HP w20 LCD Display Inverter, running out of options.

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

Both jumpers on, diplay don't turn off.
- tested 4 hours

One jumper on, one off, display don't turn off.
- tested with either for 4 hours.

After soldering last jumper off (display still hot) and
turning it back on after this, 2 secs to black.

So both sides are required without jumpers for failure

[PlainBill]

Re: HP w20 LCD Display Inverter, running out of options.

Thanks PlainBill.

Points are now grounded. I had it on 3,5 hours without any problems, finally I set brightness to 0 and back to 95 several times. No problems whatsoever. I had to quit testing for a while, but I'm running it again now to make sure.
What if it does not shut down? Should I remove one wire at a time to see which side is failing?

P.S. I got brief access to that REV 3 monitor again. Measured about half resistances for R1 & R5 compared to this REV 2 board.

R1 0.68 M ohms to GND
R2 98 ohms
R3 98 ohms
V1 98 ohms
----------

V2 98 ohms
R4 98 ohms
R5 0.68 M ohms
R6 98 ohms

Exactly, remove one jumper at a time. Then we start identifying what is causing the failure.

PlainBill

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

The fog has just lifted from my brain. We don't have to know HOW those transformers work, they probably aren't in the fault detection circuit anyway. We just have to figure out where the voltage spike is coming from.

To that end, here are a couple of things to try. I've circled the low voltage end of the two high voltage caps used in the sense circuitry. As a first step, I suggest grounding both those points. The easiest way might be to solder a short piece of wire across the locations for C19 and C25 (verify those actually short it to ground). Then test the monitor for a minimum of several hours - longer is better. If it doesn't shut down, we can be sure the problem is coming from one of those two points.

If it does shut down, we know something else is feeding in a fault signal.

PlainBill

Thanks PlainBill.

Points are now grounded. I had it on 3,5 hours without any problems, finally I set brightness to 0 and back to 95 several times. No problems whatsoever. I had to quit testing for a while, but I'm running it again now to make sure.
What if it does not shut down? Should I remove one wire at a time to see which side is failing?

P.S. I got brief access to that REV 3 monitor again. Measured about half resistances for R1 & R5 compared to this REV 2 board.

R1 0.68 M ohms to GND
R2 98 ohms
R3 98 ohms
V1 98 ohms
----------

V2 98 ohms
R4 98 ohms
R5 0.68 M ohms
R6 98 ohms

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

Seems to me that CP7 would connect C36 parallel with C12 and CP8 would add a cap C35 parallel with C10 adding some capacitance.

[PlainBill]

Re: HP w20 LCD Display Inverter, running out of options.

Thanks PlainBill. Before I try that shorting to ground, what do you think about these disconnected spots?

I really can't figure out why they would build circuitry with several resistors and capacitors not connected from another side. Could this be on purpose or might it be a manufacturing defect?

At least R45 might be involved with current sense feedback (PIN 5 in IC) if CP1 would be connected. And on the other side PIN 13 (timing capasitor) might be missing two caps because CP7 and CP8 are not connected.

I did not notice these before I had this better image and started measuring different points here.

This is quite common. In many cases one board will be designed for several different applications, and depending on the needs only certain parts will be loaded.

At one point in my checkered career my employer used the same board for about 20 different products. Depending on the configuration the board could be fully loaded, or each input channel could feature a single jumper from input connector to the multiplexer, with 75% of the board unused.

PlainBill

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

Thanks PlainBill. Before I try that shorting to ground, what do you think about these disconnected spots?

I really can't figure out why they would build circuitry with several resistors and capacitors not connected from another side. Could this be on purpose or might it be a manufacturing defect?

At least R45 might be involved with current sense feedback (PIN 5 in IC) if CP1 would be connected. And on the other side PIN 13 (timing capasitor) might be missing two caps because CP7 and CP8 are not connected.

I did not notice these before I had this better image and started measuring different points here.

