Another HP L1740 has died

[George Ortiz]

Well,
Over the weekend one of our company's L1740 has died. Classic 2 seconds to black. I'm gonna replace the CCFL's on this one first before even looking
at the power supply. I know that the power supply has bulging caps from experience with this model of HP monitor. Lucky for me I have two spare repaired power supplies.

[Krankshaft]

Re: Another HP L1740 has died

CCFLs should always be the last thing you check don't guess gather evidence.

If that monitor shares the design with my L1955 then one of the inverter driver transistors could be shot.

Even though these boards were packed with Elites on the 9 or so I serviced they were never bulged but I replaced them preemptively.

On a rare occasion (only once) I had the signaling transistor shorted on one of the blown the 4431 On / Off FETs causing 2 seconds to black. It was holding one side of the inverter off via the FET causing the protection circuit to kick in since only one side of the inverter was running.

This was covered in my HP monitor repair guide thread.

If you have a repaired PSU on hand swap it in if it still goes to black then you can look to the CCFLs.

CCFL replacement is easier some displays than others just keep the layers of polarizing film and the LCD panel together these displays were assembled in a clean room. If you get dust in between the layers you will never get it out and they will manifest as dark blotches on the screen.

[George Ortiz]

Re: Another HP L1740 has died

Just when I've seen it all. This monitor has a Power/Inverter board model E58528 TCI-AjS D 94V-0. I see at least two blown Su'scon 470 uf
25V Caps. Now there are four types of power supplies for this series of
HP L1740 monitors. Phillips, 715g1955-1, BenQ and now this one.
The model number that's on the lead side of the power board is 490481400100R (QLPI-003 Rev. A 2005-10-11) and the logic board is 490481300101R
(QLIF-054 Rev.A 2005-10-11). I'll replace all the caps except for the large
100 uf 425v capacitor. Checked the two transformers T1 and T2 and will
have to resolder. Looks like bad/cold solder joints inverters. Once I have
the power supply board repaired (??) will let all know how it goes. BTW all
the caps are Su'scons.

[George Ortiz]

Re: Another HP L1740 has died

It's alive. Well replaced the caps on the power supply and it works.
Works like a champ!!!!!!