Hp L1925 lcd monitor black screen

[mats23]

Re: Hp L1925 lcd monitor black screen

Fine, I`ve took pictures from the inverter board now. it has been previously fixed.. or that`s how it looks.. the blue wire goes to pin no 3.

[selldoor]

Re: Hp L1925 lcd monitor black screen

Well thats a bit of a mess can you clean any of it off with Isopropyl alcohol.

Pins you need to check are S1>S2 and S3>S4
Power OFF Meter on ohms 2000 - post results.

[mats23]

Re: Hp L1925 lcd monitor black screen

Either the meter i have is not good.. either the component is with problem... i do not get any numbers

[selldoor]

Re: Hp L1925 lcd monitor black screen

It may be lacquer or flux on the connections you will need to dig into the solder.

On that setting what do you get when you touch the probes together?

[mats23]

Re: Hp L1925 lcd monitor black screen

- .006 to - .010

[selldoor]

Re: Hp L1925 lcd monitor black screen

Ok - it is fairly unusual for both transformers to be blown.
Can you disconnect the inverter and take it outside and try to get some
decent pictures of it - close up on the repair and the ends of the transformers where you are testing.

Just as another test on your meter - in your picture of the power supply top left
there is a big green resistor can you measure that and check with the colour bands if
you get the correct resistance.

[mats23]

Re: Hp L1925 lcd monitor black screen

The resistor beeps when on continuity.... on 200 shows 00.4 00.5 00.3 the lines on it are yellow red silver gold and black.

which is the inverter?

[selldoor]

Re: Hp L1925 lcd monitor black screen

Sorry - missed a word out - meant to say Inverter board. That is the one with the inverter transformers on it.

[selldoor]

Re: Hp L1925 lcd monitor black screen

The resistor beeps when on continuity.... on 200 shows 00.4 00.5 00.3 the lines on it are yellow red silver gold and black.

I am not sure your meter is correct - it should not be wandering on an ohm check.
Here is the link for a 5 band resistor- cant get your colours to fit? you have a go.

http://samengstrom.com/15924820/en/r...14782,15924820

[mats23]

Re: Hp L1925 lcd monitor black screen

Here you go... the inverter board.



the resistor... is 0.42 ohm with 5% tolerance.

you can see it under 4 bands resistance but mine has also a thin black line after the golden...
http://www.hobby-hour.com/electronic...calculator.php I have used this site, but it says it`s not standard and it`s calculated as a 4 band resistor

[selldoor]

Re: Hp L1925 lcd monitor black screen

OK your meter is working correctly - try checking the transformers again.
you should be looking to get between 400 and 2000 ohms on the secondary
windings- if they are open then they are dead. - Have they got numbers written along the edges.

[mats23]

Re: Hp L1925 lcd monitor black screen

Both measured between 500 and 600 (~575); no, they do not have numbers on their edges.

[selldoor]

Re: Hp L1925 lcd monitor black screen

Well that is better, but we need the exact measurements as the test is that they should be within 3% of each other

[mats23]

Re: Hp L1925 lcd monitor black screen

just a question.... since i have got 2 1000uF 16v caps bught.. and all the tools necessary to replace... may I replace the 2 rubycon caps...? What is the probability to be broken?

[mats23]

Re: Hp L1925 lcd monitor black screen

They are 573 and 574-5.

[selldoor]

Re: Hp L1925 lcd monitor black screen

Excellent! - I dont think it will be the caps but change them if you want- it may be that.

Can you check the two brown resistors at each end of the Board One is R21 cant make out the other.
Also can you check the repair using continuity from the pin in the socket to pin 3 (Use the pin not the solder) Also check it is not touching pin 2 or anything else.

I dont know if It has been mentioned but there is a fuse on the inverter board as well - (see what a difference good pictures make) Can you test it- Ohms 20 probe on each end.
Perhaps Budm will be back later and he might suggest where is best to do voltage checks on the board.

[retiredcaps]

Re: Hp L1925 lcd monitor black screen

If the backlight doesn't come on at all, not even a flicker or brief flash, it is either a blown fuse that selldoor mentioned or your mosfets (Q4, Q5, Q6, and Q7) are shorted.

Testing for a shorted mosfet instructions at

https://www.badcaps.net/forum/showpo...4&postcount=19

[selldoor]

Re: Hp L1925 lcd monitor black screen

This might come in useful later.

It is also noted that it is very similar to the viewsonic VP191- looks like same power supply and same inverter

[mats23]

Re: Hp L1925 lcd monitor black screen

I dont know if It has been mentioned but there is a fuse on the inverter board as well - (see what a difference good pictures make) Can you test it- Ohms 20 probe on each end.
Perhaps Budm will be back later and he might suggest where is best to do voltage checks on the board.

Which one is it? can`t see it.

Which is the mosfet?

[selldoor]

Re: Hp L1925 lcd monitor black screen

Attached Pic - What are the part numbers on the mosfets