Re: Dell 3008wfp PSU problem
I am having a lot of trouble tracing the rail back using the continuity method. Nothing seems to be connected. If the D22 has a voltage 17.59~17.77v does that mean it is on the 18v rail? Because the continuity beep is not present. I can only make it beep on 2 capacitors in fact.
Also does this flucation indicate the problem is further down the line towards the transformer? Or could the diode itself be causing a fluctuation? ~0.2v fluctuation is not as much as the ~1v difference seen at the pin itself.
Many thanks for any...
leapius
Senior Member
Last Activity: 02-10-2015, 01:10 PM
Joined: 08-20-2012
Location: bradford
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Last edited by leapius; 06-20-2013, 03:27 AM. -
Re: Dell 3008wfp PSU problem
I've not found one as of yet but could you give me an idea of how to do this myself? Also do you know what failing components are likely causes for voltage fluctations like this? Thanks....Leave a comment:
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Re: Dell 3008wfp PSU problem
Do you think the root of the problem is further back down the 18v rail somewhere? Could a schottky going bad affect the voltage like that?Leave a comment:
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Re: Dell 3008wfp PSU problem
Of the 5 diodes on the heatsink:
2 are at 25.2v constant
2 are at 5.17v constant
1 varies 17.77~17.58v (and dropping. This is the notorious D22 schottky - voltage seems to go slowly in the downward direction)
That was the only one close to 18v. As you can see it's not producing the same voltage as the output pin. Is that variance of interest?Last edited by leapius; 06-18-2013, 04:44 PM.Leave a comment:
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Re: 1 thin horizontal line across Laptop lcd screen
Could be delamintation of the ribbon cable to the panel. Try gently squeezing around the edges where the line goes to and see if that affects it at all.Leave a comment:
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Re: Dell 3008wfp PSU problem
I have now replaced the two capacitors (new Rubycons) that I found on the 18v rail and the voltage still fluctuates between 18.8~19.7 seemingly randomly but after a while it settles down. It tends to go high on cold start and then slowly drop back down.
What can I try next? Re-cap the whole board?Leave a comment:
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Re: Run LCD monitor with 2 CCFL out of 4
I have to agree with you about LED backlight debate. One advantage is better colour reproduction on CCFL. I did read about someone using a resistor in place of a bulb to provide the same load. You'd need to ask someone with more knowledge about specifics.
Simply ripping out your bulbs and inverter and putting in a strip of LEDs can be done but it's not so easy as the a/v board and psu won't like it and will likely just shut off.Leave a comment:
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Re: Hanns-G HG281D 'column shimmer' and start up problems
From the symptoms you describe I would suggest it is bad capacitors on the PSU causing this. Remember bad capacitors might not show any visual signs (indeed ones causing intermittent problems like this are more likely to be still working but on their way out). Your best bet is to test the voltages coming from each pin outputting from the PSU when it is on (be careful!) and reporting them here for the experts to see. But the black probe on a grounded screw and the red probe on each output pin and note the voltage. Take special...Last edited by leapius; 06-15-2013, 03:33 PM.Leave a comment:
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Re: Dell 3008wfp PSU problem
Thanks for the tip! Very useful - a cursory adventure around the board revealed 2 capacitors connected to that rail (a 35v next to it and a 25v further away in the middle). I will do some more thorough investigation tomorrow morning....Leave a comment:
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Re: Dell 3008wfp PSU problem
I get what you're saying. What tactic should I use to trace this 18v rail backwards and associated capacitors? I was trying to follow the trace visually but it becomes very difficult quickly. My limited knowledge about capacitors is that their purpose is to smooth voltage, so in seeing this fluctuation made me think that could be where the problem lies. My theory as to why the PSU is staying on but the screen goes blank was that it was sending fluctuating voltage to the a/v board and that it didn't like so shut down (and cascaded that to the tcon and...Last edited by leapius; 06-14-2013, 05:32 PM.Leave a comment:
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Re: Dell 3008wfp PSU problem
Pin | Good PSU | Bad PSU
P801 (to a/v board)
[LIST=1][*]5.15 | 5.11[*]5.14 | 5.11[*]5.14 | 5.11[*]5.14 | 5.11[*]5.14 | 5.11[*]0 | 0[*]0 | 0[*]0 | 0[*]0 | 0[*]0 | 0[*]18.18 | 19.1 > 19.65 > 19.18 > 19.71 > 19.21 > 18.8 > 19.18 > 18.86 (across about a minute)[*]0 | 0[/LIST]
P802 (to a/v board)[LIST=1][*]2.56 | 2.56[*]3.27 | 3.26[*]2.98 | 2.97[*]2.97 | 2.97[*]0 | 0[*]0 | 0[*]0 | 0[*]12.82 | 12.32[*]0 | 0[*]5.18 | 5.14[/LIST]
P803 (to inverter)[LIST=1][*]24.3 | 25.1[*]24.3 | 25.1[*]24.3...Last edited by leapius; 06-14-2013, 03:48 AM.Leave a comment:
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Re: Dell 3008wfp PSU problem
I have now re-tested the bad PSU as before and have found something I think might be interesting. Pin 11 on connector P801, which goes to the a/v board is acting weird. (see attachment for reference).
