HP L1740 Lcd inverter/power board

[George Ortiz]

Re: HP L1740 Lcd inverter/power board

All,
Strange problem with the my first inverter/power supply board. I re-capped it and installed into the monitor. Upon power up the Windows 7 logon screen shows for only about 10 seconds (green power led stays light constantly) and then goes out. I have a bright light on my desk and I can see the windows logon screen still. This is the same problem with this monitor and it's original inverter/power supply board. I removed this board and found only one blown cap. I took a another capacitor (same kind capxon) from another power supply board and then reinstalled the original board.
Turned it one and it does that same thing as the newly recapped power supply board.
Windows displays for about 10 seconds and goes out (the green power led is still lit).
I have reading other posts about other monitors, could this be a problem with the CCFL's??? Still new to troubleshooting these monitors. Thanks for all your help so far.
George

[George Ortiz]

Re: HP L1740 Lcd inverter/power board

PlainBill,
I checked on the other board that I have at home. This is my prototype repair board.
It has the same discoloration as the board I have here at work (the one photograhed here). There is another board with the same burn marks. All have blown caps.
Looks like running for extended time with failing caps. There are no circuit board tracks lifted on the other side of the boards.

[PlainBill]

Re: HP L1740 Lcd inverter/power board

Afraid not, sorry this board is new to me
Suggested a picture of back of board because it sounds like faulty inverter or CCFLs, and the dark heat area is probably the mosfets the members helping you will need to see the other side

Right, the discoloration is extreme, but could be nothing more than the result of running for an extended time with failing caps. Unless the traces have actually lifted from the substrate it is possible to replace any shorted transistors.

PlainBill

[Bobdee]

Re: HP L1740 Lcd inverter/power board

Bobdee,
would you happen to have any techincal information on this Philips inverter/power supply board or where I could get it. Real hard to find.
Thanks,
George

Afraid not, sorry this board is new to me
Suggested a picture of back of board because it sounds like faulty inverter or CCFLs, and the dark heat area is probably the mosfets the members helping you will need to see the other side

[George Ortiz]

Re: HP L1740 Lcd inverter/power board

Bobdee,
would you happen to have any techincal information on this Philips inverter/power supply board or where I could get it. Real hard to find.
Thanks,
George

[Bobdee]

Re: HP L1740 Lcd inverter/power board

All,
Finally was able to get a picture of one of the inverter/power supplies.
George

Just a suggestion
It seems that you may have a problems on the back of this board judging by those burn marks, (hope I am wrong)
Post a picture of the back of this board (without flash please if possible)
BTW Your board is a Philipps I believe and dmbj is a Benq, this monitor must use both boards
Bob

[George Ortiz]

Re: HP L1740 Lcd inverter/power board

All,
Finally was able to get a picture of one of the inverter/power supplies.
George

[George Ortiz]

Re: HP L1740 Lcd inverter/power board

thanks everybody for you input and help. I am going to order from digikey
enough capacitors to repair all four monitors and then have enough in hand to repair another two if they (most likely will) fail. Thanks again for your help!!!!!!!

[PCBONEZ]

Re: HP L1740 Lcd inverter/power board

I agree.

There is nothing -wrong- with using a higher volts caps, it's just that it makes things harder [fitting and on your wallet] and there aren't any benefits due to the higher voltage rating.

If you run a 50v cap in a 16v circuit the chemistry going on inside the cap changes the thickness of the oxide layer on the aluminum to be consistent with 16v.
[This is called reforming, as in reforming the oxide layer.]
That thickness is the primary characteristic the voltage rating is based on. When it adjusts to a thickness for 16v you no longer have a 50v cap, you have a 16v cap. If you then put the reformed to 16v cap into a 50v circuit the thinner oxide layer will allow excessive currents and overheat the cap most likely to the point of it failing quickly.

When you see an over rated cap [higher voltage than needed] the usual reason they did that is that higher voltage caps tend to be bigger [physically] and physically bigger caps [of some given grade] have lower ESR.
- They didn't go up in volts for the volts, they went up for the bigger can size.
It's the el'cheapo way to get better ESR.
The two ways usually used to get better ESR:
- Use a physically bigger cap. [The el'cheapo way]
- Use a better grade of cap.

You are much better off using a better grade than you are going to a higher voltage.
For screens Panasonic FM is an excellent choice.
In fact [for screens] Panasonic FC or Nichicon PW are better grades than what was originally in there maybe 80-90% of the time.
But if you can't find the specs for the old caps to be sure FC or PW are good enough replacements then defaulting up to Panasonic FM or better is the way to go.
Oddly, Panasonic FM is often less expensive than FC or PW.

