Dell 3007wfp No Image

[budm]

Re: Dell 3007wfp No Image

The R132 (75k), D132, and the cap is part of the Snubber circuit to protect the MOSFET from damaging by the spike. You may want to check or replace the diode and the cap and verify if the resistor is still at 75 K).

[S. Bouchard]

Re: Dell 3007wfp No Image

Will check those and let you know the outcome.

Thanks for the help

[budm]

Re: Dell 3007wfp No Image

By the way, the Source resistor R133, Can you look under the board to see if it has a Diode connected in parallel with that resistor?

[S. Bouchard]

Re: Dell 3007wfp No Image

By the way, the Source resistor R133, Can you look under the board to see if it has a Diode connected in parallel with that resistor?

I don't see any Diode connected in parallel underneath but just in case, have a look.

[budm]

Re: Dell 3007wfp No Image

OK, just want to make sure, similar design will have a Zener Diode in parallel so the spkike voltage will not damage the current sensing circuit inside the SMPS IC, when the diode shorted out there will be very very current feedback to control the circuits, other person discovered that failure mode before due to squealing sound the power supply was making.

[S. Bouchard]

Re: Dell 3007wfp No Image

The R132 (75k), D132, and the cap is part of the Snubber circuit to protect the MOSFET from damaging by the spike. You may want to check or replace the diode and the cap and verify if the resistor is still at 75 K).

The cap you are referring to is the C132 (472K 500V) right next to R132 (Correct)?

R132 is 75K and its power rating 2 Watt?

[budm]

Re: Dell 3007wfp No Image

Yes, the Ceramic disc next to the 75K resistor, if it reads 75K within 5~10% then it is OK.

[S. Bouchard]

Re: Dell 3007wfp No Image

Yes, the Ceramic disc next to the 75K resistor, if it reads 75K within 5~10% then it is OK.

I just removed the resistor and it read 74.9K ... I removed the diode and it seems fine as well (450mv one way and Zero the other).

I removed the 2nd resistor (.36 ohm) and it reads .4 ohm but that's the accuracy of my meter (i believe).

I don't have anything to test that capacitor. If not this capacitor, what else, the MOSFET? How do I test that thing? Doesn't the issue have to be near this resistor (75K) which is making that high-pitch noise?

[budm]

Re: Dell 3007wfp No Image

I would try the cap since ceramic cap can vibrate, the question is it vibrating due the power supply is running at the wrong frequency or just that bad cap.

[S. Bouchard]

Re: Dell 3007wfp No Image

I would try the cap since ceramic cap can vibrate, the question is it vibrating due the power supply is running at the wrong frequency or just that bad cap.

I replaced that 472K 500v by a 472z 1kv (just to test) and the vibration / noise almost completely went away (without me touching anything). However, if I touch this new cap with the wooden stick, I can then hear the vibration and the noise. Is this vibration of this new cap related to the fact it has different tolerance % over the K part or is this indicative of the source of the vibration being something else?

[budm]

Re: Dell 3007wfp No Image

I do not think so, since the noise is less. Does the noise change with more or less brightness?

[S. Bouchard]

Re: Dell 3007wfp No Image

I do not think so, since the noise is less. Does the noise change with more or less brightness?

I have not re-assembled the monitor yet. This is with just A/C hooked up to the PSU board.

If that new cap is 472Z 1kv vs. 472K 500v and is half the size of the 472K is there any danger on leaving that one in or should I order a 472K 500v? The tolerances are pretty different on those two. -20% to 85% vs. 10% on the K.

[S. Bouchard]

Re: Dell 3007wfp No Image

I re-assembled the monitor and hooked it up to a PC via DVI and it is working.

In terms of the faint high-pitch noise, at low brightness I can barely hear it (if at all) but at full brightness, I can hear it a bit (with the power supply back in its metal shielding) the noise at high brightness is more like a small buzz.

So what do you think?

[budm]

Re: Dell 3007wfp No Image

I ran into buzzing noise that varies with the brightness setting, it turns out to be bad lamps. If you can live with it for now, the lamps will probably fail, then you can decide if you want to tear apart the panel to install new set of lamps or not.

[S. Bouchard]

Re: Dell 3007wfp No Image

Monitor has been on for over an hour. So far so good. The back casing is still off but I can't hear the sound anymore.

In terms of recap, I had a surface mount fuse on the controller board blown and I replaced all the caps on the PSU board with the exception of one (the replacement was too tall). I also replaced that ceramic cap but the replacement has different tolerances so I am not sure if that is ok (let me know on that Budm please)...

Otherwise, right now all looks good.

Thanks for the help and this great site.

[budm]

Re: Dell 3007wfp No Image

You are OK with that snubber cap, it does not to have to be precision.

[S. Bouchard]

Re: Dell 3007wfp No Image

Monitor worked fine for over 48 hours. About 30 minutes ago, while I was using it, a big electric zap (spark) sound occurred. After this sound, the monitor was still operational (image being displayed was all fine) but for obvious reasons, I unplugged it.

I took it apart again, and found the area where the spark / short occurred. It is right in the area of C132, R132 and R133. Something is definitely going on there.

Given my limited understanding of electronics, I have no idea what is causing this. R132, R133 all check out. D132 is fine as well. C132 was replaced but it is of different tolerance -20% to +85% vs original cap 10%.

Could it be that Mosfet K3265 (Toshiba part)? If so that part is obsolete so what would be a good replacement?

If not that, what else do you suspect could be wrong?

Added a third image showing where this Jump / Short occurred. You could see a slight part of the trace exposed.

[budm]

Re: Dell 3007wfp No Image

That looks like poor solder joints, the post of the heat sink is used for electrical connection, you should re-solder those two joints in the #3 pictures, use good soldering iron and flux.

[S. Bouchard]

Re: Dell 3007wfp No Image

That looks like poor solder joints, the post of the heat sink is used for electrical connection, you should re-solder those two joints in the #3 pictures, use good soldering iron and flux.

I'll redo the soldering on that post but neither of those visible in that image had been altered by me. That's original solder.

Looks like it current jumped from that post to the trace above it where a slight part of the trace was exposed.

Should I cover that exposed part of the trace above that post? If so what do you recommend I use?

What may have caused this?

[budm]

Re: Dell 3007wfp No Image

OK, on pictures 1, you have black rectangular showing the two pin line up, but the third picture, the two pins are offset so I am confused as to what I am seeing, The solder joint of the bottom connection (round pad) on picture #3 looks bad too me.