Dell 1907FPc 2 seconds to black

[Mr Bill]

Dell 1907FPc 2 seconds to black.

I resoldered the 2 inverter transformers but it didn't help.

The capacitors appear to be united chemicon ky series (kxg for the big one).

Tested the fuses and they all check out ok

Tested the Q900 mosfet and i'm not getting anything under 30ohms.

Lastly i used a test monitor with a cracked screen but working ccfl's and i'm still getting 2 seconds to black.

Is there anything else to check?

Thanks
Bill

[retiredcaps]

Re: Dell 1907FPc 2 seconds to black

Is there anything else to check?

Measure the resistance of the secondary transformers. One is circled in red and other in yellow (pins 7 and 8). Report both measurements. If they are good, they should be within 3% of each other.

[retiredcaps]

Re: Dell 1907FPc 2 seconds to black

Tested the Q900 mosfet and i'm not getting anything under 30ohms.

Q900 is your power mosfet. If it wasn't working, you would not get any power.

The 2 mosfets in the inverter section are on the backside sandwiching the inverter pwm IC (Q801). Check those for shorts.

[Mr Bill]

Re: Dell 1907FPc 2 seconds to black

Q900 is your power mosfet. If it wasn't working, you would not get any power.

The 2 mosfets in the inverter section are on the backside sandwiching the inverter pwm IC (Q801). Check those for shorts.

The inverter transformers measure 444 Kohm on the one and 447 Kohm on the other.

Now the inverter pwm IC (Q801-Q803)
Q801 is being a bit funny. I'll get a reading with the red probe on say pin 1 and black on pin 2 but if i reverse the leads i'm getting 0L.

All the others i'm getting something in either K or M ohms no matter if i reverse the probes.

So would you suspect Q801?

[retiredcaps]

Re: Dell 1907FPc 2 seconds to black

The mosfets are circled in blue. The pwm IC is in yellow.

What is the part number of Q801?

[Mr Bill]

Re: Dell 1907FPc 2 seconds to black

The mosfets are circled in blue. The pwm IC is in yellow.

What is the part number of Q801?

The part # is ZC11. The 11 is written sideways.

Here are the readings for the mosfets circled in blue

1-1 0L
1-2 29.4 Kohm
1-3 0L
1-4 4.18 Mohm

2-1 0L
2-2 24.86 Mohm
2-3 0L
2-4 11.06 Mohm

3-1 0L
3-2 6.53 Mohm
3-3 0L
3-4 3.83 Mohm

4-1 0L
4-2 24.54 Kohm
4-3 0L
4-4 9.46 Mohm

And the other.....

1-1 0L
1-2 24.17 Kohm
1-3 0L
1-4 12.16 Mohm

2-1 0L
2-2 8.85 Mohm
2-3 0L
2-4 6.45 Mohm

3-1 0L
3-2 4.91 Mohm
3-3 0L
3-4 23.24 Kohm

4-1 0L
4-2 12.87 Mohm
4-3 0L
4-4 9.38 Mohm

[retiredcaps]

Re: Dell 1907FPc 2 seconds to black

The mosfets in blue might be 8 pin (hard to tell from the photo). Look at the part number and find its datasheet.

Here is how I measure multipin mosfets for shorts.

From

https://www.badcaps.net/forum/showpo...4&postcount=19

Some mosfets are more than 3 pins. To test those, identify the part number and search for its datasheet. Once you find the datasheet, the pins will be designated source (S), gate (G), and drain (D). It will probably be documented as S1, S2, G1, G2, D1, D2.

Simply test

a) black on pin S1- red on pin G1 - record ohms
b) black on pin S1- red on pin D1 - record ohms
c) black on pin G1- red on pin D1 - record ohms

Repeat for the "2" pins. That is S2-G2, S2-D2, G2-D2.

Note: a shorted mosfet would likely cause a very brief flash of the backlight or no backlight.

Here is a case study.

https://www.badcaps.net/forum/showthread.php?t=17659

[retiredcaps]

Re: Dell 1907FPc 2 seconds to black

The part # is ZC11. The 11 is written sideways.

Sorry, I meant IC801 (on the back). It looks like a 16 pin IC.

[retiredcaps]

Re: Dell 1907FPc 2 seconds to black

Lastly i used a test monitor with a cracked screen but working ccfl's and i'm still getting 2 seconds to black.

Describe how you did this test so we are on the same page.

[Mr Bill]

Re: Dell 1907FPc 2 seconds to black

Sorry, I meant IC801 (on the back). It looks like a 16 pin IC.

The IC801 numbers are:

0Z9938GN
A627R2 3G
0614B

the 2 mosfet numbers are:

9945N
AAF60

Here are my readings

S1-G1 17.37 M ohm
S1-D1 3.67 K ohm
G1-D1 0L

S2-G2 17.42 M ohm
S2-D2 1.077 K ohm
G2-D2 0L

And the other one:

S1-G1 17.35 M ohm
S1-D1 1.070 K ohm
G1-D1 0L

S2-G2 17.23 M ohm
S2-D2 1.061 K ohm
G2-D2 0L

[retiredcaps]

Re: Dell 1907FPc 2 seconds to black

Your mosfets are good.

[Mr Bill]

Re: Dell 1907FPc 2 seconds to black

Describe how you did this test so we are on the same page.

I removed the back from the broken screen monitor and plugged the ccfl's from that monitor into the power supply/inverter of the dell 1907FPc monitor.

[retiredcaps]

Re: Dell 1907FPc 2 seconds to black

I removed the back from the broken screen monitor and plugged the ccfl's from that monitor into the power supply/inverter of the dell 1907FPc monitor.

Humour me and try it as described in section #5 at

https://www.badcaps.net/forum/showpo...6&postcount=20

You don't have to remove the ccfls from the broken screen. Just stretch the connector to reach the Dell and don't let the two monitors touch (use cardboard or something).

[Mr Bill]

Re: Dell 1907FPc 2 seconds to black

Humour me and try it as described in section #5 at

https://www.badcaps.net/forum/showpo...6&postcount=20

You don't have to remove the ccfls from the broken screen. Just stretch the connector to reach the Dell and don't let the two monitors touch (use cardboard or something).

I'm getting a hiss on the one of the bulbs. I guess i'll be disassembling the screen

[retiredcaps]

Re: Dell 1907FPc 2 seconds to black

I'm getting a hiss on the one of the bulbs. I guess i'll be disassembling the screen

You might have a cracked ccfl.

Well, at least you might have spares. I was able to put a 4:3 ratio 19 inch ccfl entire assembly into a 16:9 19 inch monitor. It is obviously shorter, but it works ... until I broke a tab bond!

Now I get this nice black 1.5 inch stripe where the bond is unglued from the glass.

[Mr Bill]

Re: Dell 1907FPc 2 seconds to black

It was a bad tube but now i'm getting a white stripe at the one side. Auto adjusting the monitor did help a little bit. I rechecked the connectors but i'm not seeing any pins that are bent. The lvds connector to the screen is secure. Would a tab bond cause this issue. I don't think i damaged them but anything is possible.

[retiredcaps]

Re: Dell 1907FPc 2 seconds to black

Would a tab bond cause this issue. I don't think i damaged them but anything is possible.

Those tab bonds are very fragile. It is possible that 2 or 3 came unwelded from the glass which would explain the stripe. If I recall correctly, my stripe was black.