Dell monitor

[cb92]

This unit is ten years old, just for practice. I have ac and dc on the ac side of the smps. Nothing on the load side of the smps. There seems to be an optoisolator in the circuit. Is the smps bad or is it not getting turned on?

I hope the schematic comes through, I've been trying all day to downsize it.

[amilacellular]

Re: Dell monitor

thsnks dear..

[momaka]

Re: Dell monitor

Check voltage on the start-up capacitor for the SMPS controller. (It's usually a small 10/22/ or 47uF cap on the primary side of the PSU). Use hot ground (the negative side of the big capacitor on the primary) as a reference. BE CAREFUL! There are high-voltages on the primary side.

Unfortunately with that schematic, I can't help you more than that. Try using a different software to resize your pictures, like GIMP or Paint.NET. Have a look on Download.com. There's a ton of programs that can resize/edit/convert images better than Paint. Save in JPEG format.

[cb92]

Re: Dell monitor

Thanks a lot, Momaka. I think I see the cap you mention on the schematic. I got Paint.net, will see if it helps, changed the pic to jpeg, will re-post just to see if it's any better.

[Scenic]

Re: Dell monitor

just upload the .pdf (?!)

[momaka]

Re: Dell monitor

I think I see the cap you mention on the schematic.

I think I see it too now. Looks like C907 if I'm not mistaken. It's 47uF, 50v. If you follow pin 4 of the main transformers (using the service manual as a reference), you should first encounter a diode and then a 10 Ohm resistor. Check those to see if they are good - if they are, power on the monitor and measure the voltage across that 47uF, 50v cap with respect to hot ground. Note what the voltage is.

Also, post what the PWM controller is (IC901 if I'm reading that right) - i.e. post the part number. I can see it's ICE-something but that's about it.

[cb92]

Re: Dell monitor

I got 165 volts DC across the cap,(same reading on either leg to the + on the rectifier) and the diode and resistor read ok on the board. The IC is ICE2a501. I removed the optoisolator and checked it, it didn't seem to test as 'ok'. I put on a used one, but no changes. I'm going to pick up some new optoisolators, ones I take off junk don't test as 'good'. Do they fail often? I'm looking for the most likely suspects in power supply repair.

And interesting side is that this monitor wants 5 volt and 12 volt. For a shop monitor, I'm considering finding a computer power supply and using it to power the monitor.

Another funny thing...I was putting in a screw, the monitor was not flat level on the bench, and it made a hissing sound as I put pressure on the unit to tighten the screw....is the flat screen under vacuum? I did not puncture anything with a screw, but I may have cracked something...

[momaka]

Re: Dell monitor

I got 165 volts DC across the cap,(same reading on either leg to the + on the rectifier) and the diode and resistor read ok on the board.

Hot ground is NOT the "+" side of the rectifier, it's the "-" side. Recheck the voltage again.

The IC is ICE2a501.

I don't know if I'm having a bad day in regards to finding data sheets, but this is the second one I can't find. If anyone else finds it, post a link here. Would be useful to have it so that we can check if the voltage on that 47uF, 50V cap is high enough to start the controller.

I removed the optoisolator and checked it, it didn't seem to test as 'ok'. I put on a used one, but no changes. I'm going to pick up some new optoisolators, ones I take off junk don't test as 'good'. Do they fail often?

Optoisolators do fail, but very rarely. How are you testing them exactly?

And interesting side is that this monitor wants 5 volt and 12 volt. For a shop monitor, I'm considering finding a computer power supply and using it to power the monitor.

That should work fine.

Another funny thing...I was putting in a screw, the monitor was not flat level on the bench, and it made a hissing sound as I put pressure on the unit to tighten the screw....is the flat screen under vacuum? I did not puncture anything with a screw, but I may have cracked something...

Nope, the the screen is not under vacuum. However, the 2nd or 3rd outermost layer is the thin film transistor (TFT) matrix sheet, and that can crack (since it is like glass). The hissing you heard may have been just the screw making weird noises.

[retiredcaps]

Re: Dell monitor

This process would go a lot EASIER if the OP told us what the Dell model number is and provide clear focused top down view pictures of the monitor following the instructions in my sig file below.

[retiredcaps]

Re: Dell monitor

If anyone else finds it, post a link here. Would be useful to have it so that we can check if the voltage on that 47uF, 50V cap is high enough to start the controller.

