Need some help with a MAG LT782s LCD

[Psyfer]

Re: Need some help with a MAG LT782s LCD

bump

[PlainBill]

Re: Need some help with a MAG LT782s LCD

LOL. Well, that sucks. Do you think its the CCFLs? If so, where do I get some new ones, eBay?

At this point you have reduced the possible causes to the CCFLs, the wiring to the CCFLs, or a problem with the protection circuit.

The best way to troubleshoot this is to take an entire LCD panel with identical connectors and hook it to your inverter. If the CCFLs stay on, the problem is either CCFLs or the wiring to the CCFLs. This can be further troubleshot by substituting one CCFL from your LCD panel for the CCFL in the test panel (it's not necessary to remove the CCFLs from the panel, just plug the connector into the inverter).

Another way is to take a known good CCFL and substitute it for each original CCFL in turn. When the CCFLs stay on, you have identified the bad one.

A third way is to disconnect three of the CCFLs, then turn on the monitor. The backlights should come on (dimmer) for two seconds. Disconnect that CCFL, and hook up another, then turn on the monitor again. Continue this until you identify one CCFL that does not light. Then it's time to tear down the panel.

CCFLWarehouse is one source; the also have an eBay store, Plasmo Industries.

PlainBill

[mallwood]

Re: Need some help with a MAG LT782s LCD

Dang!!!

There are two thing I ould like you to try.

The first is safe. Measure the resistance between the two points circled in black. Measure the resistance between the two points circled in yellow. These are the secondaries of the transformers. They should match within 3%.

The second gives me the heebie jeebies. Hook up the boards and connect one pair of CCFLs to the output connector. Leave the other pair disconnected. Turn on the monitor. Does the backlight come on? Turn off the monitor, disconnect the first pair of CCFLS, connect the second pair, and turn on the monitor again. Does the backlight come on?

If the backlights come on at the same brightness in each case (I understand it will be difficult to judge brightness), repeat the test, but hook up only one CCFL at a time. You are looking for one (or more) CCFL that does not light.

PlainBill

Hi, I too was having the off-after-two-seconds issue with the backlight mentioned in this thread, and I did the tests mentioned above.

One of the transformers (the top one) gives an open circuit on the secondary winding, while the other one gives about 350 ohm.

Both the lamps seems to be working (only for two seconds tho) if I connect them with the bottom connector once at the time. They do not work when connected to the top connector, so I guess the lamps themselves are OK.

Is the only way to repair this to replace the broken transformer? Or would it be possible to bypass it and only use one lamp? Even if that gives me less brightness.