HP L1925 Video Input Logic Board won't power on

[maverick530]

I have an HP L1925 LCD monitor that has a Video Input Logic Board (00.59802.B01 REV.B) with a pixelworks PW131A-20Q chip that won't power on. I verified all the other parts to the monitor work with a known-good logic board. It looks as though the power from the PSU of the monitor flows through this board and then onto the power inverter to power the display.

My biggest question is, see the huge green capacitor that says "TAICON" on it? (Left of the pixel works chip) Visually, it has a lot of gewy crud all over it-- is that putty just to hold the capacitor in place, or is it actually blown? Do capacitors blow like that?

What's more, could that be the cause of the blowout burned mark on the bottom left of the back of the board, directly opposite the AC 1501-50 03013 chip (that has 5 pinouts)? My guess is that chip blew, but WHY did it blow? Would replacing this chip just cause it to blow out again?

[EGuevarae]

Re: HP L1925 Video Input Logic Board won't power on

What's more, could that be the cause of the blowout burned mark on the bottom left of the back of the board, directly opposite the AC 1501-50 03013 chip (that has 5 pinouts)? My guess is that chip blew, but WHY did it blow? Would replacing this chip just cause it to blow out again?

Just make sure that that 1501-50 ( I guess that is the number on the chip, 'cause I coudn't figure out anything from the pic, as it is too dark) does not end like this one I tried to remove from a dead board (I have a eMachines E15T3g with that chip shot)
And as a reference take the board from your other 1925 thread. It does not look like the one on this one. You can change the cap if in doubt, just to test (either for the one in the other board or a completely different one). Also, look up the chip in alldatasheet.com and see if the IC is shot or not. Mine is short from pin 3 - GND- to 5. The other one (the "naked", from the pic) was not.

Also, what brand/series are the other caps?

[maverick530]

Re: HP L1925 Video Input Logic Board won't power on

I found the datasheet for the 1501-50 chip (attached). Can I
test this on-board or do I have to desolder it first in order to properly
test it with a multimeter?

Also, is it even possible to remove these chips? What if they are glued on (see previous post)? Does anybody know of a good way to unseat these chips for transplant onto other boards?

[maverick530]

Re: HP L1925 Video Input Logic Board won't power on

Unlike my other board, this one is 100% TAICON caps.

[EGuevarae]

Re: HP L1925 Video Input Logic Board won't power on

Replace them.
Look at the bad cap manufacturer list here and you will find them there.

[maverick530]

Re: HP L1925 Video Input Logic Board won't power on

Ok, I just replaced the 4 suspected "bad" caps, and each circled tap still registers as shorted. I tested the "bad" caps once out, and they all seem to hold charges. So, it turns out that it wasn't a cap problem at all, and I'm still left with a bad monitor that won't accept a signal. What else can I try?

[EGuevarae]

Re: HP L1925 Video Input Logic Board won't power on

Ok, I just replaced the 4 suspected "bad" caps, and each circled tap still registers as shorted. I tested the "bad" caps once out, and they all seem to hold charges. So, it turns out that it wasn't a cap problem at all, and I'm still left with a bad monitor that won't accept a signal. What else can I try?

Have you checked the 1501-50 chip? It could have gone bad because of the caps or a surge in the PSU or just because he wanted to . The E15T3g I was messing with has this IC bad, and everything else seems to be OK. The monitor is dead because of that IC.
How I found out it was bad (why I tested it)? I started following the (+) pin from the DC in (in your case, the connector from the PSU) and traced the voltage up to that point. It reached the IC and it disappeared. Then I took the number on the IC, found out what it was, and tested.Shorted on 3-5, and then I checked the (now naked and useless) other one, and they didn't do the same, so I concluded that t was bad. Apply power to the board, and follow the V until it is lost. See if it varies along the path (I've seen 12, 5 & 3.3 on logic boards. Dunno if they are more Voltages used in that cards). If you follow a 12v path and end up suddenly with 17 or 7v, then something is wrong.
Maybe it is obvious for experienced electronics people but It is what I do and so far, it has helped me on many cases, monitors and not monitors....
Anything you need, just email me. PM me or post here. Glad to give help.
Eduardo

[PCBONEZ]

Re: HP L1925 Video Input Logic Board won't power on

I tested the "bad" caps once out, and they all seem to hold charges. So, it turns out that it wasn't a cap problem at all,

That doesn't tell you anything about the caps.

