Re: Dell 2408WFPb display inoperative
Well I didn't find anything obvious under the magnifier. I guess next I'll try and trace that pin on the logic board. Unfortunately one of my cars died so I'll be spending Christmas rebuilding the cylinder head. Yay!
magorkonig
Member
Last Activity: 01-17-2017, 12:15 AM
Joined: 11-19-2016
Location: Oakley, CA
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Re: Dell 2408WFPb display inoperative
Sure enough, with a 3V batt on pins 1 and 9 of CN701 with it disconnected from the logic board got the PFC to come alive. I had 401VDC across large cap C605. Pulling logic board now to check under magnifier. Will update with any findings.Leave a comment:
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Re: Dell 2408WFPb display inoperative
So the 2.8V i am reading in CN701 pin 3 (by the diagram) is not feeding R677. Pin 9 is the one feeding R677 and it is 0V.
stj: I have not replaced any parts yet.
budm: Resistance between Vcc and Gnd on the PFC IC is OL. I think we are on to something with the lack of voltage to pin 9 on CN701 to feed Q656 and so on. I have looked all over the power and logic boards to find Q504 and Q505 and have been unable to find them.Leave a comment:
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Re: Dell 2408WFPb display inoperative
Checked Q654 for shorts to ground on the base, emitter and collector. None were found. Continuity to surrounding components per the schematic were also ok. I will check the solder joints tonight and see if I can come up with something. By the diagram it looks like IC652 controls Q654 so I'll be sure to check the joints on that one.Leave a comment:
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Re: Dell 2408WFPb display inoperative
Thanks for the schematic jetadm123. I checked the Vcc voltage per the diagram and when I measured pin 8 (Vcc) with the black probe on ground for the board I got -77.18VDC. When I checked the voltage using the IC ground pin (#6) it came up as 0.517VDC. I guess I need to know which is the correct way to read the voltage on Vcc line and depending on the answer I can assess my results. I will get out my magnifier and check all the solder joints again.Leave a comment:
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Re: Dell 2408WFPb display inoperative
So from I have read the standby voltage across C605 should be ~1.4 x input (120VAC) which is what it is. But as you state above, when operational it should be 400VDC. Given that not all the wires in connector CN701 have 24 volts could it be because C605 is not getting the stepped up voltage? And since the beginning as soon as you plug the monitor in the front power light is a solid amber color and doesn't change. Maybe something is preventing the power supply from coming out of standby mode. I'm just throwing out ideas. Please forgive my lack...Leave a comment:
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Re: Dell 2408WFPb display inoperative
So the whole family has been sick so it's been a while since I have worked on the monitor. I read through both posts you listed and interestingly enough when I plugged it in to do more testing following those posts it powered on. I though maybe all the disconnecting and reconnecting things may have resolved it. I put it back together and went to install it in the house and it was back to the failed state again. So it's back apart on my bench and all the previous readings I listed are the same.Leave a comment:
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Re: Dell 2408WFPb display inoperative
I have included the requested photo. I don't see anything mounted on the board on the left side of the fuse and the other side according to the etching looks like it's connected to a couple of caps (the large one above it and the tiny one beside it). The readings to ground are left side= 1.3kohms and right side= 4.8kohms. Maybe there is no voltage to that fuse because it isn't used??...Leave a comment:
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Dell 2408WFPb display inoperative
Greetings all,
The problem: blackout happened at the house and now monitor when plugged in will give a green power button for a second and then go to yellow. Power button does not function and there is no display using any input source. Using the great information I have found on this forum I have obtained the following test results:
Power board A
118.9VAC both sides of F601
118.7VAC into CN603
Power board B
23.4VDC both sides of F701
159.6Volts across large cap C605
Vcc pin on IC601 is 14.8VDC
D602 reads OL... -
Re: New Members - please post your introductions here
Found this forum from a post relating to a specific problem I am having but I am looking forward to learning all there is to offer. I have moderate technical ability mostly with automotive DC systems. I hope to start saving my components instead of throwing them away!Leave a comment:
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