low voltagw on 150uf 450v cap?

[capted]

Re: low voltagw on 150uf 450v cap?

budm, is the isolation diode dp801 on your schematic?? Now i'm thinking the mosfet might be faulty also because it is in the circuit also and maybe not giving the right voltage. Am I thinking right???

[budm]

Re: low voltagw on 150uf 450v cap?

DP801 is the isolation Diode which take the output of the bridge to charge up the main DC filter cap. If the MOSFET is shorted, it will blow the main AC fuse, if it is open or not operating, it will not cause low voltage on the filter cap, the MOSFET of the PFC circuit will not be running until it gets the PS_ON signal form the main board, and since you only have the power supply board running by itself, the PFC circuit is not on.

[ben7]

Re: low voltagw on 150uf 450v cap?

budm, is the isolation diode dp801 on your schematic?? Now i'm thinking the mosfet might be faulty also because it is in the circuit also and maybe not giving the right voltage. Am I thinking right???

Assuming that the 60v reading is on the capacitor, I think that the PFC diode could be bad.

Do you get resistance across the pins 1 and 4 of the PFC transformer?

How is DP801 doing? Does it test ok?

[budm]

Re: low voltagw on 150uf 450v cap?

There are two current paths for the output of the bridge to charge the cap, one is through DP801, another path is through the PFC INDUCTOR and DP802.

[capted]

Re: low voltagw on 150uf 450v cap?

diode check good. Thanks for clearing up the mosfet. Makes sense to me now! I do get resistance at the transformer. Next question I have is I did find a diode on the negative circuit side of the bridge that tests bad but it still is in circuit. I will test out when I get a chance. Do you guys think it is possible that the negative side could cause this problem?

[capted]

Re: low voltagw on 150uf 450v cap?

O.K. Now I'm baffled I plugged in the board again because I do remember getting 5 volts at the connector that is for the other board. Wanted to double check and post results. Well surprise I get 160volts now at the cap!!!! But than it starts dropping. I keep looking for something getting hot or loose. As I am doing this my gfi outlet pops!!! I reset it and as I am pushing the plug back into the board my meter reads 160v but when I move the plug a bit it drops again. When I get home I will desolder the 120v plug and check for cracks or something in that nature.. I will post my results later....UGH.

[ben7]

Re: low voltagw on 150uf 450v cap?

O.K. Now I'm baffled I plugged in the board again because I do remember getting 5 volts at the connector that is for the other board. Wanted to double check and post results. Well surprise I get 160volts now at the cap!!!! But than it starts dropping. I keep looking for something getting hot or loose. As I am doing this my gfi outlet pops!!! I reset it and as I am pushing the plug back into the board my meter reads 160v but when I move the plug a bit it drops again. When I get home I will desolder the 120v plug and check for cracks or something in that nature.. I will post my results later....UGH.

Did you put it back into the TV?

Have you replaced CP811 and CB806?

You likely touched something on the PSU which caused the GFCI to trip. Didn't feel any shock eh?

[budm]

Re: low voltagw on 150uf 450v cap?

I still think you have bad connections between the bridge and the cap.

[budm]

Re: low voltagw on 150uf 450v cap?

You only have 3 components to make 160VDC at the cap: the bridge rectifier, the isolation diode, and the cap. We know you are getting 120VAC at the Bridge AC inputs.

[capted]

Re: low voltagw on 150uf 450v cap?

Did you put it back into the TV?

Have you replaced CP811 and CB806?

You likely touched something on the PSU which caused the GFCI to trip. Didn't feel any shock eh?

No shock.... I think the gfi shut down because of me moving the plug and the ground was lost... I know the shock feeling trust me!!!! Ever hold an ignition wire on a car that was bad!!!! That will knock you down and test your heart at the same time... Ha

[capted]

Re: low voltagw on 150uf 450v cap?

Hey guys, if you look at this post, it is the same monitor. And I do have the same problem with that power regulator.. Also for some reason after I removed the 120v power plug and cleaned the holes-reinstalled I am now getting 160v dc at the cap and bridge...Go figure. The only thing I can think of is with the board on the bench I must have made the thru holes and solder loose when I was plugging in the board and unplugging with no support for the plug input.. https://www.badcaps.net/forum/showthread.php?t=13658

[capted]

Re: low voltagw on 150uf 450v cap?

Did some more playing. I connected the boards and checked the pins on the cable connecting them both. Where it is says grd I get ground and 5volts on the 5 volt pins. It seems that I am not getting any reading on the pin marked on/off when I press the power buttton. I checked the power reg's and they are all good(5.5v,3.3v) but the one that the other thread shows(the link I posted).. I think it has something to do with the usb ports. It is a 3.3v regulator. I am thinking there is a problem with the on /off signal from the logic board to the power board. At one point the led light up and the screen came on for a second than shut down(bulbs and screen are good) It would not restart although after a day unplugged it did the same thing again. Is there anyplace I can get a schematic for this model dell sp2008wfpt???

Thanks again.

[budm]

Re: low voltagw on 150uf 450v cap?

