Hp 1940 flicker

[selldoor]

Re: Hp 1940 flicker

Resolder all these top side (main component board side) solder joints yes?

These are the main components you need to resolder. They are ringed in red
on the top of the board but you need to solder all of their contacts on the bottom of theboard.

That was what I was going to say but had to dash out -sorry.

They are mostly related to lighting the backlights and can pump out up to 1000volts so need treating with respect. You may have to do some resistance checking on them later. (without power connected)

Those voltages look ok I will wait for you to report back if there is any improvement before trying to find the IC Data.

[terminatorX]

Re: Hp 1940 flicker

I see that resoldering is very important in this case. Was waiting a bit becuase I got two screens so If I need to buy anything I would like to take it in one batch...

Here are my pictures on IC701

[Hunt]

Re: Hp 1940 flicker

I see that resoldering is very important in this case. Was waiting a bit becuase I got two screens so If I need to buy anything I would like to take it in one batch...

Here are my pictures on IC701

Very good picture; we all now know the chip number.

[Hunt]

Re: Hp 1940 flicker

These are the main components you need to resolder. They are ringed in red
on the top of the board but you need to solder all of their contacts on the bottom of theboard.

That was what I was going to say but had to dash out -sorry.

They are mostly related to lighting the backlights and can pump out up to 1000volts so need treating with respect. You may have to do some resistance checking on them later. (without power connected)

Those voltages look ok I will wait for you to report back if there is any improvement before trying to find the IC Data.

I have been testing this monitor for a couple of days now and it has not flickered and the text looks sharper better than ever.

Throughout this test, the plastic back and front bezel have not been fitted.

I wonder if the air slots in the plastic back have the same area as the metal chassis. Could poor ventilation be a problem?

In any event, currently just re-soldering the entire top side transformer connections as directed has done the job.

One caveat I must add is that the repair is not proven as the monitor is not fully assembled or being used in the same way as it was when the intermittent fault occurred.

From all the above I conclude the TerminatorX should follow the advice given by Selldoor before doing anything else.

[selldoor]

Re: Hp 1940 flicker

Thats great news. Switching on and off hot/cold will be the real test.
Lack of ventilation is probably the main killer of monitors. It affects the solder and dries out the caps - I always try to use 105degree caps when replacing any. I have seen some people cut extra holes in and even add fans - depends if you can put up with the extra noise. Anyway I hope it continues to work for you.
I cannot take the credit for "fix" which was passed on from and mentioned by others in the thread, but perhaps a little for the persistance.

[terminatorX]

Re: Hp 1940 flicker

Ok a brief update.
I desoldered the transistors.
I followed :http://www.youtube.com/watch?v=8VK_4gZU__I
3 of them showes exatcly same conducting pattern in diode mode.
On the vid he has about 0.500 and I have about 0.600 where it should read.
The fourth one though must be broken. It displays like 0.004 in either direction and on places it shouldn't display anything.
Just a little concern the desoldering was a little clumsy since I didn't have proper tips and hope the temperature isn't of big concern for the transistors.
I guess I'll do a turn on ebay.

[selldoor]

Re: Hp 1940 flicker

Have you resoldered this board yet?

[Byeelectric]

Re: Hp 1940 flicker

All,

I have this issue/repairing for my friend. I am an old school technician and can tell you to change all C5707 transistors and the two Field Effect Transistors near the ballast transformers. You may also need to change the dual schottky diodes (two transistors mounted on the heat sink). The flicker is on and off due to improper regulation on the ballast side. I have four of these to repair/this is the second time because I did not change the FET's. I currently have one on "Burn in" for 24hrs. Email me if you need any addiditonal info. P.S. I check my email three times a week so please have patience.

[Hunt]

Re: Hp 1940 flicker

I spoke to soon
Now I am using the monitor more like I did before it has flickered. It is not a bad and if I leave it a moment the screen settles down and works ok.

I'm using the monitor without the case still; is that safe?

[selldoor]

Re: Hp 1940 flicker

I'm using the monitor without the case still; is that safe?

Safe in that it wont damage the monitor - yes.

Safe to work with? as long as you are fairly careful ,not throwing coffee over it
no children attacking it, etc then reasonably safe. If its something you can do easily try it with the ccfl leads swapped and see if it makes any difference.
As cffls get older the one at the top of the screen usually becomes less efficient than the bottom one as it is exposed to more heat. This imbalance could make it flicker.

