HP 1825 Display Black Power Light Green

[printone2]

Re: HP 1825 Display Black Power Light Green

If these are good lamps, I just leave them in their lcd housing and stretch the cables from the other monitor for testing. You don't need to build anything fancy.

Thanks.

[retiredcaps]

Re: HP 1825 Display Black Power Light Green

How can I use the good lamps to test problems on other panels?

If these are good lamps, I just leave them in their lcd housing and stretch the cables from the other monitor for testing. You don't need to build anything fancy.

[printone2]

Re: HP 1825 Display Black Power Light Green

PROBABLY a 5A fast blow. F= fast blow T=5Amp

PlainBill

I replaced the smd fuse with SF-1206F500-2CT-ND from Digi-Key, it is a 5 amp fast smd 1206. That along with the 22uf 25v caps on the inverter made the difference. I recapped the image card and the power supply with samxon's from badcaps.net and now two of the three panels appear to work fine. The third panel has a smashed screen, but the image and power boards are fine.

How can I use the good lamps to test problems on other panels? I seem to have read about a kit to test lamps with. Where are plans for such a kit?
Thanks everyone.

[PlainBill]

Re: HP 1825 Display Black Power Light Green

The good fuse at F1 has the letters "FT" on it.

PROBABLY a 5A fast blow. F= fast blow T=5Amp

PlainBill

[printone2]

Re: HP 1825 Display Black Power Light Green

A good picture of F1 would help. it's probably in the 2-4 amp range, but most SMD fuses have a single letter on them which identifies the rating.

PlainBill

The good fuse at F1 has the letters "FT" on it.

[PlainBill]

Re: HP 1825 Display Black Power Light Green

I have one fuse on one inverter board that is good, but how do I tell what a replacement fuse should be for two boards that the bad caps caused the fuse to blow? The fuse is located at F1 on the inverter and is an smd. I have put a temporary glass 4amp fuse in place of the blown fuse. It seems to work fine, but I am not at all sure if that is a reasonable value for the replacement. I would like to have a few standard fuses on hand. Can someone suggest some normal ones to keep around as spares as well as suggest what might be reasonable for location F1?

A good picture of F1 would help. it's probably in the 2-4 amp range, but most SMD fuses have a single letter on them which identifies the rating.

PlainBill

[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.

I have one fuse on one inverter board that is good, but how do I tell what a replacement fuse should be for two boards that the bad caps caused the fuse to blow? The fuse is located at F1 on the inverter and is an smd. I have put a temporary glass 4amp fuse in place of the blown fuse. It seems to work fine, but I am not at all sure if that is a reasonable value for the replacement. I would like to have a few standard fuses on hand. Can someone suggest some normal ones to keep around as spares as well as suggest what might be reasonable for location F1?

[printone2]

Re: HP 1825 Display Black Power Light Green

When replacing my caps I see that I made a mistake in measuring the height of the caps. It should read that the 470uf 25v caps are 10mm wide and 16 mm high. The two caps on the inverter are 7 mm wide and 5 mm high and 22uf 25v. Both of these caps were bad and appear to be the reason for the bad smd fuse at location F1.

After replacing these items with some temporary caps and a temp fuse the panel lights up.

Thanks again for everyone's help.

[printone2]

Re: HP 1825 Display Black Power Light Green

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.

Now here is a newbie conclusion, that as long as there is some resistance then it has not shorted out, so only a low ohm reading would indicate a bad mosfet?

[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.

[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

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

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

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

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.

[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

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.

[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

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

Great to hear that! Good work!