Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

[PlainBill]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

NP

They are so stupidly simple and yet an amazingly powerful tool.

I've found that some of these trafos have a tickler coil that is AFAIK open ended. It may be capacitively coupled internally, but I've been unable to confirm that. A cap wound into the trafo would be odd. It's used to pass a signal back to the SMPS chip. Ran across it in the Apple PSU's a while back. Confusing because ringing it gave no response and shorting it caused no loss in the other windings.

Yeah, the tertiary winding used to power the SMPS controller. The chances of a capacitor in the transformer is so close to zero as to not be worth mentioning. And that winding open WOULD cause some strange symptoms.

I've got an old Sencore ring tester from the '70's that comes in very handy in cases like that.

PlainBill

[Toasty]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

NP

They are so stupidly simple and yet an amazingly powerful tool.

I've found that some of these trafos have a tickler coil that is AFAIK open ended. It may be capacitively coupled internally, but I've been unable to confirm that. A cap wound into the trafo would be odd. It's used to pass a signal back to the SMPS chip. Ran across it in the Apple PSU's a while back. Confusing because ringing it gave no response and shorting it caused no loss in the other windings.

[PlainBill]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

>>Are we building ourselves a home made ring tester? Haha...I have no idea what one is, but this is cool!<<

https://www.badcaps.net/forum/showth...?t=8231&page=2

Thanks, Toasty. I knew someone would step in with some help.

PlainBill

[Toasty]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

>>Are we building ourselves a home made ring tester? Haha...I have no idea what one is, but this is cool!<<

https://www.badcaps.net/forum/showth...?t=8231&page=2

[PlainBill]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Okay - both of the waveforms appear to be the same. It doesn't look anything like the ring in your image. Is my oscilloscope broken? I don't know why it doesn't display vertical lines.

Also, the square wave generator I speak of is just a basic CMOS oscillator - not an extremely accurate function generator or anything, so the square wave has a very slight corner on one edge of the waveform. Is this going to render the test useless?

That would be a bummer if it was the oscilloscope being broken...it appears to work properly though - a square wave shows horizontal lines only.

So, have any ideas of what to try next?

We are going to have to wait. I've got a similar transformer here; one secondary passes the ring test, the other fails. It might be a day or two before I can hook it up to the scope and square wave generator.

PlainBill

[HexInverter]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Okay - both of the waveforms appear to be the same. It doesn't look anything like the ring in your image. Is my oscilloscope broken? I don't know why it doesn't display vertical lines.

Also, the square wave generator I speak of is just a basic CMOS oscillator - not an extremely accurate function generator or anything, so the square wave has a very slight corner on one edge of the waveform. Is this going to render the test useless?

That would be a bummer if it was the oscilloscope being broken...it appears to work properly though - a square wave shows horizontal lines only.

So, have any ideas of what to try next?

[HexInverter]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Those numbers look very much like the lower side of the transformer has shorted turns in the secondary. At this point I would suggest either replacing it, or using a ring tester to verify shorted turns. No ring tester? Keep reading.

You had mentioned earlier that you had used a square wave to check the scope. Unsolder the transformer and hook one secondary across the output of the square wave generator. Hook the scope probe to the output of the square wave generator. You should see ringing like in the attached picture. Now try the other secondary. If they both show the same number of rings, the transformer is good. If only one secondary shows ringing, the transformer is bad. If neither shows ringing, I may be giving you bad advice.

PlainBill

Are we building ourselves a home made ring tester? Haha...I have no idea what one is, but this is cool!

Off to try that, I'll report back in a bit!

[PlainBill]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Those numbers look very much like the lower side of the transformer has shorted turns in the secondary. At this point I would suggest either replacing it, or using a ring tester to verify shorted turns. No ring tester? Keep reading.

You had mentioned earlier that you had used a square wave to check the scope. Unsolder the transformer and hook one secondary across the output of the square wave generator. Hook the scope probe to the output of the square wave generator. You should see ringing like in the attached picture. Now try the other secondary. If they both show the same number of rings, the transformer is good. If only one secondary shows ringing, the transformer is bad. If neither shows ringing, I may be giving you bad advice.

