Hp l1940t no power

[electrobe]

I have a HP L1940T LCD Monitor that doesn't power up & doesn't make any sounds. I looked at the circuit boards & I visibly see no signs of damage. I measured the voltage coming from the socket where the power cord is plugged in & it had the proper voltage. I do not no what to do next & would appreciate any help provided.

[budm]

Re: Hp l1940t no power

OK, I need in focused pictures of the bottom side of the board and the Main board again.
Chek the fuse (white cylinder), and then check the voltage on that large cap, be real careful since you will be working on the hot (line) side of the circuits.
Post picture in the using advanced, attachment function.

[electrobe]

Re: Hp l1940t no power

Here are more photos for you. Let me know if you need more. I will check the fuse.

[electrobe]

Re: Hp l1940t no power

I tested the large ELCAP 100UF M 450V as you have suggested & the DC voltage was 171.7 Volts. The 3.15A 250 vac fuse when I set my multimeter to ohms read 000.0

[jetadm123]

Re: Hp l1940t no power

Fuse and voltage across cap look good. I know you said the monitor doesn't power up, but you do get any activity from the power LED on the front panel?

[retiredcaps]

Re: Hp l1940t no power

What are the DC voltages on all the pins of connector CN951?

[electrobe]

Re: Hp l1940t no power

There is no activity on the LED front panel. I checked the DC voltage all the pins of connector CN951 and I got 2.92V on pins 6 & 7, 0.012V on pins 3 & 4. When i measured a 2nd, 3rd & 4th time I got the results of 0000 across all pins.

[jetadm123]

Re: Hp l1940t no power

Try measuring the voltage across the small cap c927 located in the middle of the power board.

[budm]

Re: Hp l1940t no power

This a service manual that matches your chassis.

[electrobe]

Re: Hp l1940t no power

I went back and measured the small cap c927 located in the middle of the power board and I got a result of over voltage 0.L. Thanks to Budm providing the service manual I also measured the voltage for the pin8 of IC901 and got a result of 0.L over voltage. Does this mean my board is toast?

[budm]

Re: Hp l1940t no power

Please recheck the batteries in your meter and also try measuring something like a AA batteries or a 9-Volt batteries. It looks like the power supply not siwtching, need to do more components testing, but let's verify the meter first.

[electrobe]

Re: Hp l1940t no power

I did as you had ask & checked a AA battery to make sure the meter was working properly and it was.

[retiredcaps]

Re: Hp l1940t no power

I did as you had ask & checked a AA battery to make sure the meter was working properly and it was.

Post a picture of your multimeter. 0L implies you are likely using an autoranging multimeter. For it to display 0L, the voltage would have to be over 1000V DC.

Most manual range multimeters show a "1" on the left hand side to signify out of range.

[electrobe]

Re: Hp l1940t no power

Here is the photo of my auto ranging multimeter that you have requested. I will go back & retest c927 & voltage for the pin8 of IC901.

[electrobe]

Re: Hp l1940t no power

I went & remeasured C927 (results 0004 V) (which is a 68uF 25V capacitor) & IC901 pin8 (results 0162V). The capacitors on this board are from the manufacturer Elite. I removed the decimal in my auto range multimeter.

[jetadm123]

Re: Hp l1940t no power

I went & remeasured C927 (results 0004 V) (which is a 68uF 25V capacitor) & IC901 pin8 (results 0162V). The capacitors on this board are from the manufacturer Elite. I removed the decimal in my auto range multimeter.

Retiredcaps is more an expert on meters than I am, but since you indicated no decimal points in your readings, it appears that the meter is set to too many signifcant digits. In other words, pin 8 should show 162.XX Vdc and C927 something like 4.XX Vdc.

4 volts across C927 is too low a start voltage for IC901. You need a minimum of 10V. I would try changing C927 to see what happens.

[electrobe]

Re: Hp l1940t no power

I finally had a chance to get back to the power board & replace C927 with a new one & remeasured the voltage. It jumps back & forth from 9V to 10.40V. I have no clue where to go from here. I would appreciate any input that could be provided.

[retiredcaps]

Re: Hp l1940t no power

It jumps back & forth from 9V to 10.40V.

Disconnect all the boards and just test the power board by itself.

Does the reading still fluctuate?

[electrobe]

Re: Hp l1940t no power

Yes the voltage still fluctuates when tested.

[retiredcaps]

Re: Hp l1940t no power

Follow the steps on page 21 using budm's pdf file.