Dell 2408WFP broken power supply

[gunnish]

Got this one for free as broke, therefore i do not what did this do it. The monitor did not do anything on startup, I suspected bad caps as always. This was not the case. The power board is defect, the Power Factor corrector is blown and a diode is odd looking.

Basically: am i correct that the PFC is a L6561D (from these schematics https://www.badcaps.net/forum/attach...7&d=1359307560 in this thread https://www.badcaps.net/forum/showth...hlight=2408WFP However, the blown chip does not look like a ST to me.)

Which other components should i test?

Can someone confirm which chip it is?

[gunnish]

Re: Dell 2408WFP broken power supply

The diode is a IN5406. It conducts both ways and is physically cracked.

[bammbammfran]

Re: Dell 2408WFP broken power supply

you are going to need to also check the two diodes on that heatsink that is right next to those two parts to see if either one of them is shorted out in any direction. You should remove the bad diode and the 8pin 6561 before you check for shorts on those

I can not see what those parts are but one if probably a 3 pin and one might be a two pin
the 2sk3502 is probably one of the numbers of the two that I mentioned

[selldoor]

Re: Dell 2408WFP broken power supply

Basically: am i correct that the PFC is a L6561D (from these schematics https://www.badcaps.net/forum/attach...7&d=1359307560 in this thread https://www.badcaps.net/forum/showth...hlight=2408WFP However, the blown chip does not look like a ST to me.)

I think you read it wrong, if you look in the first post by Bicycle228 he has replied to retiredcaps questions to the original poster.
That is
2) IC601 is likely your SMPS chip.
a) What is the part number? = 1203P60

So he is saying IC601 is a 1203P60 Which is the NCP1200 series chip.

[stj]

Re: Dell 2408WFP broken power supply

1n5406 is a slow diode designed as a rectifier.
it's crap.

at a minimum i'd use a UF5408
much faster and a higher max voltage.

[gunnish]

Re: Dell 2408WFP broken power supply

I think you read it wrong, if you look in the first post by Bicycle228 he has replied to retiredcaps questions to the original poster.
That is
2) IC601 is likely your SMPS chip.
a) What is the part number? = 1203P60

So he is saying IC601 is a 1203P60 Which is the NCP1200 series chip.

Yes, there are two DIP-8 chips in this circuit and the 1203 is still there. The chip for the PFC is blown and as L6561D is a PFC chip, i assumed that this would be the blown chip.

1n5406 is a slow diode designed as a rectifier.
it's crap.

at a minimum i'd use a UF5408
much faster and a higher max voltage.

Isn't the diode in this circuit just supposed to be a rectifier? Because you are saying this I assume that is not the case. I assume that it is part of the PFC, what frequency does those normally operate at?

[bammbammfran]

Re: Dell 2408WFP broken power supply

your k3502 is almost definitely toast and that is probably what killed the diode and l6561.
Again, it may have taken out the other 2 leg diode on that heatsink. I would change all 4 and the fuse.
check the 4 leg bridge rectifier on the smaller heatsink on that end of the board for resistances from + to - once those parts are removed

[selldoor]

Re: Dell 2408WFP broken power supply

Yes, there are two DIP-8 chips in this circuit and the 1203 is still there. The chip for the PFC is blown and as L6561D is a PFC chip, i assumed that this would be the blown chip.

Yes I agree the L6561D is likely to be the blown chip as it is the only other
DIP- 8 chip on the board.

When I looked at your picture of it I read the IC number next to it as IC601 (sorry)
For future enquirers perhaps you can confirm what the IC number is, as it is not on the schematic

[gunnish]

Re: Dell 2408WFP broken power supply

Status report:

Rectifying bridge - OK
N_MOSFET K3502 - drain shorted to sources, charging gate does nothing, replaced with K2543
TO-220 diode - works
L6561D -replaced, now socketed
IN5406 - shorted, replaced

[stj]

Re: Dell 2408WFP broken power supply

Isn't the diode in this circuit just supposed to be a rectifier? Because you are saying this I assume that is not the case. I assume that it is part of the PFC, what frequency does those normally operate at?

they are both rectifiers,
but the 1n series is intended for rectifying slow stuff like AC psu's

the UF series is designed for high frequency stuff.
(UF = Ultra Fast)

[bammbammfran]

Re: Dell 2408WFP broken power supply

Status report:

Rectifying bridge - OK
N_MOSFET K3502 - drain shorted to sources, charging gate does nothing, replaced with K2543
TO-220 diode - works
L6561D -replaced, now socketed
IN5406 - shorted, replaced

AND ???? Still not working ??? OR ???
Can you post a good picture of the bottom of the board ?

[budm]

Re: Dell 2408WFP broken power supply

How about the Gate drive resistor (R668)/diode (D655) network, the Source resistor R670 (0.22 Ohm) are they OK? When the IC and the MOSFET blown up like that about anything in the path will be damaged.

[gunnish]

Re: Dell 2408WFP broken power supply

Tested now, the monitor does not react at all, not even the power button light.
I'll look at the resistors and diodes.

[jetadm123]

Re: Dell 2408WFP broken power supply

What the voltage at the main cap? Should be around 390vdc. If zero volts, check the main fuse.

[gunnish]

Re: Dell 2408WFP broken power supply

The main fuse conducts.
The primary electrolytic capacitor sits at 330 V.

Both D655 and R668 are surface mound and I'm not that good with desoldering and resoldering surface mount components, but as they are connected in parallel I seem to have to desolder them to measure them. Will do later.

R670 > 20 MOhm, so what will have to be replaced.

EDIT:
R670 now replaced.
The fuse blew when i connected the powersupply.

[budm]

Re: Dell 2408WFP broken power supply

R670 is the resistor for the Source pin of the MOSFET for PFC voltage booster circuit. So either the MOSFET is shorted or the Gate drive signal form the IC is stuck high instead of switching on and off at high frequency so need more troubleshooting.

[mustang80]

Re: Dell 2408WFP broken power supply

Hi all,
Sorry for posting to an old thread, but need advice relating to the same topic.

2 days ago, my Dell 2408 made a loud pop and is now unresponsive. I tried the main fuse first, obviously, with no luck. So I opened it. Took me a while to spot it as I was looking for blown capacitors. Then I spotted a blown resistor! It's number R670 on the board (22ohm).

My question is, is this something that is likely to just blow, or would a fault earlier in the circuit cause this? Happt to replace myself, but I'm just a bit unsure about finding the right value resistor.

If one of you could be very kind and point me in the right direction from this page:

http://cpc.farnell.com/webapp/wcs/st...&storeId=10180 I'd really apreciate it!

Here is a pic of the blown resistor:
[/URL][/IMG]

All help would be greatly appreciated, and my apologies if I broke any rules! First post.

Many thanks

[mustang80]

Re: Dell 2408WFP broken power supply

sorry, that should be 0.22ohm