Re: Dell 2407WFPb Monitor - Bad Cap
I managed to fix mine as well.
I thought it wasn't fixed when I first tested it, because C605 only had rectified mains on it, not the ~400V DC expected if the PFC is boosting the voltage. But it turns out the PFC circuit doesn't turn on until it's connected to the other board, this is the signal "Power_off" which controls the optocoupler IC652.
I ordered all the parts from LCSC, but I'm sure Digikey/Mouser would have them too. There were some parts which aren't available anymore so I had to find...
sean0118
Senior Member
Last Activity: 11-30-2023, 11:46 PM
Joined: 06-03-2016
Location: Sydney NSW
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Re: Dell 2407WFPb Monitor - Bad Cap
Ah, never mind, I was wrong.
R666 (24.9K) gets put in parallel with R674. Which does make it regulate to 391V DC as would be expected.
So the design looks ok, the cap is just bad quality.Leave a comment:
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Re: Dell 2407WFPb Monitor - Bad Cap
Thanks, the circuit diagram is really helpful.
I think there's actually a design issue. The feedback resistors for the boost circuit are 499k+232k+232k and 8.25k. The L6561 has a reference voltage of 2.5V. This will cause it to try to regulate to +294V DC.
2.5V *971.25/8.25 = 294V
But if you rectify 230V AC you get 325V DC, which is the input to this boost converter (and 30V higher than its output set point). Shouldn't the output be set to regulate at +400V DC? Or at least 350V?
...Last edited by sean0118; 08-03-2019, 09:43 AM.Leave a comment:
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Re: Samsung Main Board - BN41-01800B
Good news, I removed the Realtek RTL8201F chip, the short is gone, now about 400ohms from the 3.3V rail to GND.
400 ohms seems a little low, but maybe it's normal, will put a new chip on and see what happens.
edit: That Realtek chip was horrible to remove, lead free solder and a centre gnd pad.
Last edited by sean0118; 05-07-2019, 05:23 AM.Leave a comment:
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Re: Samsung Main Board - BN41-01800B
Ops I was misunderstanding the datasheet. The regulator is pin code A: GOI.
The short is on pin 3, so actually it's input rail, not the 1.8V output.
I did make some progress though, there's a Realtek RTL8201F ethernet driver which heats up about 5C above everything else. Turns out it's 3.3V inputs are shorted to GND. I guess the 1.8V regulator is powered from the 3.3V too.Leave a comment:
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Re: Samsung Main Board - BN41-01800B
I thought 2A would be heaps too, but I left it on for ~ 1 minute and nothing heated up at all.
There's definitely a short somewhere on the rail. The lab supply goes into constant current mode and limits to 2A. The voltage is about 0.3V measured on the Samsung board. So ~0.15ohm, all the other regulator outputs are in the megaohm range.
"The LD1117AG can only supply about 800 miliamps, are you sure you have a short? , Does the input voltage to the regulator ic drop when the tv is turend on? If there was a...Last edited by sean0118; 04-28-2019, 12:54 AM.Leave a comment:
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Re: Samsung LE40C750R2K capacitor on PSU blew up when unplugging inverter board
The output of the power supply probably has high inductance, once you remove the load the current through the inductor will continue to flow causing the voltage to rise sharply.
Some power supplies, like flybacks in CRT TVs use this to generate very high voltages.
But in your case the voltage got high enough that it found a path through that capacitor.
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Re: Samsung Main Board - BN41-01800B
How much current would you expect to need?
My lab supply only goes up to 2A, nothing heats up at all.Leave a comment:
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Re: Samsung Main Board - BN41-01800B
Seems like a decent idea, I'll give it a go....
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Samsung Main Board - BN41-01800B
Hi everyone,
I'm fixing a Samsung TV which was apparently damaged by lightening (along with a PS3 plugged into it). I don't have the tv here and I've forgotten the model number.
But anyway, the power supply board was shutting down due to over current protection. But runs fine with everything unplugged.