[PlainBill]

Re: HP w20 LCD Display Inverter, running out of options.

The fog has just lifted from my brain. We don't have to know HOW those transformers work, they probably aren't in the fault detection circuit anyway. We just have to figure out where the voltage spike is coming from.

To that end, here are a couple of things to try. I've circled the low voltage end of the two high voltage caps used in the sense circuitry. As a first step, I suggest grounding both those points. The easiest way might be to solder a short piece of wire across the locations for C19 and C25 (verify those actually short it to ground). Then test the monitor for a minimum of several hours - longer is better. If it doesn't shut down, we can be sure the problem is coming from one of those two points.

If it does shut down, we know something else is feeding in a fault signal.

PlainBill

[PlainBill]

Re: HP w20 LCD Display Inverter, running out of options.

Maybe this explains voltage differences?

R1 1.22 M ohms to GND
R2 92.2 ohms
R3 92.2 ohms
V1 92.2 ohms
----------

V2 92.2 ohms
R4 92.2 ohms
R5 1.12 M ohms
R6 92.2 ohms

That would do it. Now why the different resistors?

PlainBill

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

You've given me some excellent numbers, I'm going to have to think about them. One thing is obvious - the over voltage sensing circuit is not close to the point where it should trigger. Another point is that two of the return lines have a higher voltage than the others. I'm going to have to think about this for a while. It appears some serious effort to find a schematic for a monitor using the small transformers is in order.

PlainBill

Maybe this explains voltage differences?

R1 1.22 M ohms to GND
R2 92.2 ohms
R3 92.2 ohms
V1 92.2 ohms
----------

V2 92.2 ohms
R4 92.2 ohms
R5 1.12 M ohms
R6 92.2 ohms

[PlainBill]

Re: HP w20 LCD Display Inverter, running out of options.

You've given me some excellent numbers, I'm going to have to think about them. One thing is obvious - the over voltage sensing circuit is not close to the point where it should trigger. Another point is that two of the return lines have a higher voltage than the others. I'm going to have to think about this for a while. It appears some serious effort to find a schematic for a monitor using the small transformers is in order.

PlainBill

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

While waiting for lights to go off I started adjusting brightness to lower
level (from 95%) and suddenly lights wen't off when I reached 55%.

So I started testing off/on procedure on DC voltages.
No peaks seem to occur on R1-R6, voltages just disappear.

Suddenly monitor started again and seems to go back to normal operation.

So I decided to try adjusting brightness again. It was at 95% as I was unable
to save settings last time. Again, when it reaches 52%, lights go off.

Have I found a pattern? Let's try third time in a row. With brighness
set to 95% monitor stays on. Reducing brightness again and this time at 57% lights go off.

This eguipment has been playing me so long. I have to try 4th time, and again, now at 45% lights go off. When I turn it on it stays on (brightness is set to 95% from memory).

I think I've found a pattern. Fifth time in a row, now I had to go
down to 30% before lights go off. Big changes in brightness seem to cause ligths to shutdown.

Restarting but now it won't start. Hmm. put diode in place (took like 5 secs)
as I have it in external connector. Menu shows brightness of 30%? What? I did not save it, why it's kept? Now I set brightness back up to 95%, take diode hack off and It stays on again.

After few minutes I set brightness to 75%. Within 2 minutes backlights go off.

Diode back in. Brightness up to 95%.

Turn on.
Measure:
Point DC AC
R1 0.78 72
R2 0 44
R3 0 40
V1 0.20 0.4

V2 0.19 0.4
R4 0 48
R5 0.82 69
R6 0 37

Now it stayed on about 2 minutes. Then it shuts down, even at 95% brightness.

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

Darn thing just won't die anymore. It's like it knows I'm waiting. Stubborn display! Still on and showing:


R1
V 0.84
V~ 60

R2
V 0
V~ 43

R3
V 0
V~ 30

V1
V 0.19
V~ 0.4

-----------

V2
V 0.18
V~ 0.4

R4
V 0
V~ 37

R5
V 0.85
V~ 63

R6
V 0
V~ 39

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

Thanks PlainBill.