PlainBill

[HexInverter]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

The buzzing is significant; that may have to be investigated.

Here is a quick summary of what happens when the monitor is powered up.
The power supply comes up. The processor(s) on the logic card initialize, and determine the last status. In this case, the status was 'On', so the inverter controller is switched on, and the processors look for a video signal.

The inverter controller drives the transformers (you actually have two transformers in one package) at full power while monitoring the voltage across and current through the CCFLs. If the voltage goes too high it will reduce the drive. As the CCFLs ignite the current rises and the controller reduces the drive. If the voltage across any CCFL is too high or the current through any CCFL is too low or too high the controller shuts down. This whole sequence takes a couple of seconds.

In the meantime the processor is displaying the video signal, if present. After 5-10 seconds without video signal the processor will switch the power LED to orange and turn the inverter off.

Now, back to troubleshooting. The waveform you should be seeing on V1 - V4 should be under 3 volts at about 100 Khz. The waveform at I1 - I4 should be over 3 volts and at the same frequency.

The fact that the 'non-contact' voltage is different at the two ends and the buzzing sound indicates a possible short. I'd suggest seeing if you can measure a voltage at V3 and V4, and I3 and I4.

PlainBill

Okay! Hopefully this means something I can only assume that this many zero voltages readings is a bad thing

I took my DMM and measured all of the points. Just like the oscilloscope, there's only ever a reading when the transformers buzz. I was pretty sure they are AC voltages, as someone mentioned near the beginning of the thread that everything's AC after the SMT FET, but figured I'd measure both AC and DC in case I was wrong.

Here are the results (I have put a "/" between results. The first result is the first time the transformers buzz, and the second is the second buzz of the transformer.)

AC Voltage Tests

V1: 14.7v / 12.6v
V2: 17.3v / 16.5v
V3: 8.6v / 8.5v
V4: 8.1v / 8.0v

I1: Zero / Zero
I2: Zero / Zero
I3: Very small number (.1v I think it was) / Zero!
I4: Zero / Zero


DC Voltage Tests

V1: 6.89v / 6.54v
V2: 8.22v / 7.84v
V3: 4.16v / 4.16v
V4: 3.4v / 3.4v

I1: Zero / Zero
I2: Zero / Zero
I3: .01v / Zero
I4: .05v / Zero

As for probing with the scope, I was having an impossible time trying to get a waveform on anything but the non contact transformer test. I think it would help if I had some way of securing the probe lead to the pad while playing with the scope settings. As it stands, I only have those IC leg clip on probes, so they're not very good for solder pads I did switch it on and off a bunch trying to get a reading as the transformers are powered on for those few seconds, but couldn't manage to get anything.

[PlainBill]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Okay, well I just got back from trying these tests out...

I tested the scope just to make sure I can get a waveform on it with a simple square wave oscillator. No problemo, so I think it works. Onto the tests...

When testing over the transformer, I can't get a stable waveform - though there is one when the buzzing I described earlier happens.

This is what happens:

- I turn the monitor/power bar on, the blue power LED comes on
- A moment later, there is a buzzing sound coming from the board. At this point, the oscilloscope displays a waveform that is either noise, or I just can't get focused on it for the second that the transformer is on
- The buzzing stops a second later, and the oscilloscope displays nothing.
- The board waits another second, then buzzes again, then stops - same thing.
- The power LED turns orange.

After that, there is nothing displayed on the oscilloscope, and no buzzing. I assumed this is what you meant by not getting a waveform and went onto the next test, but I went to point V1, and tried numerous settings with the probe clipped on there. I cannot get a waveform to display for V1! Weird.

Out of curiosity, I went back and forth between the top and bottom transformer points. The top one displays a higher amplitude waveform than the bottom. Does that matter, or is the amplitude relative to how close I am placing the probe on the board? Whether the waves are the same or not in frequency or shape, I can't tell because it's just a blur of lines for the second it's on.

Does this mean the whole board is losing power (is that possible?) or am I just not using the scope right somehow?

The buzzing is significant; that may have to be investigated.

Here is a quick summary of what happens when the monitor is powered up.
The power supply comes up. The processor(s) on the logic card initialize, and determine the last status. In this case, the status was 'On', so the inverter controller is switched on, and the processors look for a video signal.