[Hunt]

Re: Hp 1940 flicker

Safe in that it wont damage the monitor - yes.

Safe to work with? as long as you are fairly careful ,not throwing coffee over it
no children attacking it, etc then reasonably safe.

Hmmm... Children could be about but under supervision.
I was thinking that since all the metal was on the screen and that metal is earthed I should be ok. In addition, I was hoping if I can get this monitor, working it could be one of three. Thus if there is no plastic bezel the gap between screens would be smaller. Not having the cover would make the screen last longer as well.

If its something you can do easily try it with the ccfl leads swapped and see if it makes any difference.
As cffls get older the one at the top of the screen usually becomes less efficient than the bottom one as it is exposed to more heat. This imbalance could make it flicker.

The flicker is a definite black screen then full text screen like blinking.
I have not yet soldered any connections on the printed circuit side.

Should I swap the cffls leads first?
or resolder?
I have the impression that moving/changing the ccfl's is not easy so is swapping the leads an easy job?
And where are these leads?

Thanks.

[selldoor]

Re: Hp 1940 flicker

Resolder First

The leads are in the 4 small white connectors along the side of the power board that has the 4 yellow inverter tranformers on.

[budm]

Re: Hp 1940 flicker

I would resolder the joints as suggested by retiredcaps, same problem in other DELL and HP monitors (they are made by BenQ).
Also check the two rectangular body gray caps for value and leakage otherwise you may blow up your transistors.
Same chassis as 17" version.
http://s807.photobucket.com/albums/y...HP/HP%20L1740/

[Hunt]

Re: Hp 1940 flicker

http://s807.photobucket.com/albums/y...HP/HP%20L1740/

Those photos are stunningly clear; have you a good camera or are you using some special lighting?
The board looks very clean.

[budm]

Re: Hp 1940 flicker

Ten years old SONY DSC-S70/S50, they have real good MACRO and LENS for really closed focus. Most new point and shoot camera cannot do less than 2" focus. I got these cameras from EBAY for $20, the memory stick is REAL expensive though.

[terminatorX]

Re: Hp 1940 flicker

Problem solved!

After a brief pause I resumed troubleshooting on this monitor. I just got the transistors from ebay. I resoldered back the old ones and just replaced the faulty one. That did not help at all. But I read the discussion you had about swapping the ccfl's. I saved some from another screen I had come across a couple of weeks back. Did this since I read somewhere about faulty ccfl but I did not think about it more until now. Unfortunatly it was smaller than the actual screen but I modified the ends a little(rubber ends). It really wasn't an easy task to remove all frames coming down to the ccfl's and watching not breaking the LCD plate. Anyway it's done and working like a charm. So now you know it's possible to use 15" ccfl's in a 17". Thought the lacking centimeters would do something but there is nothing showing any signs.
So any one else with this problem good luck and thanks for the help!

[budm]

Re: Hp 1940 flicker

Sometime I use lamp from 21" in the 22' panel, can hardly tell.
Good job fo figuring out, I myself have a lot of test lamps to use for testing.

[selldoor]

Re: Hp 1940 flicker

Great news!! Is it back to the 1955 now?

[terminatorX]

Re: Hp 1940 flicker

Yes now it's just the 1955 left and thanks =) To mention...the feeling of accomplishment is just awesome!

[Hunt]

Re: Hp 1940 flicker

I would resolder the joints as suggested by retiredcaps, same problem in other DELL and HP monitors (they are made by BenQ).
Also check the two rectangular body gray caps for value and leakage otherwise you may blow up your transistors.
Same chassis as 17" version.
http://s807.photobucket.com/albums/y...HP/HP%20L1740/

Well it has been nearly a week since I re-soldered all the underside joints in the area of the four transformers and near all the discoloured section of the board.

No flickering yet and I believe the use of the monitor is reprehensive of when it was faulty.

My only concern now is the comment above about... "Also check the two rectangular body gray caps for value and leakage otherwise you may blow up your transistors."
How do I test for the above?

I'm also wondering if drilling more holes in the metal cover of the same size (finger safe) as already exist but on the adjacent side to aid cooling?

Then putting more finger safe holes in the plastic back cover?

Thanks for your help so far people.