Is this the board you have?
http://www.shopjimmy.com/dell-683218...t-inverter.htm
Can you tell me the labels on that multi-pin connector and the voltage reading when it is plugged in but not turn on, then when it is turn on?
By the way, I never get to find out what the problem you are having with this monitor beside the 160V reading on the cap.
Your monitor seems to be the same as this one with burnt wires on the lamp assembly.
http://s807.photobucket.com/albums/y...%20SP2208WFPT/

[capted]

Re: low voltagw on 150uf 450v cap?

Is this the board you have?
http://www.shopjimmy.com/dell-683218...t-inverter.htm
Can you tell me the labels on that multi-pin connector and the voltage reading when it is plugged in but not turn on, then when it is turn on?
By the way, I never get to find out what the problem you are having with this monitor beside the 160V reading on the cap.
Your monitor seems to be the same as this one with burnt wires on the lamp assembly.
http://s807.photobucket.com/albums/y...%20SP2208WFPT/

Yup that's the one. I will give you the readings when I get to the board. I know I have 5 volts and grounds for the ones that are marked for it. The lamps did light up for a few seconds at one time. Keep in mind I can not give you readings when I power it on because it will not power on. The lamps are disconnecte dat this time so I don't think a shorted lamp could cause the problem..Will it power on without them connected?? At least the power button? The 60 volts at the cap was fixed when I removed the power input plug(120v) cleaned the holes and applied new solder... It was loose. The only thing I don't get is that I did read 120v at the bridge. Maybe the neutral or ground was missing at the plug? I used the ground screw and the hot leg on bridge to measure...

[budm]

Re: low voltagw on 150uf 450v cap?

OK, this board doe not have PFC Voltage booster circuits. I iwll wait for the readings and the pinouts. By the way, how did you verify that the lamps are good?
It explain why you are reading 60V since you are using the wrong ground when work in the primary side circuits, the neagtive leg of the 450v is your ground ref point for the primary circuit, not the chassis. The secondary side circuit ground is tied to the chassis. That was why I asked earlier to measure at the two legs of the cap.

[capted]

Re: low voltagw on 150uf 450v cap?

I got you. I thought I measured on the caps. I can swear I did but by that time my head was spinning..... The lamps came on for a few seconds when I first started playing with it. I changed all the caps on the power board (not the big one), put it together without the screen and the power light lit!!!! So I figured fixed. when I installed the screen it came on for a few seconds than went into the no power (power light went out also) Right back to square one after that!!!!!

[capted]

Re: low voltagw on 150uf 450v cap?

My head is going to explode!!!!! Was going to get the readings on the connector to post for you guys... I decided to try to turn it on before I pull the boards back out. I pulled one set of light connectors out and leave one connected(just wondering if the board needs to see a lamp or maybe the eprom has some type of fail safe) I'm sure you know what happend... Yup it is on now(blue power light but no back light) I don't want to touch anything yet. I pulled the two connectors that are next to each other, one blackand blue and pink and white... Is this for one bulb or just one end of both bulbs.

Thanks budm, you got me thinking about the bulbs.....

[budm]

Re: low voltagw on 150uf 450v cap?

The board has 4 lamps, there are detectors circuits in the inverter section. if the followings do not happen in the first 3 seconds, the inverter circuit will shutdown to protect itself.
When the inverter get to signal to turn on the backlights, if any one of the lamp is not connected, when the high voltage (1500~2000V) strike is applied to the lamps to fire up the lamps to get the ionizing going, the circuit will check and see if the lamp will draw current and if it will sustain the current draw or not, so if the lamp is not connected, then there will be no current draw, the circuit will shutdown, or if the current draw is too much, it will shutdown. If the lamps fire up and stay on, the voltage will drop down to running voltage of about 500~800V.
You should check the transformer high voltage winding resistance to see if one of the two transformer is bad, it can be bad MOSFET, lamp assembly.
You can learn more here:
https://www.badcaps.net/forum/showthread.php?t=10419
You can also make a couple of test lamps:
http://s807.photobucket.com/albums/y...g%20old%20CFL/

[capted]

Re: low voltagw on 150uf 450v cap?

The board has 4 lamps, there are detectors circuits in the inverter section. if the followings do not happen in the first 3 seconds, the inverter circuit will shutdown to protect itself.
When the inverter get to signal to turn on the backlights, if any one of the lamp is not connected, when the high voltage (1500~2000V) strike is applied to the lamps to fire up the lamps to get the ionizing going, the circuit will check and see if the lamp will draw current and if it will sustain the current draw or not, so if the lamp is not connected, then there will be no current draw, the circuit will shutdown, or if the current draw is too much, it will shutdown. If the lamps fire up and stay on, the voltage will drop down to running voltage of about 500~800V.
You should check the transformer high voltage winding resistance to see if one of the two transformer is bad, it can be bad MOSFET, lamp assembly.
You can learn more here:
https://www.badcaps.net/forum/showthread.php?t=10419
You can also make a couple of test lamps:
http://s807.photobucket.com/albums/y...g%20old%20CFL/

But would the power light still stay on when the lamp circuit shuts down? and does that mean each connector for the bulbs is for a single bulb(pink and blue is for one bulb)?

[budm]

Re: low voltagw on 150uf 450v cap?

The power light is driven by the logic board. There is no feedback signal from the inverter circuits to tell the main board if the inverter is working or not.
Yes, one pair of wires (White and Pink) per connector for 1 lamp. 4 connectors for four individual lamp.