HP 1825 Display Black Power Light Green

[printone2]

Re: HP 1825 Display Black Power Light Green

I figured out what was wrong. I was having trouble cleaning the holes out on the image card since they appear to be so small. The holes on the power supply are much larger and easy to work with. I decided not to clean the small holes on the image card and just heat them up and push the new caps in while the solder is molten.

I replaced the 470uf 25v caps on the image card and the image card works now. It does look like one of the inverter cards is bad on one of the panels, but that is going to have to wait until I can see if the 3rd panel's inverter is working.

Thanks.

[printone2]

Re: HP 1825 Display Black Power Light Green

I am in the process of replacing the image card caps, but having some trouble getting my Hakko 907 pencil set to the right temp. At 750f it seems to not melt and release the old caps very well. I am using 60/40 solder, but I just noticed that the solder joints look a bit dull on some of the larger lead joints. Do I need to switch to a higher temp if this is no lead solder? Should I also change to no lead solder? The leads of the old caps are sometimes coming out of the can before they are coming off the board.

I figured out what was wrong. I was having trouble cleaning the holes out on the image card since they appear to be so small. The holes on the power supply are much larger and easy to work with. I decided not to clean the small holes on the image card and just heat them up and push the new caps in while the solder is molten.

[printone2]

Re: HP 1825 Display Black Power Light Green

I worked on a Gateway monitor that had a nice image, but on occasion, wavy lines would appear in the background. The logic board also had 470 caps crammed into 8mm cans. Replacing them solved the problem. I suspect that it wasn't stress that killed them, but the heat from the tight enclosure dried them out.

I am in the process of replacing the image card caps, but having some trouble getting my Hakko 907 pencil set to the right temp. At 750f it seems to not melt and release the old caps very well. I am using 60/40 solder, but I just noticed that the solder joints look a bit dull on some of the larger lead joints. Do I need to switch to a higher temp if this is no lead solder? Should I also change to no lead solder? The leads of the old caps are sometimes coming out of the can before they are coming off the board.

[jetadm123]

Re: HP 1825 Display Black Power Light Green

Does it make sense that the caps on the image card were stressed more than the caps on the power supply. My thoughts are that the caps are both 470uf 25v, but the caps on the image card are in a smaller case. Both caps are 10mm in diameter, but the image caps are only 8mm high while the power supply caps are 10mm high. Therefore I expect that the smaller size cased caps would wear out faster, which would explain that the power supply card are working and 2 of 3 image cards failed. I cannot verify that the image card caps are the root problem yet. Is my reasoning very likely?

I worked on a Gateway monitor that had a nice image, but on occasion, wavy lines would appear in the background. The logic board also had 470 caps crammed into 8mm cans. Replacing them solved the problem. I suspect that it wasn't stress that killed them, but the heat from the tight enclosure dried them out.

[printone2]

Re: HP 1825 Display Black Power Light Green

Not really. A common design for the logic board takes the 5V output of the power supply and uses it to feed two LDO regulators and the LCD panel. LDO regulators are linear devices, so there is not the high surge current found in the SMPS. The two LDO regulators supply 3.3V and 1.8V for the processor on the logic card.

PlainBill

Thanks Bill.

[PlainBill]

Re: HP 1825 Display Black Power Light Green

Does it make sense that the caps on the image card were stressed more than the caps on the power supply. My thoughts are that the caps are both 470uf 25v, but the caps on the image card are in a smaller case. Both caps are 10mm in diameter, but the image caps are only 8mm high while the power supply caps are 10mm high. Therefore I expect that the smaller size cased caps would wear out faster, which would explain that the power supply card are working and 2 of 3 image cards failed. I cannot verify that the image card caps are the root problem yet. Is my reasoning very likely?

Not really. A common design for the logic board takes the 5V output of the power supply and uses it to feed two LDO regulators and the LCD panel. LDO regulators are linear devices, so there is not the high surge current found in the SMPS. The two LDO regulators supply 3.3V and 1.8V for the processor on the logic card.

