Re: Dell 1901fp
What do you mean start-up caps? I'm assuming they are on the power board -- but which ones are they?
What do you mean start-up caps? I'm assuming they are on the power board -- but which ones are they?
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Re: Dell 1901fp
I said caps because you have two screens.
Should be one start cap per screen.
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Yes, in the SMPS section.
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[AFAIK]
Start-up caps cause the switching transistors in a SMPS to start switching.
Once they are switching the start cap doesn't do much.
They are usually something like a 22uF to 47uF cap near the transistors.
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The switching transistors are the two IC's with heatsinks [probably MOFETs] between the big cap and the transformers.
The start cap is probably one of the three caps roughly between them.
Can't be more specific without a schematic or tracing out the circuit.
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Someone who has seen more screens than I should take over from here.
.Last edited by PCBONEZ; 11-27-2011, 10:59 AM.Mann-Made Global Warming.
- We should be more concerned about the Intellectual Climate.
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Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.
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You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
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Re: Dell 1901fp
alright, that helps out some.
So is that cap basically for a soft turn-on? And by the way, Thank you!Comment
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Re: Dell 1901fp
In my mind it's more like a bump to kick-start a vibration.Mann-Made Global Warming.
- We should be more concerned about the Intellectual Climate.
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Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.
- Dr Seuss
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You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
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Re: Dell 1901fp
Yeah, I need someone that has played with more boards to give me an idea where to start attacking this. I can't find any schematics online, and I think there may be something not going right on the output connector. Should I for sure be getting 5.17 on 2 of the pins and 0's on the others? I know the ground pins should be 0, but the other ones are the ones I am not sure about.
Even if someone could point me in the direction of those caps you talk about, would help me. What is the voltage they should be at as the board is plugged in?Comment
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Re: Dell 1901fp
The power LED is controlled by the logic board.
I circled what I think are 2 voltage regulators.
1) Put your multimeter on 20 V DC if manual range.
2) Put your black probe on a ground screw (any one on the logic board will do fine).
3) Put your red probe on each voltage regulator pin EXCEPT the big fat tab.
4) Report the part number for each regulator.
5) Report all your findings like the following example,
U101 - part number AL1117-33 - pin 1 = 0.00 V, pin 2 = 3.3 V, pin 3 = 5.0 VAttached Files--- begin sig file ---
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Re: Dell 1901fp
And the power for the logic board and LED comes from the SMPS.......
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It's just not likely for identical failures to occur at the exact same time in two different screens.
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I think it's something in the SMPS start circuit that doesn't affect it once running.
The failures wouldn't have to -occur- at the same time but wouldn't be detected until the next power-up.
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That's my 2 cents.
Have fun.
.Mann-Made Global Warming.
- We should be more concerned about the Intellectual Climate.
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Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.
- Dr Seuss
-
You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
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Re: Dell 1901fp
Yes, I realize that, but since there is 5 V present on the connector pin, I want to see if that 5 V is making it to the logic board.
It is also likely that there should be something like 12 V DC to power the inverter section.
We all troubleshoot in different ways and I'm just suggesting test points if this were my monitor.--- begin sig file ---
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Re: Dell 1901fp
Okay, here are the measurements -- hopefully I explain this good enough......
1st regulator w/ metal flap (pins from left to right with flap on top)
part# FAN1537PAC
pin 1: 2.93v
pin 2: 0v (slowly climbs by a hundredth of a mV)
pin 3: 0.2mV
pin 4: 2.22V
pin 5: 1.79V
2nd regulator (from left to right with single pin on top)
part# AH3324985
pin 1: 0.3mV
pin 2: 0.3mV
pin 3: 10mV
top pin(4): 0.3mV
----HOPE THIS HELPS SOMEONE!! ----Comment
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Re: Dell 1901fp
According to the datasheet at
http://pdf1.alldatasheet.com/datashe...FAN1537PA.html
pin 1 = Vin should be 5 V
pin 2 = NC
pin 3 = GND
pin 4 = V1 should be 3.3 V
pin 5 = V2 either 2.5 V or 1.8 V
Let's verify that you are indeed getting 5 V on the connector on the logic board. So measure each pin on the logic board connector. At least one of them should be 5 V DC.--- begin sig file ---
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Re: Dell 1901fp
Just to double check, you want me to measure the voltages on the logic board pins from the bottom of the board, where the adapter connects from the the power supply board, right?
ps. I hope that made any sense. lolComment
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Re: Dell 1901fp
Okay, here's what I got.
on the 5.15v pins, they are both 2.85V.. the bri-out pin, is 2.15V.
I replaced the four larger caps on the board and none of them were bad. Someone earlier had mentioned the smaller caps by the big cap. but they don't seem to be bad either.Comment
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Re: Dell 1901fp
Okay, yesterday you reported that the blue and purple wires on the power board were measured at 5.18 V DC. Now, you are saying the same blue and purple wires on the logic board are now 2.85 V?
If yes, then something is wrong on the power board. Can you re-measure the blue and purple wires on the power board?--- begin sig file ---
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Re: Dell 1901fp
That is correct. When I didnt have the adapter connected, that's what I got.
With the adapter connected and pulling measurements directly off of the bottom of the logic board at the connector pins, I got roughly half of that. I will re-measure now and report back.Comment
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Re: Dell 1901fp
***UPDATE***
Both the blue and purple wires still have 5.18V at the harness that plugs into the logic board.Comment
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Re: Dell 1901fp
So I re-measured, and pin 5 which is furthest to the right with the tab on top, is giving me a reading of 0.09mVComment
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Re: Dell 1901fp
No need to apologize, I read that waaaay wrong. lol...
so here's the new readings.
Pin 1: 867mV
Pin 2: 0.3mV
Pin 3: 0.8mV
Pin 4: 0.3mV
Pin 5: 0.3mV
.... something seems really strange.Comment
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