The inverter controller drives the transformers (you actually have two transformers in one package) at full power while monitoring the voltage across and current through the CCFLs. If the voltage goes too high it will reduce the drive. As the CCFLs ignite the current rises and the controller reduces the drive. If the voltage across any CCFL is too high or the current through any CCFL is too low or too high the controller shuts down. This whole sequence takes a couple of seconds.

In the meantime the processor is displaying the video signal, if present. After 5-10 seconds without video signal the processor will switch the power LED to orange and turn the inverter off.

Now, back to troubleshooting. The waveform you should be seeing on V1 - V4 should be under 3 volts at about 100 Khz. The waveform at I1 - I4 should be over 3 volts and at the same frequency.

The fact that the 'non-contact' voltage is different at the two ends and the buzzing sound indicates a possible short. I'd suggest seeing if you can measure a voltage at V3 and V4, and I3 and I4.

PlainBill

[HexInverter]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Okay, well I just got back from trying these tests out...

I tested the scope just to make sure I can get a waveform on it with a simple square wave oscillator. No problemo, so I think it works. Onto the tests...

When testing over the transformer, I can't get a stable waveform - though there is one when the buzzing I described earlier happens.

This is what happens:

- I turn the monitor/power bar on, the blue power LED comes on
- A moment later, there is a buzzing sound coming from the board. At this point, the oscilloscope displays a waveform that is either noise, or I just can't get focused on it for the second that the transformer is on
- The buzzing stops a second later, and the oscilloscope displays nothing.
- The board waits another second, then buzzes again, then stops - same thing.
- The power LED turns orange.

After that, there is nothing displayed on the oscilloscope, and no buzzing. I assumed this is what you meant by not getting a waveform and went onto the next test, but I went to point V1, and tried numerous settings with the probe clipped on there. I cannot get a waveform to display for V1! Weird.

Out of curiosity, I went back and forth between the top and bottom transformer points. The top one displays a higher amplitude waveform than the bottom. Does that matter, or is the amplitude relative to how close I am placing the probe on the board? Whether the waves are the same or not in frequency or shape, I can't tell because it's just a blur of lines for the second it's on.

Does this mean the whole board is losing power (is that possible?) or am I just not using the scope right somehow?

[PlainBill]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Okay, I've got the whole thing rigged up and ready to go - just one more thing before I proceed with the tests, if you don't mind.

When you say the oscilloscope ground goes to the inverters corner ground plane, do you mean the ground clip on the probe, or the oscilloscope's ground connector on the bottom right in the picture I attached? I've always used the probe's ground for low current/voltage circuits, without hooking up the ground on the oscilloscope, but I have no idea which one to use for a line powered device like this. If I had to guess, I'd think the oscilloscope's ground is there for when running on battery mode (and not properly earth grounded)?

It's a battery powered oscilloscope running off of the wall plug - it's connected to a properly earthed circuit with a 3 prong plug right now - I read somewhere you could create a ground loop, and that would be bad if you do it wrong, so figured I'd check before doing something potentially stupid

Caution is good. The probe's ground would go to the ground for the power supply / inverter. If you visualize the monitor assembled the ground pin on the power cord, the DC ground on the power supply, and the metal shell on the VGA connector are all connected to the metal cover over the logic card and power supply.

PlainBill

[HexInverter]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Okay, I've got the whole thing rigged up and ready to go - just one more thing before I proceed with the tests, if you don't mind.

When you say the oscilloscope ground goes to the inverters corner ground plane, do you mean the ground clip on the probe, or the oscilloscope's ground connector on the bottom right in the picture I attached? I've always used the probe's ground for low current/voltage circuits, without hooking up the ground on the oscilloscope, but I have no idea which one to use for a line powered device like this. If I had to guess, I'd think the oscilloscope's ground is there for when running on battery mode (and not properly earth grounded)?

It's a battery powered oscilloscope running off of the wall plug - it's connected to a properly earthed circuit with a 3 prong plug right now - I read somewhere you could create a ground loop, and that would be bad if you do it wrong, so figured I'd check before doing something potentially stupid

[HexInverter]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

You've got a bad habit of taking close up shots rather than a single all - over shot. I've got a problem linking the various pictures to together. But the first picture on this page gives me all the information I need.