Started with 50% brightness

V V~
Orange R1 0.51 51.6
Ora/wihte R2 0 31.4
blue R3 0 33.7
blue/whi V1 0.146 0.3

gre/whi V2 0.128 0.3
green R4 0 29.7
brown R5 0.56 44.5
brown/whi R6 0 26.4

Turned brightness to 95% (V~ increases while metering, starts from about 5-10 volts lower each time, probably multimeter problem. I took value after measuring point about 5 secs when rising slows)
V V~
Orange R1 0.79 80.0
Ora/whi R2 0 61
blue R3 0 44
blue/whi V1 0.20 0.4

gre/whi V2 0.18 0.4
green R4 0 55
brown R5 0.82 71
brown/whi R6 0 44


95% brightness after 25 minutes just before lights wen't off.

V V~
Orange R1 0.79 71.0
Ora/whi R2 0 50
blue R3 0 40
blue/whi V1 0.20 0.4

gre/whi V2 0.18 0.4
green R4 0 54
brown R5 0.84 67
brown/whi R6 0 35


on, off.. it started and stays on....

V V~
Orange R1 0.81 70
Ora/whi R2 0 50
blue R3 0 40
blue/whi V1 0.20 0.4

gre/whi V2 0.19 0.4
green R4 0 48
brown R5 0.84 60
brown/whi R6 0 37

lights off... ok now I can get peak values

blue/whi V1 0.23 0.4
gre/whi V2 0.26 0.4

Pushed off/on button and got these peaks before lights went't off,
but then it started "normally" again and I could not measure
possible peaks on R -spots. Values after restarting.

V V~
Orange R1 0.81 69
Ora/whi R2 0 49
blue R3 0 40
blue/whi V1 0.20 0.4

gre/whi V2 0.19 0.4
green R4 0 44
brown R5 0.84 66
brown/whi R6 0 42


10 minutes after restart

V V~
Orange R1 0.83 66
Ora/whi R2 0 46
blue R3 0 35
blue/whi V1 0.20 0.4

gre/whi V2 0.19 0.4
green R4 0 46
brown R5 0.84 65
brown/whi R6 0 35

Now it's been working half an hour without
diode hack.

Seems I can't format this page properly. In each line there are both voltages. First one is DC and secon AC value.

[PlainBill]

Re: HP w20 LCD Display Inverter, running out of options.

Thanks again PlainBill I really appreciate your advices. I don't understand this neither. I did factory reset for this monitor when I started with it and I keep wondering why on earth I've spent 120 hours and 113 backlight hours with it already. I must be insane. Luckily enough others are involved too so I'm not the only crazy one here.

I've been using this diode "hack" of yours and monitor stays on forever (allready 6 hours now) without any problems. I may not have knowledge or experience required to make any good guesses but I'm starting to believe that there is indeed a problem in OVP circuitry as you mentioned. (shame on me, I have no idea where it it or how it works).

- Monitor stays on with perfect picture and stable brightness god nows how long when diodes are in place.
- There is nothing wrong in CCFL's as another board works fine with them.
- There is no overheating problem. REV 3 monitors temperature is 51.1 centigrades and my failing REV 2 monitor is only 47.1 centigrades measured at exactly same spot above circuitry with same 50% brightness.

I will measure R1-R6 and V1 - V2 next but I suspect that OVP circuitry is bad and does something it should not do...

That is very likely.

I've attached a schematic of a typical inverter, which will give you an idea of what we are dealing with. C8 and C13 they form a voltage divider. The significant point is that the voltage at the junction is a very small fraction of the output voltage of the transformer. Something like 22/33022 to be exact. CR2 shunts the negative spikes to ground while passing the positive spikes to C16 and R14. C14 charges to the peak value (less 0.7 volts) of the positive spikes.