PlainBill

[printone2]

Re: HP 1825 Display Black Power Light Green

Since I pointed out earlier that the original "bad" video card had good input voltage, but yet you still had no image (even with the backlights off, but power led on) leads me to believe that the scaler (video) chip could be fried. I still would check the basics: check for fuses, bad solder joints, caps could also be bad. Really difficult/time consuming to check that board.

What I do recommend is replacing the Capxon caps (with the exception of the large main cap) on the power board with Panasonic FM/FC series caps. The fact that the original caps lasted this long falls under the category of "miracle".

Does it make sense that the caps on the image card were stressed more than the caps on the power supply. My thoughts are that the caps are both 470uf 25v, but the caps on the image card are in a smaller case. Both caps are 10mm in diameter, but the image caps are only 8mm high while the power supply caps are 10mm high. Therefore I expect that the smaller size cased caps would wear out faster, which would explain that the power supply card are working and 2 of 3 image cards failed. I cannot verify that the image card caps are the root problem yet. Is my reasoning very likely?

[jetadm123]

Re: HP 1825 Display Black Power Light Green

I have swapped the logic card and now I have a panel that lights up. Thanks everyone.

My next question is how can I test out the problem with the logic card? I have one other lcd with this same problem, so if I could fix the logic card, I might would have two good panels and one cracked panel.

I do not see any solder joints that look like they need reflowed, but mine is not a trained eye.

Since I pointed out earlier that the original "bad" video card had good input voltage, but yet you still had no image (even with the backlights off, but power led on) leads me to believe that the scaler (video) chip could be fried. I still would check the basics: check for fuses, bad solder joints, caps could also be bad. Really difficult/time consuming to check that board.

What I do recommend is replacing the Capxon caps (with the exception of the large main cap) on the power board with Panasonic FM/FC series caps. The fact that the original caps lasted this long falls under the category of "miracle".

[printone2]

Re: HP 1825 Display Black Power Light Green

Go ahead and swap in the logic/video card

I have swapped the logic card and now I have a panel that lights up. Thanks everyone.

My next question is how can I test out the problem with the logic card? I have one other lcd with this same problem, so if I could fix the logic card, I might would have two good panels and one cracked panel.

I do not see any solder joints that look like they need reflowed, but mine is not a trained eye.

[jetadm123]

Re: HP 1825 Display Black Power Light Green

Go ahead and swap in the logic/video card

[printone2]

Re: HP 1825 Display Black Power Light Green

Swap Inverter first.

Confirmed in known working lcd with cracked panel that the voltage going to the inverter was the same as measured in the dark lcd.

Swapped known good inverter into dark lcd. Power light stays on as usual and I get the same results as with the previous inverter, no CCFL.

Do you suspect I have bad tubes or a bad video card?

[retiredcaps]

Re: HP 1825 Display Black Power Light Green

Any suggestion on which board would be the first one to swap, or other suggested course of action?

Swap Inverter first.

[retiredcaps]

Re: HP 1825 Display Black Power Light Green

When I take into account the datasheet it becomes less clear. When I tested the 4416 according to the datasheet s1 is pin1 and g1 would be pin 4 from my reading, is this correct? That reading was 1. Is this making sense?

Sorry, my mistake. I cut and paste my "template" for testing mosfets. The first test is for FETs are thare 3 pins only.

Since your mosfet is more than 3 pins, just test S1-G1, S1-D1, G1-D1 combos. The datasheet will tell you what is S1 and D1. So if the datasheet says S1 is pin 1 and D1 is pin 4, that is correct.

If "1" is on the left hand side of the multimeter, that means it is out of range or infinite for that ohm scale. Proceed to finish the rest of the measurements.

[printone2]

Re: HP 1825 Display Black Power Light Green

I have one of the panels that lights up!! The LCD is smashed, but the CCFL light up. I have vertical lines and only a few square inches of normal looking video. This would indicate that I should be able to swap some parts between the monitors. Any suggestion on which board would be the first one to swap, or other suggested course of action?

[printone2]

Re: HP 1825 Display Black Power Light Green

Datasheet for 4416



Datasheet for 4435



If you have a manual range multimeter, set it to 200 ohms (two hundred). You can test a mosfet (Q, IC designation) "in circuit" by (power off and unplugged)

a) black on pin 1- red on pin 2 - record ohms .6 .6
b) black on pin 1- red on pin 3 - record ohms .6 .6
c) black on pin 2- red on pin 3 - record ohms .6 .6

If any ohm reading is less than 30 ohm you might have shorted mosfet. Remove from circuit and repeat the tests to verify.

