HP w20 LCD Display Inverter, running out of options.

[seanc]

Re: HP w20 LCD Display Inverter, running out of options.

I spy another cap, has it been changed?

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

I spy another cap, has it been changed?

There are 3 caps in this board I have not changed. One you spotted is on another side of big transformer with it's buddy and then there its the small one near big caps (first image). Maybe they need to be changed too?

I also changed one cap from logic board (or whatever it's called). There was a 100uF 25V cap I could not believe was what it said because it was so small. So I replaced it with nichicon that had same values but size much bigger (3rd image). There is also 1000uF 25V cap on the board which I suspect can't be what it says. It's so tiny.

The twirling sound is back and it may come from that choke (L106) under schottky. How can I identify what kind of replacement I may try?

I did some timings today. With brightness set to 35 it operated 2 hours and five minutes. I restarted it immediately and it worked for another 25 minutes. Then it went to 2 secs to black and needed about half an hour in peace. Backpanel was in place to keep heat inside.

[retiredcaps]

Re: HP w20 LCD Display Inverter, running out of options.

That is the one (with blue arrow) I was asking about hiding underneath the heat shield in the earlier post.

I spy another cap, has it been changed?

[retiredcaps]

Re: HP w20 LCD Display Inverter, running out of options.

You might as well change the other 3. Non bulging caps may still be bad. I personally can't justify spending $50+ for a ESR tester as this is a hobby, so changing 50 cents caps is more $$$ justified even though I hate blindly changing things.

I have NEC 1700V that goes 2 seconds to black and the logic board has seven Capxon 680uF 25V 105C caps that are 10mmx12.5mm. This size is very hard to find so I believe a cap can be 1000uF and 25V and be very small.

BTW, what is the diameter and height of the 100uF 25V cap in mm? Let's see if we can get a proper size fitting one instead of that sideways blue one?

Do you have a magnifying glass to double check all the solder joints around the L106 area?

There are 3 caps in this board I have not changed. Maybe they need to be changed too?

There is also 1000uF 25V cap on the board which I suspect can't be what it says. It's so tiny.

The twirling sound is back and it may come from that choke (L106) under schottky. How can I identify what kind of replacement I may try?

[seanc]

Re: HP w20 LCD Display Inverter, running out of options.

That is the one (with blue arrow) I was asking about hiding underneath the heat shield in the earlier post.

I thought it was, so I pointed it out :P

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

That is the one (with blue arrow) I was asking about hiding underneath the heat shield in the earlier post.

Sorry I misunderstood you (and thanks seanc). Now I checked from below and board is divided into 3 sections. That cap is within AC 220V section so I figured out it's probably irrelevant as I get 5V and 14V even after problem occurs.

You might as well change the other 3. Non bulging caps may still be bad. I personally can't justify spending $50+ for a ESR tester as this is a hobby, so changing 50 cents caps is more $$$ justified even though I hate blindly changing things.

I agree and I think I will. I may change all caps on logic board too. I think total cost will be less than $5.

I have NEC 1700V that goes 2 seconds to black and the logic board has seven Capxon 680uF 25V 105C caps that are 10mmx12.5mm. This size is very hard to find so I believe a cap can be 1000uF and 25V and be very small.

Original 100uF was 12,5mm x 8mm but somehow I think bigger is better so I don't mind if I need to bend their legs

I also resoldered L106 area and just in case replaced nearby bottom size resistors too just in case heat may have defected them but nothing seems to help.

Last test: With brightness set to 90 it operated 45 minutes. So lower brightness seems to give more operating time.

[retiredcaps]

Re: HP w20 LCD Display Inverter, running out of options.

From what I read here on the forum, it is important to match the original cap specs in terms of ripple, uF, and voltage. Size doesn't matter IF you have the room for a bigger cap. AFAIK, bigger doesn't mean "better".

Just a quick glance on digikey shows multiple 100uF 25v caps that are around the size of the original.

Re: the run time. I'm just not experienced or knowledgeable right now to know what to check for. It seems to me that something in the circuit is getting to a temperature threshold when it runs longer and then cuts off to protect the system. If there was only a way to put multiple probes in the circuit to set off an alarm or something, this would be a lot easier to troubleshoot.

Hopefully, one of the experts can add something from a past case history?

Original 100uF was 12,5mm x 8mm but somehow I think bigger is better so I don't mind if I need to bend their legs

[retiredcaps]

Re: HP w20 LCD Display Inverter, running out of options.

On the non circled red solder joints, do they look okay?

P.S. In attached image red ones resoldered, green ones replaced.

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

I think I've resoldered most of them several times already. Now I tested to change L106 to another side to reduce it's heating. That did not help either. I noticed from this picture that R42 seems to be disconnected by CP6. Could this be manufacturing defect.

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

Another observation, could this be a bad capacitor? There seems to be something red on sides of it.

[seanc]

Re: HP w20 LCD Display Inverter, running out of options.

Glue, probably.

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

Looks like this one is finally solved. Thanks for everyone contributing to this thread. Today I've been using this monitor for almost 5 hours and it's still working without any problems. Thanks tothis link by retiredcaps on another thread I started wondering if it still could be bad solder joint on some transistor.