Yours has some differences. The first is that on yours C13 has been replaced with a resistor. The second is there are two such networks.

Back to the schematic, CR1, R16 and R15 for a network to feed a voltage representing the current through the CCFLs back to the inverter. Yours is much more complicated. I don't really understand how yours works, hopefully I will find a schematic of a similar inverter.

Clearly, yours has an intermittent problem. The diodes I had you add should not stop the intermittent, they only prevent it causing a shut down. I am hoping that by measuring the return currents and the output voltages when the monitor is first turned on, and again after it would normally fail we will be able to identify a particular path that causes the problem.

PlainBill

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

First, I must be honest. I don't full understand what was causing the failure. The inverter is designed to produce a constant current through the CCFLs. One possibility was one of the transformers on the return lines was intermittent. When it failed to sense the current from one or more CCFLS the controller would increase the output, thus tripping the over voltage protect. You have indicated the brightness no longer increases, which shoots down that theory. The other possibility is that there is a problem with the OVP circuitry.

Points R1-R6 are the return lines, and should have voltages of less than 2 volts; well within the range of your meter. Likewise, V1 and V2 are after a voltage divider capacitor. The voltages at those point should also be quite low.

However, I have had several meters die an untimely death because of inadvertent application of high voltage and would prefer not to be responsible for it happening to others. I've marked up the areas to avoid.

PlainBill

Thanks again PlainBill I really appreciate your advices. I don't understand this neither. I did factory reset for this monitor when I started with it and I keep wondering why on earth I've spent 120 hours and 113 backlight hours with it already. I must be insane. Luckily enough others are involved too so I'm not the only crazy one here.

I've been using this diode "hack" of yours and monitor stays on forever (allready 6 hours now) without any problems. I may not have knowledge or experience required to make any good guesses but I'm starting to believe that there is indeed a problem in OVP circuitry as you mentioned. (shame on me, I have no idea where it it or how it works).

- Monitor stays on with perfect picture and stable brightness god nows how long when diodes are in place.
- There is nothing wrong in CCFL's as another board works fine with them.
- There is no overheating problem. REV 3 monitors temperature is 51.1 centigrades and my failing REV 2 monitor is only 47.1 centigrades measured at exactly same spot above circuitry with same 50% brightness.

I will measure R1-R6 and V1 - V2 next but I suspect that OVP circuitry is bad and does something it should not do...

[PlainBill]

Re: HP w20 LCD Display Inverter, running out of options.

Somehow I expected this



No, backlights don't shutdown now with diodes is place and brightness seems to stay normal. Brightness increase used to happen just split second before shutdown.



Yes, it's grounded with pins 14 and 16. It's marked as "91R0". Multimeter says it's 91.5 ohms. R52 on "mirror" side is alike and also grounded.



Should I remove diodes and use monitor untill backlights go off. Then I might get some readings by turning it on and off like when measuring IC. I need to get measure points out of the monitor again. Just to be on safe side, are we talking about huge voltages on points R1-R6? My multimeters max is 600V and these spots are so connected to CCFL's...

First, I must be honest. I don't full understand what was causing the failure. The inverter is designed to produce a constant current through the CCFLs. One possibility was one of the transformers on the return lines was intermittent. When it failed to sense the current from one or more CCFLS the controller would increase the output, thus tripping the over voltage protect. You have indicated the brightness no longer increases, which shoots down that theory. The other possibility is that there is a problem with the OVP circuitry.

Points R1-R6 are the return lines, and should have voltages of less than 2 volts; well within the range of your meter. Likewise, V1 and V2 are after a voltage divider capacitor. The voltages at those point should also be quite low.

However, I have had several meters die an untimely death because of inadvertent application of high voltage and would prefer not to be responsible for it happening to others. I've marked up the areas to avoid.

PlainBill

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

With great difficulty.

Somehow I expected this

There is a LOT of circuitry involved and I've never figured out how this particular design works. Let's give it the old college try.