Some mosfets are more than 3 pins. To test those, identify the part number and search for its datasheet. Once you find the datasheet, the pins will be designated source (S), gate (G), and drain (D). It will probably be documented as S1, S2, G1, G2, D1, D2.

Simply test

a) black on pin S1- red on pin G1 - record ohms
b) black on pin S1- red on pin D1 - record ohms
c) black on pin G1- red on pin D1 - record ohms

Repeat for the "2" pins. That is S2-G2, S2-D2, G2-D2.

The first step seems clear enough, using the small dipple as the pin 1 indicator I measured .6 on all of the pins listed on the 4416 MOSFET. I have not desoldered them, but tested in circuit with power off and power disconnected. When I take into account the datasheet it becomes less clear. When I tested the 4416 according to the datasheet s1 is pin1 and g1 would be pin 4 from my reading, is this correct? That reading was 1. Is this making sense?

[retiredcaps]

Re: HP 1825 Display Black Power Light Green

4416
4435

Datasheet for 4416



Datasheet for 4435



If you have a manual range multimeter, set it to 200 ohms (two hundred). You can test a mosfet (Q, IC designation) "in circuit" by (power off and unplugged)

a) black on pin 1- red on pin 2 - record ohms
b) black on pin 1- red on pin 3 - record ohms
c) black on pin 2- red on pin 3 - record ohms

If any ohm reading is less than 30 ohm you might have shorted mosfet. Remove from circuit and repeat the tests to verify.

Some mosfets are more than 3 pins. To test those, identify the part number and search for its datasheet. Once you find the datasheet, the pins will be designated source (S), gate (G), and drain (D). It will probably be documented as S1, S2, G1, G2, D1, D2.

Simply test

a) black on pin S1- red on pin G1 - record ohms
b) black on pin S1- red on pin D1 - record ohms
c) black on pin G1- red on pin D1 - record ohms

Repeat for the "2" pins. That is S2-G2, S2-D2, G2-D2.

[printone2]

Re: HP 1825 Display Black Power Light Green

Pin 1 11.9 (red jacket)
Pin 2 11.9 (all others gray jacket)
Pin 3 11.9
Pin 4 4.6
Pin 5 3.2
Pin 6 0.0
Pin 7 0.0
Pin 8 0.0

Now it makes sense the colored wire is just wire number 1 like on centronics or scsi cables and connectors. I just have not thought in those terms for a long while.

[jetadm123]

Re: HP 1825 Display Black Power Light Green

I see that I have three wires farthest from the fuse have -12v, the next has -8.5v, the fifth has -7.5v and then the sixth and seventh show no voltage and the last wire is ground.

The fuse tested good for continuity.



On the voltage regulator I have 5v on the lead marked "vin" and 2.5v on the center lead. The part # is CHN K310 LT25 Brand seems to be SI. That is the best I can make of the markings on the voltage regulator.

The 2.5V output looks good. Not sure why you're not at least getting an image using your flashlight.

[printone2]

Re: HP 1825 Display Black Power Light Green

These readings make more sense. pin 4 seems a bit low if it is supposed to be 5V DC, but let's assume it is good for now.

Above the 2 black transformers on the inverter board are four 8 pin ICs. What are the part numbers for each?

The two IC closest to the edge.
4416
(some mark maybe a zero with a slash or a trademark then) AG(delta)
W32B
These markings are very hard for me to see, but yes they are:

f P310J
fds
4435

[retiredcaps]

Re: HP 1825 Display Black Power Light Green

Pin 1 11.9 (red jacket)
Pin 2 11.9 (all others gray jacket)
Pin 3 11.9
Pin 4 4.6
Pin 5 3.2
Pin 6 0.0
Pin 7 0.0
Pin 8 0.0

These readings make more sense. pin 4 seems a bit low if it is supposed to be 5V DC, but let's assume it is good for now.

Above the 2 black transformers on the inverter board are four 8 pin ICs. What are the part numbers for each?