the correct enable voltage. This issue is shown in Figure 2.
Figure 2 RAM Power supply circuit
After tracing the circuit, I found that the RAM power MOSFET was not receiving its enable signal because the RAM IC located directly behind it was faulty. The enable voltage was supposed to come from this IC, but it was not outputting the signal. I replaced the IC, and after the replacement, the laptop powered on normally without any further issues.
Figure 3 RAM IC to MOSFET track on the backside
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Amazing circuit reverse tracing