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Old 11-05-2013, 08:02 AM   #10
kalmara
New Member
 
Join Date: Oct 2013
City & State: Vratza
My Country: Bulgaria
Line Voltage: 240VAC 50Hz
I'm a: Hobbyist Tech
Posts: 3
Default Re: Dell 2007FPB teardown

Updates :
This morning I decided to go the trial & error way, since I don't have access to a scope. The first thing I did was swap the two PWM controller IC's in order to see will the problem power lines follow the IC's - I thought that the 3.3 and 12V will come up and the 5V will go down, but nothing actually changed. Conclusion - the problem is elsewhere.

And hour or so after that I found a resistor out of spec (think it was 4k7 or 47k, I forgot it already) under that white blob of dielectric-used-to-be stuff under the first PWM controller (upper right corner of my first pic), changed it and voila! The 3.3V rail came up, even without a zener.

Seems that the zener is going to be a 3.3V one, since it's cathode is directly on the 3.3V output (resp. anode on gnd), no current limiting resistors, no nothing. The PWM IC has it's resistor divider for the error amplifier input, just as those on the 5V and 12V lines, so I suppose something like thermal stability was in mind when they put that darn zener in there.
I decided not to search for the problem on the 12V line, since I don't have or plan on having dell speakers, so the hell with it.

Anyhow - now there's another problem. Without input signal the "NO VGA (or NO DVI-D) CABLE" message is absolutely perfect clear with perfect color and moving around the screen, but when VGA or DVI input is applied there is some sort of "picture", but it's quite noisy with white lines all over the place and it's jumping vertically. The other thing I noticed is when I left the monitor to display the "NO DVI-D CABLE" message for awhile, somethink like 10-15 minutes - after that it starts jumping vertically as well.

I ordered schottky diodes, zener diodes, some fuses and low ESR caps to beefen up the buck converter board and plan on changing ALL of the 10-22-47uF electrolytes in the digital board, and test again.
Meanwhile a friend of mine has prepared me an 2007WFP board, which is exactly the same as mine, with two differences :

First : The GPU is FLI5961-LF on my board, FLI5961H-LF on the widescreen board, which "H" suffix, according to some document I found on the internet means an "HDCP" (High-bandwith Digital Content Protection) feature on the DVI input of the GPU, so I suppose it'll work.

Second : the connector for the usb/buck board is on the opposite side of the pcb, but that can be redone in the matter of minutes. I think also swapping the FOUR (4) memory chips if i get to nowhere with my board and use his. Three are some atmel flash chips, and one is an 25x40 eprom.

Last edited by kalmara; 11-05-2013 at 08:04 AM..
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