The main board (Echo P Unique BN41-01800B) has a short to ground on the output of the 1.8V regulator IC201 (UTC LD1117AG 18A01PDS6). Anyone have a schematic for this board?
I can't see any obvious damage, but there's a large... -
Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge
Thanks Angelos, I think you might be right and that my problem is the panel.
I found quite a few documents from LG saying that the firmware update and different voltages are required to fix it. But none of the documents I have list the new voltages.
I decided updating the firmware was too much work, even though it might be possible with a generic programmer.
In the end I set my voltages to those in the 'Quick Reference Alignment Hand Book' (Va = 65V, Vs = 188V, -Vy = -75V, Vsc = 115V,...Last edited by sean0118; 02-09-2019, 07:07 PM.Leave a comment:
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Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge
Are these oscillations normal for plasmas? I can see them on both the YSUS and ZSUS waveforms.
edit: Uploaded second image, yellow is YSUS, blue is ZSUS....Last edited by sean0118; 02-04-2019, 02:39 AM.Leave a comment:
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Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge
Nvm it's a 15V rail and the best place to measure it is B21 at the bottom of the Z-sus. Mine was ~15.2V so seems fine.
I'm out of ideas again. I guess it could be the panel, but seem strange that it gets worse the longer its on.
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Re: Samsung LN40A550P3F 40" HDTV, slow to turn on
Yes, lead-free solder has a high melting point, but if you add leaded solder it will melt easier.
Then use two soldering irons, one either side to lift it off. Once it's removed use solder wick to remove all the existing solder. Then solder the new capacitor on, one pad at a time.
edit: Post a pic of the main board as it is now, with the new capacitor.
Might also be worth trying your original power supply board? In case the Shopjimmy one from your first post is fau...Last edited by sean0118; 02-02-2019, 12:25 AM.Leave a comment:
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Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge
I replaced all the Samwha RD capacitors (10uF, 350V) on both the y-sus and z-sus. But can't see any change.
One thing I did notice is the maldischarge gets worse the longer its left on. I tried to reproduce it with a heat gun but couldn't. But If I leave it on a white screen for ~15min it gets quite bad once I switch back to a normal image.
Does this model of LG have an 18V rail for the IPMs? Where is it best to measure it?Leave a comment:
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Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge
It was worth a try, but lowering Vs didn't improve it. I think I might have gotten it a bit better with some small adjustments to set_up and set_down. But it's still maldischarging.
I ordered some replacement capacitors, I'm not too hopeful but curious to see if it helps.Leave a comment:
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Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge
Thanks, I haven't tried lowering Vs that much, I'll give it a go.
I'll try to adjust setup/setdown some more too.Leave a comment:
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Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge
I reduced set_down a bit so the down ramp is 100uS. The quick reference book (attached) had some waveforms which were clearer than the manual.
I also tried varying set_up and set_down as well as Vs. Did see some changes, but didn't fix it. If I decrease set_up a lot I get dark sparkles instead of bright ones.
Anyway, I noticed there's 3-4 Samwha RD capacitors (10uF, 350V) on the Y-sus which heatup a lot. Some are over 45C, hotter than everything else on the board, including the larger...Last edited by sean0118; 01-19-2019, 09:57 PM.Leave a comment:
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Re: LG PDP42V7 / Palsonic PDP4275 Plasma - Maldischarge
oh, yes I should have mentioned, I have tweaked set_up and set_down to try and get the y-sus to match the waveform in the manual.
set_down is longer than it should be, it's something like 120us instead of 100us. But if I reduce set_down it just makes the ramp reach -Vy earlier then it stays flat at -Vy, it doesn't go back up to 0V earlier. Does that make sense? Otherwise I'll save a scope image of it.
edit: What sort of programmer is used to update the firmware? I saw this mentioned in another...Last edited by sean0118; 01-19-2019, 07:26 PM.Leave a comment:
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Re: I think i killed it Toshiba 40L1333DB
Oh nice, let us know how you go.
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