HP L1955 with Benq 48.L1A02.A00 inverter

[michielvl]

I recently bought a secondhand HP L1955 which worked fine for exactly one month (doesn't really matter how long it worked since I have it because it is a secondhand, but anyways).

Then it went black and seemed not to detect the signal, after unplugging it sometimes worked for a while, sometimes not. I pulled the board and found one bulged capacitor (10v, 1000mf, at C709). I replaced it (16v, 1000mf, same heat rating 105 deg C) and it worked fine for 10 days.

Then, after about one hour, it went black. Turning it off (with the "soft" switch, not the main PSU switch) made the screen come back for a couple of minutes, then went black, switching off/on and so fort until the screen only stays on for a couple of seconds.

I opened it up again, but visual inspection didn't show anything wrong. Since, I am searching the internet for a possible diagnose, and I can tell you I, I have read almost every single post the common C5707 failure, this monitor and similar Benq inverter boards.

My question is: is this new problem likely to be caused by the C5707's? I know to assure i should test them, but right now I am using this monitor and it has been powered on (that is: without the cover, so it's getting less hot), for about an hour. So is it likely to be a 5707 faliure with heat or something similar? Or does it, from your experience, sound more like some sort of a capacitor failure?

Thanks for any thoughts, this forum has already helped me (a novice when it comes to electronics) to understand a lot about this monitor, inverter and its major problems, but right now i'm not able to make a judgement on what is likely to cause my problems.

EDIT: let me tell you i planned on checking with a strong light if the backlight's are turned off, but since I planned on doing so, the monitor didn't go black on me... When it did go black, the power light was on (green)

[Bobdee]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

I recently bought a secondhand HP L1955 which worked fine for exactly one month (doesn't really matter how long it worked since I have it because it is a secondhand, but anyways).

Then it went black and seemed not to detect the signal, after unplugging it sometimes worked for a while, sometimes not. I pulled the board and found one bulged capacitor (10v, 1000mf, at C709). I replaced it (16v, 1000mf, same heat rating 105 deg C) and it worked fine for 10 days.

Then, after about one hour, it went black. Turning it off (with the "soft" switch, not the main PSU switch) made the screen come back for a couple of minutes, then went black, switching off/on and so fort until the screen only stays on for a couple of seconds.

I opened it up again, but visual inspection didn't show anything wrong. Since, I am searching the internet for a possible diagnose, and I can tell you I, I have read almost every single post the common C5707 failure, this monitor and similar Benq inverter boards.

My question is: is this new problem likely to be caused by the C5707's? I know to assure i should test them, but right now I am using this monitor and it has been powered on (that is: without the cover, so it's getting less hot), for about an hour. So is it likely to be a 5707 faliure with heat or something similar? Or does it, from your experience, sound more like some sort of a capacitor failure?

Thanks for any thoughts, this forum has already helped me (a novice when it comes to electronics) to understand a lot about this monitor, inverter and its major problems, but right now i'm not able to make a judgement on what is likely to cause my problems.

Yes the C5707s can be problem for the 2 secs to black
But if its working with cover off that means they have not failed yet
suggestion if I may
Resolder the 4 inverter transformers and check the rest of board for bad solder joints also replace the other caps on the board, leaving out the big 400V one
The forum usually recommend Panasonic FC or FM series for replacement caps

[michielvl]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

Thanks for your fast answer! So if I understand correct, a 5707 failure is not really likely to be the cause, since (like now) it has been working fine for approx. 1,5 hours (without cover)? I will look into the soldering, but to be honest, I am waiting for it to fail so I can give it the "backlight-check" with a strong lamp to determine of it is just the backlights shutting down. When you're waiting for it to fail, it off course just keeps working!!


UPDATE: it has not gone black, but when switching it off and on, the capacitors make a terrible lot of noises. At least, the sound is definitely not coming from the area the 5707's are in. Switching off the main switch also leaves it sqealing for about 10 seconds. Now I will definitely replace the caps and resolder the whole.

[Bobdee]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

If you leave it then chances are it wil fail permanently and you may be replacing C5707s and a few other parts, even a possible Inverter transformer failure, you have been lucky up to now

[michielvl]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

You're right, turned it off and now using my backup monitor (at least 14yrs old NEC MultiSync M700, no problems whatsoever). I will replace the caps and update here.

To be sure: does this sqealing sound and the fact I can use the monitor for over an hour (without casing) mean there is nothing wrong with the 5707's? Or should I replace them anyway when I'm buying parts?

[Bobdee]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

You're right, turned it off and now using my backup monitor (at least 14yrs old NEC MultiSync M700, no problems whatsoever). I will replace the caps and update here.

To be sure: does this sqealing sound and the fact I can use the monitor for over an hour (without casing) mean there is nothing wrong with the 5707's? Or should I replace them anyway when I'm buying parts?

if it was still working when you powered down then C5707s should be okay
hopefully it was caps that was squealing, other things can squeal but best to recap first unless other members suggest something else
and resolder transformers (even if they look good) and anything else that looks bad

[michielvl]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

UPDATE: unfortunately I screwed up the board beyond repair I'm starting to believe. The copper trace lifted at two places, one was "fixable" using the not so pretty scraping and bending over the capacitor leg method.

But this is non-fixable I'm pretty sure as the copper has lifted from UNDER the surface mounted 49F6Y4K TL 1451A component. Unless someone familiair with this board can tell me there isn't supposed to be a connection going underneath the component? And it is not the copper trace but just a piece of the protecting layer that's ripped off? Holding to a strong lamp suggests there should be a copper trace however.