Early in this thread you indicated the brightness would increase, followed by shutdown. Is the brightness still increasing with the diode blocking the shutdown?

No, backlights don't shutdown now with diodes is place and brightness seems to stay normal. Brightness increase used to happen just split second before shutdown.

I've marked up the picture of the bottom of the board. First of all, I've dotted one end of R53. Is that point connected to ground (pin 14 or 16 of IC1)?

What are the numbers on R53?

Yes, it's grounded with pins 14 and 16. It's marked as "91R0". Multimeter says it's 91.5 ohms. R52 on "mirror" side is alike and also grounded.

I've marked 6 points R1 - R6. These are the six return lines from the CCFLs. Measure the voltage on them first at turn-on, then after the brightness (would have) increased.

I have also marked two points V1 and V2. These are the voltage sense lines from the inverter outputs. Again, measure the voltage at turn-on and after the brightness (would have) increased.

PlainBill

Should I remove diodes and use monitor untill backlights go off. Then I might get some readings by turning it on and off like when measuring IC. I need to get measure points out of the monitor again. Just to be on safe side, are we talking about huge voltages on points R1-R6? My multimeters max is 600V and these spots are so connected to CCFL's...

[PlainBill]

Re: HP w20 LCD Display Inverter, running out of options.

Thank you PlainBill. I finally managed to get two 1N4148's today and soldered them to IC as you suggested.

I'm not sure should I say Oh joy . I've been burning it now for 4 hours and it does not shut down anymore. So the controller is good? How can I troubleshoot inputs?

With great difficulty. There is a LOT of circuitry involved and I've never figured out how this particular design works. Let's give it the old college try.

Early in this thread you indicated the brightness would increase, followed by shutdown. Is the brightness still increasing with the diode blocking the shutdown?

I've marked up the picture of the bottom of the board. First of all, I've dotted one end of R53. Is that point connected to ground (pin 14 or 16 of IC1)?

What are the numbers on R53?

I've marked 6 points R1 - R6. These are the six return lines from the CCFLs. Measure the voltage on them first at turn-on, then after the brightness (would have) increased.

I have also marked two points V1 and V2. These are the voltage sense lines from the inverter outputs. Again, measure the voltage at turn-on and after the brightness (would have) increased.

PlainBill

[CapBlown]

Re: HP w20 LCD Display Inverter, running out of options.

Again, good work. The reading at pin 10 proves the inverter is shutting off due to a fault condition, not a command from the logic card. There is no point in monitoring pin 5, we know that won't cause the controller to shut down. Either the voltage on pin 6 is triggering it, or the controller itself is bad.

Try this. Place a pair of switching diodes (1N4148 or equivalent) in series from pin 6 (anode) to pin 14 (cathode). This will clamp the voltage at pin 6 to no more than 1.7 volts. If the inverter still shuts down, the controller is bad. If it doesn't shut down, we will have to troubleshoot the individual inputs (Oh, joy!!).

PlainBill

Thank you PlainBill. I finally managed to get two 1N4148's today and soldered them to IC as you suggested.

I'm not sure should I say Oh joy . I've been burning it now for 4 hours and it does not shut down anymore. So the controller is good? How can I troubleshoot inputs?

[PlainBill]

Re: HP w20 LCD Display Inverter, running out of options.

Again, good work. The reading at pin 10 proves the inverter is shutting off due to a fault condition, not a command from the logic card. There is no point in monitoring pin 5, we know that won't cause the controller to shut down. Either the voltage on pin 6 is triggering it, or the controller itself is bad.

Try this. Place a pair of switching diodes (1N4148 or equivalent) in series from pin 6 (anode) to pin 14 (cathode). This will clamp the voltage at pin 6 to no more than 1.7 volts. If the inverter still shuts down, the controller is bad. If it doesn't shut down, we will have to troubleshoot the individual inputs (Oh, joy!!).

PlainBill