.

[PlainBill]

Re: HP L1740 Lcd inverter/power board

Ok on the panasonic caps, but one question? Can I install caps that approximately double the voltage???? I have seen several lcd repairs on youtube and read about other repairs, that the replacement caps are double the voltage than the original caps.

You can, but I don't recommend it. Using higher voltage caps makes it more difficult to find replacements that will fit in the available space. Also, your higher voltage (and higher cost) cap will gradually reform itself to the lower voltage.

The original caps did not fail because the voltage was too high, they failed because the ESR (equivalent series resistance) rose as the cap aged. Eventually the capacitor overheated and popped it's top from the power it was dissipating. Panasonic FM series and similar low ESR caps from other reputable manufacturers have a much longer life expectancy.

PlainBill

[PCBONEZ]

Re: HP L1740 Lcd inverter/power board

The caps don't set or change the voltage, the circuit does.
The voltage marked on a cap is the caps limit.

If you have a piece of wire that's rated for [limited to] 250v can you safely use it on 120v?
- Same idea.
.

[George Ortiz]

Re: HP L1740 Lcd inverter/power board

Ok on the panasonic caps, but one question? Can I install caps that approximately double the voltage???? I have seen several lcd repairs on youtube and read about other repairs, that the replacement caps are double the voltage than the original caps.

[Toasty]

Re: HP L1740 Lcd inverter/power board

READ his FIRST post.

THEN go here:
http://www.mouser.com/ProductDetail/...vOCbYUtA%3d%3d

"Dimensions: 13 mm Dia. x 25 mm L"

I WAS working on this when you posted. AGE before BEAUTY....

[PlainBill]

Re: HP L1740 Lcd inverter/power board

Your first cap choice, the 470@50, is 13x25mm where the original is a 10x9mm. Can you go 25mm high?

I asked back in the beginning how high can you go...?

Toast

Note his 4:14 post. The original is 470 @ 25.

PlainBill

[Toasty]

Re: HP L1740 Lcd inverter/power board

Your first cap choice, the 470@50, is 13x25mm where the original is a 10x9mm. Can you go 25mm high?

I asked back in the beginning how high can you go...?

Toast

[PlainBill]

Re: HP L1740 Lcd inverter/power board

Your dimensions don't match the Capxon data sheet. If you are in the USA I suggest Digikey. All of the following match the Capxon dimensions and are in stock. They will ship the following order for under $3.00 via first class mail.

470uf 25V (3 each) P12388-ND Panasonic EEU-FM1E47 @ $.50 ea *
2200uf 10V (2 each) P12357-ND Panasonic EEU-FM1A222 @ $.76 ea
1000uf 25V (1 each) P12379-ND Panasonic EEU-FM1E102 @ $.76 ea
1000uf 10V (1 each) P12353-ND Panasonic EEU-FM1A102 @ $.50 ea
1000uf 6.3V (1 each) P12340-ND Panasonic EEU-FM0J102 @ $.37 ea

Unit quantity. There is about a 25% discount for quan. 10


PlainBill

[George Ortiz]

Re: HP L1740 Lcd inverter/power board

Toasty all caps are KF 105 C......

[Toasty]

Re: HP L1740 Lcd inverter/power board

Series is on the side opposite the values. Right near the temperature markings. Similar looking to this:

KF 105°C -or- KM(M) 105°C

KF & KM would be the series.

Toast

EDIT: Inverters are made by several. Usually marked on the board. FSP is one maker.

[George Ortiz]

Re: HP L1740 Lcd inverter/power board

All capacitors are CapXon:
470uf 25V 10mm x 9mm (3 each)
2200uf 10V 10mm x 12mm (2 each)
1000uf 25V 15mm x 12mm (1 each)
1000uf 10V 10mm x 9mm (1 each)
1000uf 6.3V 8mm x 9mm (1 each)

I think there is only 1 Transistor on here and checked for shorts, none found.
don't have digital camera right now so no pictures at the moment.
thanks.

Any recommendations on replacement caps would be very helpful.
I am going to order enough capacitors to repair the four inverter/power
boards. Also any info on who makes these invertors????

[Toasty]

Re: HP L1740 Lcd inverter/power board

Welcome George!

Original caps brand, series, & dimensions (DxH in mm), please. HOw many of each value? What is max height you can go?

Pics are always a plus!

I question a couple of the choices, but I'd need to see the originals info first. The PJ is a General Purpose cap and the ESR on a few looks a touch too high.

Also, resolder the transformers at all pins and check the C5707 transistors. Any heat damage or discoloration of the board around them would make them suspect.

Toast