This is pretty simple. You MUST have the power supply / inverter hooked to both the CCFLs and the logic card. You also must have access to the back side of the power supply / inverter. You should have the front panel hooked to the logic card. It is desirable, but not absolutely necessary to have the LCD panel hooked to the logic card.

In situations like this I like to take a piece of the pink foam that usually comes with motherboards and use that as an insulator between the cards and the back of the LCD panel. I'll then hook the ground traces of the power supply to the back shell of the LCD panel. A primary consideration of this arrangement is you must avoid contacting the area of the power supply that is at 165 (or higher) volts. That would be uncomfortable.

PlainBill

Great, makes sense now - thanks! Sorry for all my silly questions by the way...I'm one of those people that can't stand being unsure about something...especially when it's line voltage I'm dealin' with!

Yeah...I'm real bad with those close ups. I don't have a tripod for my camera, and the image stabilization on it is AWFUL you can't take a clear shot unless it's on a tripod or your arms are rested up against something - hence why my shots are always up close (resting my forearms/wrists or elbows on the table).

Off to scope-n'!

[PlainBill]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Okay Bill, so while getting all set up for this, I've run across an issue (maybe?) and just wanted to get some clarification before I plug anything into line voltage - As you can see form these shots, the inverter backplate design isn't going to let me test it in its chassis with everything hooked up the way it's supposed to be. The limiting factor appears to be the short, wider ribbon cable that goes from the logic board to the LCD.

So, for these tests - I think I either need to not have the LCD plugged into the logic board, or I need to unscrew the inverter/logic board from the chassis and put it on some insulating material for the test.

Which is preferred, or do you have some other idea judging by the pictures?

Thanks kindly

You've got a bad habit of taking close up shots rather than a single all - over shot. I've got a problem linking the various pictures to together. But the first picture on this page gives me all the information I need.

This is pretty simple. You MUST have the power supply / inverter hooked to both the CCFLs and the logic card. You also must have access to the back side of the power supply / inverter. You should have the front panel hooked to the logic card. It is desirable, but not absolutely necessary to have the LCD panel hooked to the logic card.

In situations like this I like to take a piece of the pink foam that usually comes with motherboards and use that as an insulator between the cards and the back of the LCD panel. I'll then hook the ground traces of the power supply to the back shell of the LCD panel. A primary consideration of this arrangement is you must avoid contacting the area of the power supply that is at 165 (or higher) volts. That would be uncomfortable.

PlainBill

[HexInverter]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

I should say, I am unsure of the safety of removing the PCB's from what I assume is the earth grounded chassis holding them there - is this safe? Do I even need the logic board plugged in to run these tests?

I can't see any way of manipulating that super short cable without losing something (LCD connectivity or the metal casing the boards are screwed into)

[jetadm123]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Nice to have the boards facing you foil side up. Makes it way easier to take voltage and scope readings.

[HexInverter]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Did you mean to attach some pictures with this post? If yes, they didn't show up. This site has a 2000x2000 and I believe 1.7MB limit per picture.

Lol! Oops Forgot to attach 'em!

Here goes:

[retiredcaps]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Which is preferred, or do you have some other idea judging by the pictures?

Did you mean to attach some pictures with this post? If yes, they didn't show up. This site has a 2000x2000 and I believe 1.7MB limit per picture.

[HexInverter]

Re: Acer x193w with Darfon B092-XXX inverter - assistance needed! [lotsa pics!]

Okay Bill, so while getting all set up for this, I've run across an issue (maybe?) and just wanted to get some clarification before I plug anything into line voltage - As you can see form these shots, the inverter backplate design isn't going to let me test it in its chassis with everything hooked up the way it's supposed to be. The limiting factor appears to be the short, wider ribbon cable that goes from the logic board to the LCD.

So, for these tests - I think I either need to not have the LCD plugged into the logic board, or I need to unscrew the inverter/logic board from the chassis and put it on some insulating material for the test.

Which is preferred, or do you have some other idea judging by the pictures?

Thanks kindly