Dell E152FPg - 2 seconds to black

[smalltownguy]

Hi all,
Dell monitor as descibed, with '2 seconds to black' issue. Image is still there, CCFL's and screen tested on a sister montior with sucess, as well as the image board. The problems lies in the inverter board. I've already replaced all caps with a value of more than 10uf.

What next? Pics attached.

[alexanna]

Re: Dell E152FPg - 2 seconds to black

You could compare the resistance of the inverter transformers of the two monitors; the rule of thumb is 3% difference.
Fresh solder in the areas of the inverter transformers, sometimes can do wonders.

[alexanna]

Re: Dell E152FPg - 2 seconds to black

Also I don't know if it's just me,but I am unable to open up your photos.

[retiredcaps]

Re: Dell E152FPg - 2 seconds to black

You could compare the resistance of the inverter transformers of the two monitors;

It looks like pins 7 and 8 from the pictures which I can open.

[smalltownguy]

Re: Dell E152FPg - 2 seconds to black

Where are pins 7 and 8?

[retiredcaps]

Re: Dell E152FPg - 2 seconds to black

Where are pins 7 and 8?

See inverter transformers T2 and T3. Turn the board upside down and the pins 7 and 8 are marked on the solder side.

[smalltownguy]

Re: Dell E152FPg - 2 seconds to black

Desoldered and resoldered all the pins on both transformers. Problem persists. Next?

[retiredcaps]

Re: Dell E152FPg - 2 seconds to black

Next?

Still waiting for the resistance measurements as per post #2.

[smalltownguy]

Re: Dell E152FPg - 2 seconds to black

Resistance measurements:

Good Panel:

.584 kilohms
.578

Bad Panel:
.577
.565

Using the 3% rule of thumb, it would appear that the transformers on the bad panel are OK, correct?

[retiredcaps]

Re: Dell E152FPg - 2 seconds to black

Using the 3% rule of thumb, it would appear that the transformers on the bad panel are OK, correct?

Correct.

Have you replaced caps C106 and C107?

[smalltownguy]

Re: Dell E152FPg - 2 seconds to black

Have you replaced caps C106 and C107?

1uf 50v each? I have not yet replaced them.

I will go do that now, and report back.

Thanks,

STG

[smalltownguy]

Re: Dell E152FPg - 2 seconds to black

Replaced caps c106 and c107, no change.

FYI, I HATE the glue they used on these PCBs.

[alexanna]

Re: Dell E152FPg - 2 seconds to black

Do you have a CCFL that is not inside a panel?
What I am wondering is if each CCFL connector is able to light the CCFL.

[smalltownguy]

Re: Dell E152FPg - 2 seconds to black

Do you have a CCFL that is not inside a panel?
What I am wondering is if each CCFL connector is able to light the CCFL.

I've already swapped in a known working panel from a sister monitor. I also tested the panel from this bad monitor with anoither known good inverter, and it functions perfectly.

Edit: Also, the panel from the known working sister monitor behaves the same way with my bad inverter - on, then off.

Are you asking because you'd like to see if one of the CCFLs is not firing at all? I do have a spare CCFL for testing, but it goesn't have the proper plugs on the end. However, the CCFLs in my sister mointor are on 'tracks' and can be slid out for removal. I'll pull one out and try swapping it in place of each CCFL in my bad inverter and see if each socket fires the CCFL.

[smalltownguy]

Re: Dell E152FPg - 2 seconds to black

Okay, I've made a bit of progress here on the diagnosis. I pulled a spare CCFL from the sister monitor and found that it fired just fine in socket CN2 on my ailing inverter board, but it would not fire in socket CN3. So, I've narrowed down my issue to that half of the lighting circuit, anyway.

So what's next? Look at the transistors? I see 3 of them there in that half of the circuit: Q108, Q109, and Q110. I believe they're 2sd1616, based on the 'D1616 A' I see printed on them. I'll replace them if someone can point me to a suitable Digi-Key substitute.

[alexanna]

Re: Dell E152FPg - 2 seconds to black

did you have a lamp pluged into CN4 also?
Never mind i notice you only have 2 sockets.
See if there is any difference in the transistors on the other side

[smalltownguy]

Re: Dell E152FPg - 2 seconds to black

did you have a lamp pluged into CN4 also?
Never mind i notice you only have 2 sockets.
See if there is any difference in the transistors on the other side

I don't see a CN4 socket on this board. Did I miss something?

I had both of the sockets (CN3, CN2) on my inverter board populated with bulbs for my testing, if that's what you're asking.

[alexanna]

Re: Dell E152FPg - 2 seconds to black

no I thought you had 4 sockets for the CCFLs
Check the transistors for being shorted

[smalltownguy]

Re: Dell E152FPg - 2 seconds to black

no I thought you had 4 sockets for the CCFLs
Check the transistors for being shorted

Q110 shows a CE short. The other 2 transistors do not show shorts all 6 ways.

I will swap a transistor from my working board to see if that brings this inverter to life, unless one of the transistors in my stash will be a suitable replacement? I have some 2SA1015's or some C1815's - would either of those work?

-STG

[smalltownguy]

Re: Dell E152FPg - 2 seconds to black

I pulled Q110, and immediately I knew why it had a CE short - the transistor was smoked pretty good. It was tough to see since the side that blew out was facing towards the inductor L101. I replaced it with a 2sc1815 I had in my spare parts bin and test fired the monitor.

*poof*

Q1110 smoked again.

So, something else is wrong. Taking a close look, it appears that pins 3 and 4 on transformer T3 (same socket that wont light) have pins with solder that is dangerously close together. If those pins were bridged, could that be causing my problem? I see both pins share the same pad on the printed side of the PCB, so I'm inclined to say that it doesn't matter that they're bridged. Besides, I used my meter to test the same 2 pins on the other transformer (T2) and those pins show continuity. In fact, all four pins 2,3,4 and 5 all show continuity.

What's causing the transistor at Q110 to burn up?