[maverick530]

Re: HP L1925 Video Input Logic Board won't power on

Ok, I just replaced the 4 suspected "bad" caps, and each circled tap still registers as shorted. I tested the "bad" caps once out, and they all seem to hold charges. So, it turns out that it wasn't a cap problem at all, and I'm still left with a bad monitor that won't accept a signal. What else can I try?

Sorry this was mis-posted to the wrong thread. How do I remove this post? I can't find a link ANYWHERE.

[maverick530]

Re: HP L1925 Video Input Logic Board won't power on

That doesn't tell you anything about the caps.

Can you expound on this? How can you tell whether or not a cap is bad? What DMM settings do you use?

[maverick530]

Re: HP L1925 Video Input Logic Board won't power on

I desoldered the old IC (1501) and ripped a good one from another board that I had (not wanting to spend the $4.50 digitech was going to charge me, so I took the PCB and all from the other board, I'll have to show you a pic). I turned the monitor on, and still nothing. No green light, no picture, nothing. I think I might have ripped up where the IC contacts the board (PCB). I can't tell where on the PCB the IC's contacts are connecting to (probably some inner layer of the PCB) so I think I killed that board. Oh well, no guts, no glory. In this case, I all I'm left with is guts.

BTW, I did also replace the suspected bad Green 1000uF 16v TAICON Capacitor with the donor board's cap. Out of the board, the suspected bad one still seemed to charge so now I'm thinking the IC was the only thing blown.

My advice next time, is to just spend the money and get a new one, if it's suspected bad. Don't try and use a donor board to give you one. It is impossible to remove (as demonstrated in post #2) and you will not only ruin the bad board you took it from, but you may also ruin the board you're trying to fix in the process.

[EGuevarae]

Re: HP L1925 Video Input Logic Board won't power on

My advice next time, is to just spend the money and get a new one, if it's suspected bad. Don't try and use a donor board to give you one. It is impossible to remove (as demonstrated in post #2) and you will not only ruin the bad board you took it from, but you may also ruin the board you're trying to fix in the process.

I managed to do this finally (not that IC, another one, and not 5 pins, 8). It requires a fine tip soldering iron, lots of patience and a steady hand. But it can be done.

I desoldered the old IC (1501) and ripped a good one from another board that I had (not wanting to spend the $4.50 digitech was going to charge me, so I took the PCB and all from the other board, I'll have to show you a pic). I turned the monitor on, and still nothing. No green light, no picture, nothing. I think I might have ripped up where the IC contacts the board (PCB). I can't tell where on the PCB the IC's contacts are connecting to (probably some inner layer of the PCB) so I think I killed that board. Oh well, no guts, no glory. In this case, I all I'm left with is guts.

Well, anyway, you must learn how to change them properly, because even if you get a new one, you still have to remove the dead/bad one and put in the new (you'll just save one removal - the removal of the good IC from the donor card)

BTW, I did also replace the suspected bad Green 1000uF 16v TAICON Capacitor with the donor board's cap. Out of the board, the suspected bad one still seemed to charge so now I'm thinking the IC was the only thing blown.

Bad caps can cause it to malfunction, or kill something else. If you get your hands on a board or PSU and it has bad caps on it, if you think it is worth (for me a 19" LCD from HP is worth ...), go and recap it. Then start checking something else. With time and practice (experience ...) you will learn how to recognize problems either related to caps or not....

[EGuevarae]

Re: HP L1925 Video Input Logic Board won't power on

Can you expound on this? How can you tell whether or not a cap is bad? What DMM settings do you use?

Well. I use an analog Multimeter to see how they charge/discharge. It is not a sure way to spot a bad cap (even if they charge, the ESR might be high), but it helps to spot open, short and several caps that don't fully charge (leaky).
I guess the only sure method is either a capacitance meter or an ESR meter.

[maverick530]

Re: HP L1925 Video Input Logic Board won't power on

I desoldered the old IC (1501) and ripped a good one from another board that I had (not wanting to spend the $4.50 digitech was going to charge me, so I took the PCB and all from the other board, I'll have to show you a pic). I turned the monitor on, and still nothing. No green light, no picture, nothing. I think I might have ripped up where the IC contacts the board (PCB). I can't tell where on the PCB the IC's contacts are connecting to (probably some inner layer of the PCB) so I think I killed that board. Oh well, no guts, no glory. In this case, I all I'm left with is guts.