As the dude on the video has beard pretty much like mine, he must have some better knowledge about these things. Great logic is it not . So I just had to try it. I soldered all those tiny transistors again as I had no clue which transistor could be the one causing this problem. There were something like 10 to 15 on the board so it was not that big deal to solder them all. And now the monitor works like new one.

Next I am going to buy a good magnifying class. I'm sure that next time it will save me some time and money to verify all solder joints thoroughly before purchasing any caps or other components again.

[retiredcaps]

Re: HP w20 LCD Display Inverter, running out of options.

I learned quite a bit from the "fixes" on youtube. Anyways, another thread suggested that instead of resoldering or reflowing the "old" solder to remove all the "old" solder and use new fresh solder for poor solder connections.

Glad to hear you got it working!

My soldering skills are still improving, but I'm going through tips like crazy. I managed to desolder some very small caps, but the holes are all plugged with the old solder.

Looks like this one is finally solved. Thanks for everyone contributing to this thread. Today I've been using this monitor for almost 5 hours and it's still working without any problems. Thanks tothis link by retiredcaps on another thread I started wondering if it still could be bad solder joint on some transistor.

[PlainBill]

Re: HP w20 LCD Display Inverter, running out of options.

I learned quite a bit from the "fixes" on youtube. Anyways, another thread suggested that instead of resoldering or reflowing the "old" solder to remove all the "old" solder and use new fresh solder for poor solder connections.

Glad to hear you got it working!

My soldering skills are still improving, but I'm going through tips like crazy. I managed to desolder some very small caps, but the holes are all plugged with the old solder.

There are several ways to solve this problem. My favorite is a 40 year old dissecting pick - a slightly tapered steel needle in a wood handle. I melt the solder to remove the old cap, then reheat it and use the dissecting pick to clear the hole.

PlainBill

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

To help people with similar problems with HP w20: Here is the image of what I resoldered, some of these did the trick. Total of 60 solder joints

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

It looked like I got this monitor fixed. But no, the problem came back. Luckily I got similar monitor so now I'm able to compare working one with this problematic one. Currently monitor stays on for about one hour and then 2 secs to black starts.

I could really use some directions as I really have no idea what to do next.

So far I've found out that:

- Problem is certainly within the inverter board. Changing board from one monitor to another switched the problem to there too and after using good monitors inverter board on failing one I'm sure that CCFL's are allright.

- All caps have been changed.

- Both shottcky's have been changed.

On working monitor I have REV 03 board and failing one is REV 02. There are some desing changes so I put images of both ones here. Maybe some wiser man could take a look at them and make some suggestions for me what I could try out next. Is there anything I could measure?

P.S. I noted that under schottky mbr20100ct there is a "big" change in resistance near that small cap. Rev 2 board gives 50 ohms from cap to schottky's anodes (2 x 100 ohms on top of eachother) and rev 3 board only 25 ohms (2 x 50 ohms side by side). I wonder what's the purpose of that as other parts on another side of board are identical.

[alexanna]

Re: HP w20 LCD Display Inverter, running out of options.

Man sounds like you have coverd all bases on this one.
I would still concider a bad solder joint .I quickly read the thread so is I mention something you have already done I am sorry.
I have had some fairly good luck slightly flexing the circut board with the tip of my volt meter lead in various places to locate solder joint problems,I have found some that I could not find with my eye ball.
You might also wiggle any capacitors you have replaced and see if you can see any movement in your solder joints.
Good luck Al.

[Aruba]

Re: HP w20 LCD Display Inverter, running out of options.

Do you have access to a can of freeze (cold) spray ? This could narrow the
component or the area that is heating up and causing the shutdown. On the other
hand a heat gun with a narrow exhaust vent can help narrow the area of what is
causing the shutdown much faster than the 1 hour you are waiting now until it
happens. A hair dryer could help also if you do not have a heat gun. Once you find
the area or component you can alternate using the freeze spray can and the heat
gun and see if the problem comes and goes.

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

Thanks Alexanna and Aruba. I've done heating / freezing without any success.

I wonder if some component(s) in the sense circuitry is bad/wrong or failing after enough heat is generated.

Problem is that I have no idea what or where is sense circuitry.
or am I looking at it?

I also wonder why R12 - 0 ohms have been changed to 1000 ohms on that line going to logic board in REV 3 board.

[Aruba]

Re: HP w20 LCD Display Inverter, running out of options.

A few questions:
- When you did the heating and freezing you say "without any success",
does that mean it still takes 1 hour before the monitor shuts down ?
- Does it take longer to shut down if the brightness is set at ~10% vs 90% ?
- Once it is shut down, can you turn the AC power off then back on immediately and
does it take yet another hour before it will shut down again ?
- Once it is shut down, does freeze spraying make it recover ?
- Are the main voltages like 5V, 12V from the P/S still present when it is shut down ?

On the rev2 to rev3 question, it looks like there was a functional change needed on
the rev2 boards and was reworked into them. The rev3 boards has this "rework" all
layed out neatly with etch on the pcb. To know the reason why they did this is going
to be hard to find out unless you can get hold of the service bulletin or ECO
(engineering change order). This change is not your problem at this moment. This
monitor was working x years before it failed. What you need to find out what has
failed and replace it/them and first have a working monitor. Then you can go and
investigate (if you want to) what this change is between rev2 to rev3 and decide if
this change affects your specific situation. Changes are sometimes specific like you
only need this change if you are operating the monitor in 35-40 degree C ambient.