On the good PSU this stays a stable 18.18v and never fluctuates.
On the bad PSU I oberved it fluctuating (over about a minute) when I turned it on in the following sequence:
19.11v
19.65v
19.18v
19.71v
19.21v
18.8v
19.18v
18.86v
At that point it...Leave a comment:
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Re: Dell 3008wfp PSU problem
Ok, I again moved the bad PSU back to the monitor with the broken panel. This time it went blank with renewed regularity (virtually every minute or so at the moment).
From this I think we can assume it is indeed the PSU that is at fault as the symptoms are confirmed to have moved to the other panel when the PSU is swapped in isolation (knowing that all the other boards on the broken panel monitor are working). The question now is how to test the voltages once I know the screen has gone 'blank'.. There is no way to know if I unplug the...Last edited by leapius; 06-13-2013, 10:11 AM.Leave a comment:
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Re: Dell 3008wfp PSU problem
Quick update: I turned it off and put the fans on. Turned it on again about 90 minutes later after it was completely cold. Went blank after ~5 mins. Turned it off/on, went blank again after ~3 minutes. Off/on again - currently still on (for about 2 hours so far). Kept the fans on this time and as before, the blue LED always stays on but the blank events occur at seemingly random intervals.
I'd love to test the PSU when it is in this 'blank' state (without power cycling it) so I can see if the voltages are different but it's inaccesible...Last edited by leapius; 06-13-2013, 08:03 AM.Leave a comment:
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Re: Dell 3008wfp PSU problem
Well I seem to be falling down the rabbit hole here. I think I should point out that the good PSU comes from a 3008 that works normally but has a cracked screen (which I have temporarily).
I tested both PSUs last night and they both gave the same voltages on each pin of the three outputs. So I thought maybe I should heat the bad PSU up and put it under more load so I connected it to the cracked panel and left it powered on for about 40 minutes (partial picture obviously).
Came back and at this point it was too hot to touch...Last edited by leapius; 06-13-2013, 03:53 AM.Leave a comment:
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Re: Dell 3008wfp PSU problem
Lumberjack, thanks loads for the detailed explanation - very helpful. I thought you'd need the inverter and tcon plugged in for the psu to stay on you see.
I will get the readings done in a few hours when I get home from work and post my findings.
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Re: Dell 3008wfp PSU problem
Ok got it, do the boards have to be screwed to the metal casing to earth them? I ask this because the only way to get to the psu is by flipping it (and the a/v board) over but then I can't connect the tcon and inverter to it and the psu wouldn't turn on as a result. It would be easier to remove the metal cover so I can get to the points and leave the psu and av board in the same orientation. I guess I would need some sort of insulator to protect the underside of the board from contacting the metal of the panel, would anti-static bags work?
...Leave a comment:
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Re: Dell 3008wfp PSU problem
Thanks, I will do this tomorrow and get back to you. When you say 'pin 1 says..' how do I know what it should be? By the wire colour? Or do you mean what the good PSU says and then what the bad PSU says on the same pin? There are three output blocks to check....Leave a comment:
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Re: Dell 3008wfp PSU problem
Hi guys, sorry for the late reply, I'm actually late for work right now so don't have time to post closer photos of those diodes but I looked with my jewelers loop and they seemed ok (no gap) possibly the light angle on that photograph. I do like the dry joint theory as this PSU does heat up a lot.
If you can tell me what outputs to check I can give you readings from both PSUs for comparison when I get back from work. There does seems to be a lot of that residue and I do actually have some isopropanol in stock so I'll clean it up as suggested...Last edited by leapius; 06-11-2013, 03:05 AM.Leave a comment:
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Re: Dell 3008wfp PSU problem
Thanks for the quick repsonse lumberjack. You must have eagle eyes to spot that! I will reflow those joints tomorrow and get back to you with results. They seemed ok to me but I am no expert. A lot of the joints seem a bit dull and I am aware this PSU gets red hot. I can take closer photos of particular part of the board if you'd like? I have access to the good PSU and can run tests with it as required.
Many thanks.Leave a comment:
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