HP 1825 Display Black Power Light Green

[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

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

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?

[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

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.

[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

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.

[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 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.

[jetadm123]

Re: HP 1825 Display Black Power Light Green

Great to hear that! Good work!

[printone2]

Re: HP 1825 Display Black Power Light Green

Great to hear that! Good work!

Well I am not quite done yet. It looks like two of the inverters are bad, but I do have one good one. I have swapped inverters between two of the panels and determined that the lamps, power supplies and image cards are good in all three panels, but I have two bad inverters. What is the easiest way to compare the bad inverters to the good one?

[jetadm123]

Re: HP 1825 Display Black Power Light Green

Well I am not quite done yet. It looks like two of the inverters are bad, but I do have one good one. I have swapped inverters between two of the panels and determined that the lamps, power supplies and image cards are good in all three panels, but I have two bad inverters. What is the easiest way to compare the bad inverters to the good one?

1) verify the fuse F1 is good.

2) on your photo of the inverter: looking at the top there are two 8-pin surface mount chips on the outside of each purple cap. I believe these are mosfets (possibly duo mosfets) that generate the sine wave for amplification by the inverter transformer to power the CCFL's. These should be checked for shorts using your DMM.

3) if the mosfets check good, then you can always try changing the two purple caps.

[printone2]

Re: HP 1825 Display Black Power Light Green

The only fuse I see is the one near the power plug on the power supply and they check out as good. I will do some research on how to test mosfets.

[printone2]

Re: HP 1825 Display Black Power Light Green

1) verify the fuse F1 is good.

2) on your photo of the inverter: looking at the top there are two 8-pin surface mount chips on the outside of each purple cap. I believe these are mosfets (possibly duo mosfets) that generate the sine wave for amplification by the inverter transformer to power the CCFL's. These should be checked for shorts using your DMM.

3) if the mosfets check good, then you can always try changing the two purple caps.

I found the F1 fuse on the inverter board and yes they are blown on both of the bad inverter boards and good on the functioning board. Now what caused it? I still have to check the mosfets.

[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
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.

Here are the readings from the Mosfets: (">" represents overlimit, ohms
set manually at 200 ohms)

4416 Board1 Board 2 Board 3
(1of2) (working)

S-G 153 199 147

S-D > 162 >

G-D > > >

4416 Board1 Board 2 Board 3
(2of2) (working)

S-G > 167 >

S-D > 132 >

G-D > 131 >


4435 Board1 Board 2 Board 3
(1of2) (working)

S-G > 142 >

S-D 84 111 >

G-D > 191 >

4435 Board1 Board 2 Board 3
(2of2) (working)

S-G > 134 186

S-D ? ? ?

G-D > > >

And the fuse on the inverter labeled F1 is not good on the two inverter boards that are not working.

Thanks.

[jetadm123]

Re: HP 1825 Display Black Power Light Green

Here are the readings from the Mosfets: (">" represents overlimit, ohms
set manually at 200 ohms)

4416 Board1 Board 2 Board 3
(1of2) (working)

S-G 153 199 147

S-D > 162 >

G-D > > >

4416 Board1 Board 2 Board 3
(2of2) (working)

S-G > 167 >

S-D > 132 >

G-D > 131 >


4435 Board1 Board 2 Board 3
(1of2) (working)

S-G > 142 >

S-D 84 111 >

G-D > 191 >

4435 Board1 Board 2 Board 3
(2of2) (working)

S-G > 134 186

S-D ? ? ?

G-D > > >

And the fuse on the inverter labeled F1 is not good on the two inverter boards that are not working.

Thanks.

Looks like the spacing you used for each column didn't come out as planned. Some of the wording came out under the wrong column and added some confusion. I would like to verify that when your meter reads over limit, it means the reading is over 200ohms? Also, on the last reading S-D of the 4435, what does the ? mark mean?

[printone2]

Re: HP 1825 Display Black Power Light Green

I found the F1 fuse on the inverter board and yes they are blown on both of the bad inverter boards and good on the functioning board. Now what caused it? I still have to check the mosfets.

All the work to make the columns line up was worthless. The "?" meant that I did not measure that parameter. The first reading in each line represents board 1, then board 2 and finally 3. Board #2 is the one that is working.

Yes the overlimit readings are in excess of 200ohms.

[jetadm123]

Re: HP 1825 Display Black Power Light Green

All the work to make the columns line up was worthless. The "?" meant that I did not measure that parameter. The first reading in each line represents board 1, then board 2 and finally 3. Board #2 is the one that is working.

Yes the overlimit readings are in excess of 200ohms.

Doesn't look like anything is shorted assuming that 4435 with the ? marks are good.


Here's what I suggest: take one of the "bad" inverter boards and remove fuse F1. Instead of replacing that fuse with another SMD fuse (they are a little pricey) go to Radio Shack and purchase a cheap fuse holder for glass type cartridge fuses. Not sure what amperage fuse to purchase. Go ahead and replace the 2 purple caps. If it doesn't solve the problem and blows the fuse again, at least you'll be able to use much cheaper glass fuses until the problem is resolved. Once the problem is solved, then go ahead and purchase the correct SMD fuse.

[printone2]

Re: HP 1825 Display Black Power Light Green

Doesn't look like anything is shorted assuming that 4435 with the ? marks are good.


Here's what I suggest: take one of the "bad" inverter boards and remove fuse F1. Instead of replacing that fuse with another SMD fuse (they are a little pricey) go to Radio Shack and purchase a cheap fuse holder for glass type cartridge fuses. Not sure what amperage fuse to purchase. Go ahead and replace the 2 purple caps. If it doesn't solve the problem and blows the fuse again, at least you'll be able to use much cheaper glass fuses until the problem is resolved. Once the problem is solved, then go ahead and purchase the correct SMD fuse.

I did a poor job of laying out the mosfet readings. The readings I took are pretty different on the second board (functional board than the other two), but I do not know what normal readings should look like. On the 4416 the working lcd has readings on most leads tested, but the non working panels have over limit readings on most leads. I will read some more.

The small purple caps are sanyo brand, so a better quality than the capxons populated on the rest of the boards from what I am reading.

Thanks

[jetadm123]

Re: HP 1825 Display Black Power Light Green

I did a poor job of laying out the mosfet readings. The readings I took are pretty different on the second board (functional board than the other two), but I do not know what normal readings should look like. On the 4416 the working lcd has readings on most leads tested, but the non working panels have over limit readings on most leads. I will read some more.

The small purple caps are sanyo brand, so a better quality than the capxons populated on the rest of the boards from what I am reading.

Thanks

The purpose of the resistance check is for one purpose only: to locate a short between the S,D or G pins of the mosfet. Since mosfets are made differently than a BJT transistor, you cannot strictly use a resistance test to verify that a mosfet is good. However, in the case of a mosfet failing on an inverter, they generally will short out and that's what we're looking for. Therefore, don't expect to find a "normal" reading resistance wise. So, if you don't see a short using the suggested test methods, then move onward.