Dell 24” monitor E248WFPb DEAD (nothing at all!)

[iaino]

Hello there, this is the first time I have posted on this forum although I have successfully used other threads to repair monitors in the past, so a big thanks for that!

My problem now is that I have inherited a 24” Dell monitor which shows no signs of life at all, no power light, nothing and I'm a little stumped as to how to proceed. I have posted pictures of all the boards that are in the thing and I'll try to explain how far I've got poking around with my multimeter. I hope someone can help me fix this thing as it would be a shame to bin it cos it's massive!

All caps look ok visually but I know this isn't a sure sign of anything!
Nothing looks burnt or burst and nothing seems to get hot to the touch when power is on

When power is applied I get a reading of 290v at the other side of the fuse next to the power in connector so I guess the fuse is ok. The big cap gives a reading of 407v.
I get a reading of 23v from the caps on the inverter board.
When I try to get a voltage reading from anything on the wee board next to the main board or the video board I get 0v readings, as if the power isn't getting from the main power board to them.

I have tried powering it up with the inverter board disconnected and with the lcd itself disconnected with the same result- nothing.

Any thoughts?

[Bobdee]

Re: Dell 24” monitor E248WFPb DEAD (nothing at all!)

Hello Iaino
Have you checked the orange fuse F701 at connector to video board on power board

[iaino]

Re: Dell 24” monitor E248WFPb DEAD (nothing at all!)

Hi Bobdee,

Thanks for the quick reply! I hadn't checked it, I have now- it seems to be blown! I will replace it and post results.

Thanks again,

Iaino

[iaino]

Re: Dell 24” monitor E248WFPb DEAD (nothing at all!)

Ok, I replaced the fuse and plugged the monitor in. The fuse blew again straight away! Hmmm.... should I try a higher rating or is that just going to damage something else?

Help please!

[PlainBill]

Re: Dell 24” monitor E248WFPb DEAD (nothing at all!)

Ok, I replaced the fuse and plugged the monitor in. The fuse blew again straight away! Hmmm.... should I try a higher rating or is that just going to damage something else?

Help please!

Most likely it will just damage something else. You've got a multimeter, so trying to measure the voltage from ground to each side of F701 with power on. Then disconnect the power, wait at least 15 minutes and measure the resistance from ground to each side of F701.

PlainBill

[severach]

Re: Dell 24” monitor E248WFPb DEAD (nothing at all!)

Put your meter on a high AC scale and measure the wall outlet. 290v AC seems too high for any country. 240v AC would be better. Your input cap is rated at 450v but many input caps are rated for 400v which would be unsafe at this voltage.

This looks like a single output supply. 23v seems high but could be possible. It might be that the TDK inverter is a 24v design and they couldn't find a 24v/5v supply on short notice so they used a 24v only supply and added a 5v SMPS converter for the video board. Are the inverter caps with 23v and the 5v wee converter board input caps rated for more than 23v?

Provide some chip numbers on the 3 lead devices. On the power supply board IC702, IC603. There are two on the wee converter board and two on the video board. I'm looking for regulators that carry numbers like LM1117-25, 78M05, or BA033. Lots of video boards go bad because the regulators burn out. Regulators are cheap and easy to get.

You won't see anything with the video board disconnected because the video board commands the backlight on. Many monitors run the power led from the video board so it can display the various modes so no video board means no power led. The back light can be shorted on to verify power supply and inverter operation. BLON is a return line from the video board to the inverter and I see a single trace on the power supply board that does this. Unfortunately we don't know what the voltage limit on this wire is though if the TDK inverter is a 24v design then the input could be 24v safe.

I occasionally test fuses with the amp scale on the meter so I can see what the unreasonable current is. Don't leave the meter connected too long as the amp scale is essentially a short circuit.

The display, video board, or the power converter could blow F701. Disconnect all connectors including the wee converter board and reconnect one by one until the fuse blows.

[iaino]

Re: Dell 24” monitor E248WFPb DEAD (nothing at all!)

Ok PlainBill, here goes…

The voltage on the side of F701 nearest the power in connector is 28v. The voltage at the other side of F701 is 29v.

When I measure resistance I don't get any reading, i.e. the multimeter display just stays at “1” whatever ohms setting I try. (I'm not an expert but I have read the meters instructions!)

The cable next to F701 goes to the little circuit board that is pictured, which sits between the power board and video board.

[iaino]

Re: Dell 24” monitor E248WFPb DEAD (nothing at all!)

Hi severach,

I measured the wall outlet and it now reads 343v! ( I am in UK)

Caps on inverter board are 35v 220uf, wee board caps are same: 35v 220uf.

Chip numbers: IC702 is ‘KA 4310Z J28' IC603 is ‘MCR 100-6 828'

Hope this helps!

[iaino]

Re: Dell 24” monitor E248WFPb DEAD (nothing at all!)

Hi severach,

Sorry, to follow last post...

3 lead devices on wee board are both marked 'J598'
the ones on the video board are marked 'J231 950T65' on the small one and 'J243 G1084-18' on the bigger one.