Member Avatar for tony elkin

Hi there gang, newbie here. Thanking you in anticipation of help. Am an ex engineer from the valve and magnetron days of radar so please feel free to get exceptionally 'tecchie if you feel the need!

Bought a used HP 15" flat screen and 12-15v power unit from a breaker, did not notice the small print which omitted the word fault and talked about a problem.... ok ok I know. He has refused a refund, and now I see that he has several for sale with the same fault.

Operates well apart form this specific thing. Ghosting is the wrong word as that implies limited overspill of a displayed item, however looking at the screen is more like looking at an old time B&W television with interference from another channel, or an interlacing scan problem. If it was a tube monitor I would say yes, a flyback problem, but it's a TFT.

There is a faint but discernable area across the whole of the screen width, in horizontal bands a cm or so apart, consisting of several lines at about 10 degress to the horizontal, which appears to move up and down at speed, bit like a wave. Both contrast and brightness controls affect the density and speed of movement from an inch a second to several inches a second.

Seasick making it is after a time.
It's not interference from adjacent equipment or cables, done all the repositioning tricks, and tried it on another PC so its not the video drive coming in, it seems to originate from the monitor.
The vendor admits a lot of monitors are like this.

My first thoughts are that something is oscillating at a frequency a few cycles away from something else and I am seeing the difference summation on screen. I have an oscilloscope at the ready, but no schematics as yet. Has anyone any suggestions on this as to where I start?

If it's fixable then there are quite a few flat screens out there that can be purchased at a reasonable price for repair!
Best regards
Tony E

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For — the moving, slanted bands that change speed and contrast almost always point to an internal timing or power problem inside the monitor rather than the PC. Useful, safe diagnostic order that does not repeat what’s already on the thread:

Start with the easy, low-risk checks: confirm the monitor is running at its native resolution/refresh from a second known-good source; try a different cable and input if available; use the monitor’s built‑in self‑test or OSD (if present) to see whether the artifact appears when the board generates its own pattern.

If the fault stays inside the monitor, open it only after unplugging and discharging capacitors. Visually inspect the power board and logic/TCON board for bulged or leaky electrolytics, cracked solder joints or damaged ribbon connectors. Gently reseat the flat flex and LVDS connectors and look for lifted traces where the panel harness meets the glass.

Oscilloscope checks you can do next (with strong safety cautions — earth‑grounded scope probes can short floating supplies): use a differential probe or isolate the monitor when probing LVDS/pixel clock lines. With a safe setup, check low‑voltage rails for low‑frequency oscillation/ripple while changing brightness; measure the pixel/gate timing signals at the TCON for jitter or missing channels. Tap the TCON and board edges lightly with a plastic stick while running to find intermittent joints. If the backlight inverter is separate, observe whether changing backlight settings alters the pattern — inverter noise can couple into timing circuits.

Probable fixes: replace failing electrolytics on the PSU, reflow cracked solder around the TCON/connector, or replace the TCON/main board (match part numbers on the panel). Panel harnesses and TCONs are panel‑specific, so use the panel’s stamped part number to source replacements or donor boards. For safety or if high‑voltage work is unfamiliar, have a qualified repair shop perform the power/inverter and scope diagnostics.

Note for : a green LED that flickers with no image usually implicates the PSU or backlight inverter and should be diagnosed along the same lines (rail checks, inverter presence), not the pixel timing circuitry.

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Member Avatar for dcc

I don't have any suggestions, but I would like to ask if this was purchased on Ebay?

Member Avatar for Kito67

I have problem with my Hp 1940 LCD color monitor screen 19" is product of china.This monitor when connected to the power shows that power is there by watching the LED indicator "Green" and then flicking thus so, and nothing is displaying on the screen. So, may i need your technical assistan what could be the problem and how is the technical procedure if i need to solve this kind of problem.

Its,

Aggrey Eusebio

Principal Instrumentation Technician.

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