Member Avatar for mahela007

hi.. I have an acer 23" LCD monitor. When the computer switches to UPS power, (for eg if I turn of the power from the wall socket) i hear a moderately soft buzzing noise comming from the monitor. What could the cause of this noise be?
The noise is there even when the monitor is in standby mode.

(I'm running the screen at very low brightness and contrast if it's relevant.)

Edited by mahela007 because: n/a
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Dani AI

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Brief expert note adding practical checks and fixes.

Given the behaviour reported by (buzz present only when the UPS is on battery) and the waveform concern raised by , the most likely mechanism is vibration of the monitor's switching components or small inductors being excited by a harmonic-rich UPS output. The following focused tests and mitigations were not covered in the thread and help narrow cause or eliminate the noise.

  • Isolation test: power only the monitor from the UPS (disconnect the PC and any signal cables). Persistence of the buzz with the monitor alone points at the monitor PSU/magnetics; disappearance points at an interaction between devices.
  • Load test (safe, controlled): with the UPS on battery, add a modest resistive lamp (well below UPS capacity) to change the UPS load. A change in the noise level indicates the UPS output shape is load-dependent. Do not overload the UPS.
  • Cable management: keep the AC lead and video cable physically separated and clip-on ferrite cores to the monitor power and video cables to reduce conducted/radiated coupling.
  • Ground check: confirm the UPS earth is intact and not floating; poor grounding can worsen audible EMI. Use a multimeter or the UPS/manual for safe checks.
  • Long-term fix options: a line-conditioner or a UPS that explicitly lists "pure sine wave" or "online double-conversion" output removes most harmonic content and typically cures this kind of buzzing.
  • Service/ safety note: audible coil-whine or loose magnetics can also come from the monitor itself. Do not open the monitor unless qualified; contact the monitor vendor if under warranty.

Short-term exposure rarely causes immediate catastrophic failure, but harmonic-rich supply can increase stress on switching components over time. For reliability in battery operation, a true sine-wave UPS or professional repair is the definitive solution.

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Member Avatar for Suspishio

The buzzing normally changes if you change brightness/contrast. It should reduce buzz if brightness is turned up.

I'll make an informed guess here.

I think it's coincidence - you're running on low brightness so there's a buzz.

But I can't ignore the UPS point. I'd bet that the UPS (maybe a cheaper one?), without proper mains synchronisation (50Hz in the UK, 60Hz in N. America) the UPS A/C output is not perfectly sinusoidal which can induce the buzz via the input mains component. I would expect the buzz to disappear if you turn up the power demand via the brightness control, but that depends on the monitor's design.

Member Avatar for mahela007

you seem to keep answering all my threads... thanks.
the buzzing doesn't go away with high brightness settings... Can it damage my monitor?

Member Avatar for Suspishio

No it won't damage anything if my diagnosis is correct - i.e. on battery driven UPS only. It means that the sinusoidal interference or drift is causing an electrical resonance that comes out in a buzz.

Outside chance it'll go away if you separate mains and video cable - no overlay. I've seen that before on CRT monitors.

And you can confirm that it goes away when your UPS is mains connected? Yes? If not then you do need to contact your seller because something would be wrong.

Member Avatar for mahela007

yeah... When the UPS is connected to the mains the buzzing does go away.

Member Avatar for Suspishio

Please mark this thread as SOLVED. By the way, what make/model is your UPS? It's a matter of interest to know which UPS brands have imperfect sinusoidal output.

Member Avatar for mwadime

Please mark this thread as SOLVED. By the way, what make/model is your UPS? It's a matter of interest to know which UPS brands have imperfect sinusoidal output.

my laptop is pledging for the instalation of a HI speed USB host controller......wat shud I do?

Member Avatar for Suspishio

my laptop is pledging for the instalation of a HI speed USB host controller......wat shud I do?

Please start your own thread and provide full details of what is happening.

I realise that English is not your first language but what you have asked unfortunately doesn't make sense.

What are the circumstances?
What messages do you receive?
What laptop?
What Winodws version?
What needs a high speed USB controller?
Is your laptop broken and a USB controller has failed?

Full information please in your own new thread.

Member Avatar for mahela007

Please mark this thread as SOLVED. By the way, what make/model is your UPS? It's a matter of interest to know which UPS brands have imperfect sinusoidal output.

It's a prolink UPS... I don't know if it's right to but a black mark on the whole brand. This IS a low end UPS so maybe it's just this model.

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