[michielvl]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

Hi there. I can't trash this board without trying to salvage it (besides that I am not able to find the replacement BenQ 48.L1A02.A00 ANYwhere on the net...).
So this is what I'm going to try, and maybe there's someone to help me with. See the attachment img: I need to make a connection (thinking about a piece of wire, is that a good idea anyway?), from A to one of the 5 marked in purple. But since the broken connection on the "A-side" is located under the TL1451A I do not know to which. Obviously I could desolder the TL1451A and see for myself. But since the copper traces are pretty weak I would rather choose not to.
So is there anyone:

1. with a schematic for this board so i can see where to connect to? I haven't found it in a full day google-searching; or
2. does anybody know out of his own experience where the "A" should connect to? It is the positive leg of C813.

Many thanks to anyone who could help me out because this L1955 is a way too good monitor to trash over this "small" fix!

[Krankshaft]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

Here is where to solder the jumper wire I traced it out with a continuity tester. I checked those five other traces radiating from under the IC as well and they had no tie to the torn trace.

This was a very bad trace to tear it's part of the PWMs startup circuit . Run a jumper wire between the two points and the trace is repaired.

Also be sure to check the 4 pin FETs the signaling transistors and the C5707s. A resolder of the inverter transformers pins and caps in between the C5707s should be done too and you will have a working monitor.

[Krankshaft]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

Oh sorry make that 2 jumpers one from the SMD cap to the through hole cap and from the through hole cap to the IC pin.

Use insulated stranded wire for the longer run to the IC.

An old clipped off component lead from new cap installation will suffice for the shorter run from the SMD cap to the through hole one.

[michielvl]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

Thanks so much for testing, this really helped me out! Tonight I will repair it and update here. This is really appreciated here on the other side of the Atlantic

[michielvl]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

Thanks againg Krankshaft, I am now posting from the L1955! Had to make one other "jumper wire" where the copper had cracked too. I know my soldering skills probably didn't help too much but oh, those cheap Taiwanese copper-saving schmucks... Anyways, it's running againg with all Panasonic FC's.

One remaining question regarding reliability: I noticed several people mentioning using a (extended) burn-in testmode. Could someone explain what this is?

[<danutzz>]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

Hey,
I have a problem with the same board on an L1955. It doesn't start at al. The front LED just flashes and it also makes a strange noise in the same time with the flashes. Do you have any ideeas of what could be the problem?
I am sorry for this silly post, I should have probably started reading more about LCD Monitor circuits since I have no ideea of what's inside, but I thought that someone might help me.
Thanks'

[PlainBill]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

Hey,
I have a problem with the same board on an L1955. It doesn't start at al. The front LED just flashes and it also makes a strange noise in the same time with the flashes. Do you have any ideeas of what could be the problem?
I am sorry for this silly post, I should have probably started reading more about LCD Monitor circuits since I have no ideea of what's inside, but I thought that someone might help me.
Thanks'

Classic symptoms of bad capacitors. Open it up, take pictures (see my signature for links) and attach them.

PlainBill

[<danutzz>]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

Thank you for your fast reply! I will open the case and post the pics on the forum today.

Daniel

Classic symptoms of bad capacitors. Open it up, take pictures (see my signature for links) and attach them.

PlainBill

[<danutzz>]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

I have just made a photo of the board. There is something strange in the left side of the image... Above the 1st and 3rd transformers the board is colored. It is not smoked, just colored. Any ideeas why?
I will try to find new capacitors and transistors and change them but I'm not quite sure when I will be able to do that since I will mostly be at school but I will post the result when the operation will be completed.

Daniel

[PlainBill]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

I have just made a photo of the board. There is something strange in the left side of the image... Above the 1st and 3rd transformers the board is colored. It is not smoked, just colored. Any ideeas why?
I will try to find new capacitors and transistors and change them but I'm not quite sure when I will be able to do that since I will mostly be at school but I will post the result when the operation will be completed.

Daniel

Heat.

Did you ever hear of the .jpg format for files? much more compact than .bmp.

PlainBill

[retiredcaps]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

You definitely have at least 3 bad capacitors. Replace them with high quality low ESR Panasonic FM or FR caps from digikey following PlainBill's instructions. Use FC if the other 2 are out of stock.

https://www.badcaps.net/forum/showthread.php?t=10419

Also for these Benq style boards,

1) you MUST resolder all the inverter transformer pins. MANDATORY.
2) check the c5707 transistors for shorts
3) check fu9024 fet for shorts
4) check the fuses to see if they are open (including the picofuse)

Some browning on the boards is normal due to heat.

[<danutzz>]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

Sorry for that... I was in a hurry and had to do print-screen from jpg imported in Word because the original img. was made with 12 mpx camera and couldn't upload it like that

Heat.

Did you ever hear of the .jpg format for files? much more compact than .bmp.

PlainBill

[<danutzz>]

Re: HP L1955 with Benq 48.L1A02.A00 inverter

I will do that as soon as I will have some free time
Thank you all for indications!
I will post results as soon as I will complete the tasks.

You definitely have at least 3 bad capacitors. Replace them with high quality low ESR Panasonic FM or FR caps from digikey following PlainBill's instructions. Use FC if the other 2 are out of stock.

https://www.badcaps.net/forum/showthread.php?t=10419

Also for these Benq style boards,

1) you MUST resolder all the inverter transformer pins. MANDATORY.
2) check the c5707 transistors for shorts
3) check fu9024 fet for shorts
4) check the fuses to see if they are open (including the picofuse)

Some browning on the boards is normal due to heat.