Member Avatar for dmacdougall

I have a 17" BENQ monitor that is slow to start after being shut off for a couple of hours. The monitor LED blinks but the monitor takes about 5 minutes to light up. However, if the PC is started up after being shutdown for a short period of time the monitor lights up immediately. I think it is due to a weak capacitor? I'd try another monitor, but I have only the one at this site. Any thought?

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  • Latest Post Latest Post by Rik_

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A 17" BENQ that blinks its power LED and only comes on after several minutes when left off for hours points to the backlight/inverter or power-supply electrolytic capacitors as the most likely culprits. was on the right track with the backlight driver, and 's capacitor suspicion fits the thermal behavior described: warm parts (short shutdown) start normally; cold or discharged parts (left off for hours) can fail to produce the startup surge and force repeated restarts (blink).

Why this happens: aging electrolytics lose capacitance and gain ESR, so they either take longer to charge or cannot deliver the initial current. CCFL backlights also require a higher "strike" voltage when cold; an inverter that is weak or in protection will try, fail, retry, and keep the LED blinking until it finally succeeds or times out.

Recommended checks (safe, methodical):

  • Visual inspection (power unplugged): open the rear cover and look for bulged or leaking electrolytic capacitors and dark/brittle solder joints on the main power and inverter boards.
  • Flashlight test: in a dark room with the LED blinking, shine a strong flashlight close to the screen; a faint image means the LCD logic is working and the backlight/inverter is the problem.
  • Multimeter/ESR checks: observe main DC rails during power-up (standby rail vs main rails). Rails that ramp very slowly or never stabilise point to caps or supply faults. An ESR meter or replacing suspicious caps with low-ESR, 105°C rated replacements is a common, cost-effective repair.
  • Replacement options: swap the inverter/backlight board or refurbish the power/inverter board. Inverter boards are often inexpensive; soldering experience is required for board-level fixes.

Safety note: inverter circuits and mains capacitors can hold lethal voltages. Inexperienced disassembly is hazardous; professional repair is the prudent choice if safe bench experience and tools are not available.

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Member Avatar for Rik_

The most common cause of what you describe is a failing backlight driver board. You should be able to get and fit a replacement fairly easily!
Having said that, it's not the only possible cause. If you have and know how to use a digital volt meter then you could do some testing to narrow things down.

Member Avatar for dmacdougall

Thanks Ric

Member Avatar for Rik_

if you should need any help with testing the monitor, let me know!

Member Avatar for dmacdougall

Will do. However, I'm on the road for the next week. I'll post whwen I return.

Member Avatar for Rik_

No problem!

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