Fujitsu monitor: power is there, but no image from PC

[jvelez]

Re: Fujitsu monitor: power is there, but no image from PC

Disconnect the CCFLs backlights and wire a regular twist household CFLs (without the electronic ballast) to the inverter. Turn it on and see what happens.

Thank you CapLeaker! Just to be sure I understood it right: in the old days, I used to test the tuning of the my homemade short wave transmitters by touching with one pin of a domestic FL in the final stage/coil (the anode tension of the tubes was enough to trigger the initial discharge of the gas, and the lamp would become more or less bright as I tuned the final RLC stage). Here, you mean actually connecting one of the CCFL outputs to the pins of one side of the lamp, right? Thank you and sorry for likely dumb question...

[CapLeaker]

Re: Fujitsu monitor: power is there, but no image from PC

Yes. You got 2 outputs on this inverter. Take two old CFLs just a smallish one like 6 or 10 Watts, take the ballst off and you will end up with a twisty bulb with 2 thin wires hanging on each side. Now twist the 2 wires hanging on each side together, so you end up with a twisted wire each side of the CFL. Now connect the blue and black wire from the inverter output to the 2 legs of the CFL. Same thing on the second output of the inverter. Turn the thing on and Bob is your uncle.

[jvelez]

Re: Fujitsu monitor: power is there, but no image from PC

Finally got some time to go back to the Fujitsu-Siemens monitor, and the problem is solved, it came back to life!
The problem resided in one of the (4) NPN power transistors that drive the line transformers who drive the CCFLs. I substituted all 4 transistors, and the monitor is now working perfectly.
For future memory in this Forum, here goes some highlights of the whole journey:

Problem:
When the monitor is switched-on, it shows briefly the Fujitsu-Siemens logo for about one second, and then the screen goes black.

Additional info:

• Two boards inside the monitor: main board is 715L1019-F and inverter board is 715L1109-1B-FS.
• Power supply is working, correct voltages measured on the key point of the circuit.
• Power led switches between blue and amber, thus recognizing when input signal is present.
• No Service Manual found anywhere in the Net, despite all searches.

Actions taken

• Nothing abnormal found on main board: no cold solderings or bad capacitors, power supply tensions correct.
• More experienced people in this Forum directed my attention from the main board to the inverter.
• The key question was: are the CCFLS still illuminated after this brief "one second" of activity? No, they go off.
• Measured voltages correct at the inverter input/connector
• All electrolytic capacitors replaced in inverter, but the problem still persisted.
• Power transistor replaced (2SD1691), and voilà: monitor is working

My deepest THANK YOU to all the members who helped me spotting the problem!
.