BTW, I did also replace the suspected bad Green 1000uF 16v TAICON Capacitor with the donor board's cap. Out of the board, the suspected bad one still seemed to charge so now I'm thinking the IC was the only thing blown.

My advice next time, is to just spend the money and get a new one, if it's suspected bad. Don't try and use a donor board to give you one. It is impossible to remove (as demonstrated in post #2) and you will not only ruin the bad board you took it from, but you may also ruin the board you're trying to fix in the process.

Here is the pic of my work, as you can see, it's poorly soldered onto the board where it needs to be. I don't think there's any saving this one.

[EGuevarae]

Re: HP L1925 Video Input Logic Board won't power on

Here is the pic of my work, as you can see, it's poorly soldered onto the board where it needs to be. I don't think there's any saving this one.

I can't figure much from the pics (dark), but please tell me that you didn't rip the donor IC WITH THE PIECE OF BOARD STILL ATTACHED and soldered it on the board WITHOUT TAKING THE OTHER OFF.

[maverick530]

Re: HP L1925 Video Input Logic Board won't power on

I can't figure much from the pics (dark), but please tell me that you didn't rip the donor IC WITH THE PIECE OF BOARD STILL ATTACHED and soldered it on the board WITHOUT TAKING THE OTHER OFF.

Yep, I ripped the IC off of the other board with the board still attached! Why not? The IC doesn't need to be grounded, and as you saw, it is near impossible to remove from the board. So I just cut around it and it probably would have worked perfectly if I knew how to bend up the pins where the old IC is connected to the board without stripping the pins entirely off of the board (I know now how to do it, you have to hold the pin down with a flat-head screw driver, applying pressure onto the board where it is connected while bending the other sawed-off ends up at the same time).

If I ever get another board with this same problem, I'll try again and repost, but I'm out of luck for now.

[EGuevarae]

Re: HP L1925 Video Input Logic Board won't power on

Well. What can I say ....
A very unorthodox way to fix an LCD, but if you learned something in the process.

[jpdoe]

Re: HP L1925 Video Input Logic Board won't power on

Hi, eguevarae

>>> Well. I use an analog Multimeter to see how they charge/discharge.

You do it in-circuit or out of circuit?

[EGuevarae]

Re: HP L1925 Video Input Logic Board won't power on

Hi, eguevarae
>>> Well. I use an analog Multimeter to see how they charge/discharge.
You do it in-circuit or out of circuit?

Out of circuit.

[Bobdee]

Re: HP L1925 Video Input Logic Board won't power on

Hello Eduardo

Have you checked the 1501-50 chip? It could have gone bad because of the caps or a surge in the PSU or just because he wanted to . The E15T3g I was messing with has this IC bad, and everything else seems to be OK. The monitor is dead because of that IC.
How I found out it was bad (why I tested it)? I started following the (+) pin from the DC in (in your case, the connector from the PSU) and traced the voltage up to that point. It reached the IC and it disappeared. Then I took the number on the IC, found out what it was, and tested.Shorted on 3-5, and then I checked the (now naked and useless) other one, and they didn't do the same, so I concluded that t was bad.
Eduardo

I have a question for you as I am in a quandry, I will explain,
I have 2 boards on the desk in front of me now, both dells, E173fpf + E153fpf.
Both monitors were totaly dead before removing the said boards, they are the 3 in 1 type inverter + psu + video on the 1 board , they are very similar to each other, both have ic like your 1501-50, only these are 1506-50,
when you compare datasheets they are the same to me, my datasheet is



Same pinout + block diagram, the 2 ic of mine have continuity between 3 and 5, I have had no reason to suspect these 2 ICs , no discolouration on the boards,they both look in perfect condition,the 17'' I cannot see anything wrong with it, but the 15'' has burnt out current resistor on it, on the PSU side of it, between the mosfet source and the PWM controller so I believe this is the problem on this board, now to question,

Is it possible that your conclusion was wrong on your IC about it being bad ???

I read all your post and I know your capadility is very good, but I ask because the coincidence of them all being bad on diffrent boards is strange, and if you are right then I have a couple of hard tasks on my hands that I am not looking forward to, so I am hoping that is not so, I wait for your reply,
many thxs
bob