13.5V according to (ICE2AS01). "S" not "5".

http://pdf1.alldatasheet.com/datashe.../ICE2AS01.html

[cb92]

Re: Dell monitor

The monitor is a Dell 1800FP. The Koreans sold this monitor to a lot of companies, from what I see. The 47uf cap #c907 is directly connected to the negative (-) leg of the rectifier. The solder track from it goes to the transformer and the (-) symbol on the board. Funny thing, the solder track has a gap right at the cap, but testing shows continuity through the track under it. I did a close up of that spot. there is a cap symbol right in the way of the solder track to the cap??? Seems funny to run solder that close, and then stop.
From the + symbol on the board to the - symbol, and to the other leg of the cap is 165vdc. From the - symbol on the board to the other leg of the cap is 8mv, dc.

I test optoisolators by methods from the net. I used my analog meter on both sides, doing a diode type test. Also I did a combination of analog and digital, with the analog triggering the digital side. The opto from the board failed the test, as did a lot of ones from my junk pile. I only found one that marginally passed, it did not make the board work.
Optoisolators are not available here, so while I'm waiting for some to arrive I'm going to build a little tester found on the net.
It's a sad thing that I can't get electronic parts here. Radio Shack is limited in stock, and the only other shop did not have optoisolators with four legs.
I'll try to post some pics, but the schematic I posted should show the connections I have posted here.

[retiredcaps]

Re: Dell monitor

1) On ICE2AS01, pin 6 is your Vcc and pin 7 is GND.

a) What is the DC voltage on pin 6 (using pin 7 for GND)? Is it stable or fluctuating?

2) If C907 is the 47uF cap, what is the DC voltage across (black probe on negative leg and red probe on positive leg) the cap? Is it stable or fluctuating?

3) Schematics definitely help. However, they can't show conductive glue, carbon tracks, burnt components, bloated caps, dodgy soldering, etc. Over the last few weeks, we have had people say "I can't see anything wrong" and we have found a number of obvious problems by looking at photos. I'm not saying you fall into this category, but photos always help.

[momaka]

Re: Dell monitor

13.5V according to (ICE2AS01). "S" not "5".

Thank you

The 47uf cap #c907 is directly connected to the negative (-) leg of the rectifier. The solder track from it goes to the transformer and the (-) symbol on the board. Funny thing, the solder track has a gap right at the cap, but testing shows continuity through the track under it.

I'm not exactly sure what you mean by this. Are you saying cap C907 shows short circuit across its terminals? Also, "shows continuity" doesn't mean much because some multimeters will beep even on a voltage drop as high as 100mV - and that's not really continuity. Measure the *resistance* across the terminals of C907 with the *lowest* scale of your multimeter and post what results you get here.

I did a close up of that spot. there is a cap symbol right in the way of the solder track to the cap??? Seems funny to run solder that close, and then stop.

I think you're getting a little confused here. Look at the monitor schematic again. The transformer has 2 windings on the primary side - a main winding (responsible for producing voltages in all of the other windings in the transformer) and an auxiliary winding (which is used to supply power to the ICE2AS01 controller). The auxiliary winding is connected to hot ground on one side (the "-" of the bridge rectifier and the "-" leg of the big 400V cap). The other side of the auxiliary winding is connected to diode D902. When the PSU is running, current gets rectified through D902, flows through resistor R907, and feeds power to the ICE2AS01 controller on pin 6. C907 is used for smoothing this voltage. That's why its positive leg is connected to pin 6 of the ICE2AS01 chip and its negative leg is connected to hot ground (pin 7, "-" of the bridge rectifier, and "-" of the big 400v cap).

From the + symbol on the board to the - symbol, and to the other leg of the cap is 165vdc.

That's the voltage across the main 400v cap on the primary - that's fine. You are measuring the wrong thing, though. Do as retiredcaps says - measure the voltage between pins 6 and 7 of the ICE2AS01 chip *OR* measure across the terminals of C907.

I test optoisolators by methods from the net.... The opto from the board failed the test, as did a lot of ones from my junk pile. I only found one that marginally passed, it did not make the board work.

Sounds like either your technique or the method you found on the internet is wrong. Like I mentioned, I have my doubts that the optoisolator is bad - they just don't fail that often at all.

[cb92]

Re: Dell monitor

There is 8mv between pin 6&7 on the IC. Same across cap c907.
I try to post the optoisolator test.
I checked e-bay for replacement power supplies, there's plenty from $13 to $25 available. If I can get the monitor to work on a bench power supply, I'll order one. I see why my electronics salesman wondered why I bother to study this thing. I learn by doing and asking questions. Cheap items are not always available, I want to learn how to diagnose power supply problems. I'm concentrating on this one field, 'cause electronics is big-big-big.

