Pro Slim Plus QBS1250, no power, power rail failure

<The Pro Slim Plus QBS1250 is a Desktop computer. Moving your post out of Laptops --> Inspiron board and into Desktops --> Dell Pro Desktops. DELL-Admin>

Subject: Technical Support Request: Dell Pro Slim Plus QBS1250 - No Power / Power Rail Failure

Good day,

I hope this email finds you well. I am reaching out to request technical assistance for a Dell Pro Slim Plus QBS1250 desktop that fails to power on.

We have performed a systematic troubleshooting sequence to isolate the fault, but the issue persists. Please see the details of our diagnosis below:

Troubleshooting Steps Taken:

• Step 1: Power Interface & Cables: Conducted a visual inspection of the power button and verified all internal cable seating. We swapped the power cable with a known-good cable; no change in status.

• Step 2: Power Source: Tested the unit on multiple independent wall outlets and bypassed all surge protectors to rule out external power delivery issues.

• Step 3: Component Isolation (Barebone Test): Disconnected all non-essential components, including SSDs/HDDs, Wi-Fi cards, and the CMOS battery. We attempted to boot with only the PSU, motherboard, and RAM.

• Step 4: RAM & POST Diagnosis: We attempted to boot without RAM to trigger a diagnostic beep/LED code, but the system failed to produce a POST code. When RAM is installed, the system remains unresponsive.

• Step 5: RTC Reset: Performed a Real-Time Clock (RTC) reset to restore BIOS factory defaults.

• Step 6: CPU Inspection: Reseated the CPU and inspected the socket for bent pins; no physical damage was found.
• Step 7: Checked and confirmed that the power button and cabling are fully functional and not the cause of the failure.

• Step 8: PSU Voltage Verification: The Power Supply Unit was tested both under load and independently. We confirmed the following DC voltage outputs:

  • Output Rails: +12VA1, +12VA2

  • Standby Rail: +12VB

Current Status:

Despite these efforts, the unit remains unresponsive. Please note that we do not have a spare known-good PSU or motherboard compatible with this specific model to perform a swap test.

Given that we have ruled out basic connectivity and peripheral interference, we suspect a deeper hardware fault on the motherboard or PSU. Could you please advise on the next steps for repair or provide a deeper diagnosis?

Thank you for your attention to this matter. I look forward to your guidance.

Best regards,

Ike Alumani

IT Technician | Global Internet Limited