Repairing Flat-panel monitors

Apr 1, 2009 12:00 PM, By John Landry, CSRE

Flat-out repairs

Flat LCD screens are now the standard for most desktop workstations and TVs. They are certainly easier to carry and set up than their old CRT counterparts, but my experience has shown that they don’t hold up well in a 24/7 operation. We have several Samsung Syncmaster 940 TVs that went into service at the end of 2006 and have already failed. Most of them stop working because the capacitors in the little switching power supply burst open.

The capacitors chosen for this TV were some of the smallest available. While they were rated for 105� C operation, they were not low ESR types, which compounded the problem. Most of these TVs have been repaired by complete replacement of all of the capacitors on the power supply board. The United Chemi-Con Type LXY and KMG have been used as replacements with great success.

One Planar desktop monitor needed not only a power supply rebuild but also new backlight tubes. These tubes are very small fluorescent light bulbs housed in a plastic slot in the rear of the display. JKL Components makes the bulbs, which are available through Digi Key. While these bulbs come in many lengths and nine different diameters, virtually all of them draw the same amount of current per tube (5mA). Most of the lamp driver boards have an adjustment pot and usually after adjusting it the screen works again.

Landry is an audio maintenance engineer at CBS Radio/Westwood One, New York.

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