[retiredcaps]

Re: Dell monitor

There is 8mv between pin 6&7 on the IC. Same across cap c907.

There is a cap just below c907 that says 25V. What is the DC voltage across it?

I ask because maybe that is the startup cap and not c907?

[cb92]

Re: Dell monitor

I just put everything away, going to move it all to my workshop in town. The bench power supply did run the monitor, so it's only the power supply that is bad. I ordered one from e-bay for about 20 bucks delivered. I'll continue working on the old power supply for my education.
It really gets me that boards can be pristine and not work. I'm used to broken things looking broken. With practice, I'll be able to troubleshoot power supplies. I'm sure the more I work on them, the quicker I'll get to find the problem.

[momaka]

Re: Dell monitor

It really gets me that boards can be pristine and not work.

There is 8mv between pin 6&7 on the IC. Same across cap c907.

Well, that's the problem right there. If you look in the ICE2AS01 data sheet, it tells you that you need to have at least 8.5V on pin 6 (pin 6 is Vcc, the voltage supply pin for the PWM controller).

There's a number of things that can be bad to cause this problem:
1. Diode D902 could be shorted.
2. Either resistor R902 or R903 could be open
3. Resistor R907 could be open (rare, and you would at least see a quick pulse when powering on the PSU)
4. The PWM controller could be bad (rare, but easy to check... more on that in a bit)
5. Capacitor C907 could be shorted (extremely unlikely) or is bad/high ESR (more likely, but again, you will see at least some pulsing on the output of the PSU if this was the case).

So you really have only 6 items to check (item 2 is counted twice since there are 2 resistors). Let's start in order. The list below shows how to troubleshoot each of the problems above.

1. Set your multimeter to diode test. Put the positive probe on the anode of D902 and the negative probe on cathode (cathode is the side marked with a white band on D902). You should get a diode voltage drop on your multimeter (typically 200 mV to 800mV). Now reverse the probes. You should NOT get any reading. If you do, write it down and post what it is here.

2. Desolder either resistor R902 or R903 from the board (doesn't matter which one) - this is done so that you can get an accurate reading since they are high resistance. Measure resistors R902 and R903 with your multimeter. R902 and R903 should both be 39 kOhms +/- 5%. When measuring these resistors, do not touch the metal parts of your multimeter probes as this can impact the readings.
- If resistors R902 and R903 show a resistances higher than 5% of 39 kOhms, replace them.

3. Resistor R907 can be measured in the circuit. Set your multimeter to 200 Ohm scale and measure the resistance. As long as it's not higher than 15 Ohms, it should be fine.

4. One way to test if the PWM controller is bad is to feed it with an external power supply (a 9-12V power supply should be fine). VERY IMPORTANT: the external power supply MUST NOT be grounded! (otherwise you will get a fireworks show). A linear, unregulated power adapter is best suited for this.
How to test the PWM controller with the external power supply...
Wire the "+" of the external power supply to the "+" of capacitor C907 OR to pin 6 of the PWM controller (they are both the same point, so it doesn't matter which one you choose).
Wire the "-" of the external power supply to the "-" of the big 400V capacitor OR to pin 7 of the PWM controller.
Turn the external PSU ON. Then plug in the monitor PSU. The PSU should come on.

5. If you don't have an ESR meter to test capacitor C907, just replace it.

[retiredcaps]

Re: Dell monitor

4. The PWM controller could be bad (rare, but easy to check... more on that in a bit)

You can also see if the two pins are shorted or not as per

https://www.badcaps.net/forum/showth...light=ICE2AS01

[retiredcaps]

Re: Dell monitor

There is a cap just below c907 that says 25V. What is the DC voltage across it?

I ask because maybe that is the startup cap and not c907?

Disregard!!! Major brain fart. Must get some sleep.

[cb92]

Re: Dell monitor

You can also see if the two pins are shorted or not as per

https://www.badcaps.net/forum/showth...light=ICE2AS01

I found that thread, too, makes for good reading. I think I searched the forums first, but did not use the correct term. Lots of good information, I'll do all the tests, sooner or later I will find the culprit.
I would just love it if every time it was the same thing, but probably not to be.

I want to develop a check list for power supplies, so I can do a standard test on each one I encounter.