Dell Monitor has "No Power"!!

[Tayninh55]

Re: Dell Monitor has "No Power"!!

Yes, It is a pain. I don't see how you guys can show the patience you do when helping people. Ok,,,,,,,,,the resistance between 1 & 2 is 11.0 ohms on the 200 meter scale. The resistance between 3 & 4 is 01.1 ohms on the 200 meter scale. Not sure if you wanted me to check anything else you had marked on the board or not. Do you still need another pic? What section of the board?

[budm]

Re: Dell Monitor has "No Power"!!

OK, #1 marking (LINE IN) is connected to the Thermistor (10 Ohms Thermistor?, you have to look) and line filters and then to the AC in (#2 marking) in of the bridge, the #3 marking (NEUTRAL IN) is connected to the Line filters and then to the Bridge AC in. So you should have 120VAC right at the AC1, AC2 pins of the bridge, verify that, then you should have 165VDC right at the two legs of the main filter cap, NOTES that, when you work int he primary side of the circuits, you cannot use chassis ground as the ground ref point for measuring DC voltage of the primary side of the circuit, the negative leg of the main filter cap is the DC ground ref point.

[Tayninh55]

Re: Dell Monitor has "No Power"!!

OK, I have 125V across ac1 & ac2.
I have 172V dc at both the caps

[bammbammfran]

Re: Dell Monitor has "No Power"!!

still no updated bottom picture ?

[Tayninh55]

Re: Dell Monitor has "No Power"!!

I don't understand what you want, bottom picture?

[bammbammfran]

Re: Dell Monitor has "No Power"!!

HI
I asked if you could post a new picture of the bottom of the power supply in post 39
I am trying to see what you soldered and if you might have possibly caused an arc of some kind somewhere that may have popped the fuse

[Tayninh55]

Re: Dell Monitor has "No Power"!!

Ok,,,,,I couldn't get a ceramic AC fuse in the right range, so I purchased a glass fuse and soldered wires on the end of the fuse, to attach to the board. It seems to work ok. On the other fuse, I just unsoldered the end towards the heat sink,,,,,,,,checked for voltages as you told me, finding none, I resoldered that end back into the board, as you told me. You can also see where I changed the two caps, they are now black, and the regulator. That is everything that I touched.

[bammbammfran]

Re: Dell Monitor has "No Power"!!

there is an arcing mark on that 16volt diode
Recheck that with the ohm meter from center pin to outer pin

Please clean the residue around your soldering
alchohol may work
lacquer thinner might work better.

did you use flux ??
or was you iron a weak one ??
I ask because the solder does not look like it flowed well

[Tayninh55]

Re: Dell Monitor has "No Power"!!

Yes,,,,,it is a weak iron. My old 40W played out on me and I sent my wife to Radio Shack to get a new one. I told her to tell them I didn't need a powerful iron, just one for printed circuit boards. She came back with a 15W and I used it and as you said, I had a hard time getting the solder to flow. Will get another one. The solder I was using was a Rosin Core "silver bearing" solder. Is that the diode on the big heat sink that you are talking about, if so, I have already checked it, and it seemed ok, but I'll check it again.

[bammbammfran]

Re: Dell Monitor has "No Power"!!

15 watts won't do much of anything
I am very surprised that you managed that voltage regulator with it or even with a 40watt
Even with flux core solder, adding external flux helps spread heat and helps the solder flow better, because the core is so minimal that it burns off too quickly.

Yes it is the one of the two that are on that large heatsink
It is the one that was giving you 16 volts and then jumped to like 30v

DO you see the dark spot on that diode between the center pin and outer pin ?
I am pretty sure that it sparked there and if this diode is shorted or close to it, it will stop all the power. I am not 100% sure that if you remove it, if the 5 volts will come on with it removed, but it might

[Tayninh55]

Re: Dell Monitor has "No Power"!!

I checked both diodes with the tester set on 200 ohms, the red lead on the center solder connection, then put the neg lead on each one of the outside solder connections, and the meter counted upwards on both diodes on the heat sink,,,,,,,,,,so I guess they are ok?

[bammbammfran]

Re: Dell Monitor has "No Power"!!

Normally when these short, they will stop the power supply on the high voltage side from turning on. Even though it is not completely shorted, it could be breaking down under load.This one may have arced and damaged a part on the power side instead of just shutting it down ?? the only way to maybe check would be to remove it and see if the 5 volts comes on or at least tries to come on.
You could try to see if a short jolt of power is showing up at that one or the 5 volt one when you first plug the power cord in
Having fun yet ??

[Tayninh55]

Re: Dell Monitor has "No Power"!!

Ok, I'll try that, but I'm going to wait until I get another iron. I sure don't understand how this could be "fun for you". You must be a glutton for punishment!

[Tayninh55]

Re: Dell Monitor has "No Power"!!

Bamm and others,,,,,,,,,,,,,,I'll be back,,,,,,,,just had to take a break to open the pool for the grand kids, do the garden, cut grass and all the other spring stuff. Will get back on it as soon as I can!