HP L1955 with Benq 48.L1A02.A00 inverter

[bobbygg]

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

hi,rtech.i have just got in touch to see if supplier has the 8 leg mosfets or can get them,but i have just had a good look on his website and i dont think they do.but as board now works i will resolder transformers etc and hope for the best.
thanks for info.

[Rtech]

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

If one/both of your 8 legged Mosfets did fail, then that is normally all you would replace.So I assume this 'kit supplier' is not offering other parts which no doubt will be totally unecessary ??

[bobbygg]

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

hi budm,thanks for info.i am going to take board back out and solder around transformers etc.i have been in touch with supplier of kit and hopefully they will have right kit with the 8 legged mosfets.best to have a kit in case things go wrong.in the meantime thanks for all your help.regards

[budm]

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

Great, keep an eye on the board since they are browned in the output section which measn the oscillator may be running the wrong frequency due to bad tuning caps (gray rectangular caps by the transistors),or the DC filters are dying and letting through the AC ripple. See if the C5707/5706 are running hot. Also inspect all the solder joints, especially around the inverter transformers.

[bobbygg]

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

hi budm,thanks for getting back to me.thanks for showing me where fets are.
monitor was bought secondhand earlier this year,it worked when i tested it,then was put in storage.went to use it last week ,it would flash for split second then dark blank screen.when you cut power and switched back on same thing would happen.
but since i posted first message i had a look at the power supply socket and all 3 soldered joints had just broke away from board. i have resoldered joints ,plus on/off switch terminals and i now have test pattern on screen.
so problem was just soldered joint.
time will tell if any other problems crop up.
in the meantime thanks very much for your help.

[budm]

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

You have the wrong kit for your board version, the MOSFET in your kit has 3-pin MOSFET, your board uses 8-pin surface mounted MOSFET as you can see around the inverter section.
What is it not doing? What comes with the kit?

[bobbygg]

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

hi,budm,thanks for the quick reply.
please find enclosed 2 photos as requested.
i have a kit which includes 4xc5707,2x fu9024n,plus fuse.i have found where 4 xc5707 is located ,but not fu9024n,cant find them anywhere on board.
hope you can help.thanks

[budm]

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

@bobby, please post good clear pictures of your board, both sides.

[bobbygg]

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

hi,can you please tell me or show me with a photo where the 2 fu9024n fets are located,as i cant seem to find them on my board.thanks

[jakdedert]

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."

I know this is an old thread, but I just wanted to commend you Krankshaft, for going above and beyond. That was incredibly kind of you.

[donnsj]

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

I have the same monitor with the same inverter board (Benq 48.L1A02.A00). Which is toast. Monitor doesn't respond/turn on at all. Q812 was absolutely fried, and had actually lifted some of it's traces. So, I know so far I need to replace that part, 2 C5707s (shorted)(and i may replace all 4, just 'cause), resolder all 4 xformers (all 4 have cracked solder), and replace all the caps. Once that's done, check other parts around the damage, and see if there is any other questionable parts. Sheeesh.

The alternative is buying a whole replacement board(used) from one of the Hong Kong vendors on eBay, for about $30. Which is a crapshoot, in that it may need recapping anyway. And, maybe have to pay duty tax, etc. on top of that. not sure how that all works.

Does anyone have a soft version of the parts list/schematic for this board? I'd like to know where & what I'm probing. and what I need to buy for parts.

Thanks.

[retiredcaps]

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

I can hear some noise from the monitor (with almost constant frequency). Do you think that by replacing all the capacitors the noise will go away or is it another problem?

The smallest cap next to the SMPS plays an important role in the startup process and could be making that noise.

Thus, the earlier recommendation from forum members to replace ALL the capacitors.

edit: Reminder you MUST resolder all the inverter transformer pins (the 4 yellow boxes). MANDATORY.

[<danutzz>]

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

Good news... I have changed the 3 1000uF capacitors and resoldered all of the transformer pins and the result you can see in the attached image

I will also change the rest of capacitors but there is still one problem left: I can hear some noise from the monitor (with almost constant frequency). Do you think that by replacing all the capacitors the noise will go away or is it another problem?

Thanks,
Daniel

[PlainBill]

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

Another (free) one would be Irfanview. Been using that for almost a decade.
Just make sure you untick all the toolbar crap that it wants to install on the newer versions..

screenshot (of a screenshot )

Thanks for the suggestion. I'm looking into it.

And it certainly looks good. Sounds like it might be able to replace Paint for my purposes.

PlainBill

[Scenic]

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

Another (free) one would be Irfanview. Been using that for almost a decade.
Just make sure you untick all the toolbar crap that it wants to install on the newer versions..

screenshot (of a screenshot )

[<danutzz>]

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

Thank you for the hint, I didn't knew about this program . I have allready installed VuePrint and it works fine.

Daniel

Now THAT brings up an important issue. I've been using VuePrint for years for viewing and resizing pictures. It was quick and easy to use. Unfortunately it doesn't work properly under Win7 and is no longer supported.

PlainBill

[<danutzz>]

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

I'll also take that into consideration. Thanks'

I should have mentioned that you should replace ALL the electrolytic caps except the largest main filter cap. The main cap rarely, but not never, fails.

[PlainBill]

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

Now THAT brings up an important issue. I've been using VuePrint for years for viewing and resizing pictures. It was quick and easy to use. Unfortunately it doesn't work properly under Win7 and is no longer supported.

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.

I should have mentioned that you should replace ALL the electrolytic caps except the largest main filter cap. The main cap rarely, but not never, fails.

[<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.