HP LP1965 - Power light green, no image

[badandy]

Re: HP LP1965 - Power light green, no image

Check the 4 fuses that jetadm123 circled. If they are good, check fuse F5 on the panel board and also measure voltage between ground and the test point labeled "AVDD1". Should be around 10~13v I think. Post back what results you get.

Fuse F5 is open on the panel board.

I tested between avdd1 and gnd1 and have zero voltage.
I am assuming that gnd1 is a good ground for testing.

I have attached a pic of the part of the board where gnd1 is and circled it.

Is F5 the culprit or did something else cause it to blow?

[momaka]

Re: HP LP1965 - Power light green, no image

I tested between avdd1 and gnd1 and have zero voltage.
I am assuming that gnd1 is a good ground for testing.


I have attached a pic of the part of the board where gnd1 is and circled it.

Not sure if gnd1 is a proper ground. However, the exposed copper areas near the screw holes definitely are, so use those instead. It should be easier too.

Fuse F5 is open on the panel board.
...
Is F5 the culprit or did something else cause it to blow?

Depends. Most of the time, an overload on the main boosted voltage rail ("AVDD1") will cause the fuse to blow. This usually happens when one of the filtering ceramic capacitors on it becomes shorted. I had one monitor do that.

So with that said, check resistance between Avdd1 and ground (i.e. exposed copper area near screw holes). Use the lowest ohm setting on your multimeter if it's manual range. Post back what results you get.

[badandy]

Re: HP LP1965 - Power light green, no image

Not sure if gnd1 is a proper ground. However, the exposed copper areas near the screw holes definitely are, so use those instead. It should be easier too.


Depends. Most of the time, an overload on the main boosted voltage rail ("AVDD1") will cause the fuse to blow. This usually happens when one of the filtering ceramic capacitors on it becomes shorted. I had one monitor do that.

So with that said, check resistance between Avdd1 and ground (i.e. exposed copper area near screw holes). Use the lowest ohm setting on your multimeter if it's manual range. Post back what results you get.

I checked between avdd1 and the closest screwpad, the initial resistance is 1 ohm and after a second or two it falls to .8 ohms.

[momaka]

Re: HP LP1965 - Power light green, no image

I checked between avdd1 and the closest screwpad, the initial resistance is 1 ohm and after a second or two it falls to .8 ohms.

That means AVdd1 is indeed shorted. The most likely culprit will be one of the small ceramic SMT capacitors on that rail - i.e. C11, C12, C13, C15, and possibly C241. It could also be that diode D10 is shorted and the whole 5v rail is shorted, but this is very unlikely. Nonetheless, this should be checked - basically measure resistance between ground and one of the pads of the inductor (it doesn't matter which side of the inductor you chose). If you get more than 40 ohms (steady reading), then diode D10 and the 5v rail are fine. However, if you do get less than 40 Ohms, let me know.

Assuming you did get more than 40 Ohms (the more likely case), then we need to find what is causing the short circuit on AVdd1. Like I mentioned above, it's probably one of the small ceramic capacitors on AVdd1.

AVdd1 starts at the cathode of D10 (the side marked with a white stripe and the letter "K") and continues through two 0 Ohm jumper resistors, R15 and R16.
You can start by removing R15, then measure resistance between ground and the cathode of D10.
- If you don't get a short circuit (i.e. same reading like you did when you measured resistance between ground and AVdd1), the problem is somewhere after R15, most likely C15 or possibly C241 if C241 is connected together with C15.
- If you do get a short circuit, remove R16, then measure resistance again between ground and cathode of D10. If short circuit is gone, remove C11 and check it - if it's not shorted, let me know. Otherwise if the short circuit is still present between ground and cathode of D10, remove C12 and C13, then check them with your multimeter.

Let me know how it goes.
Also, try not to damage any of the ceramic capacitors when you remove them - those that are not shorted can be put back in the circuit afterwards.

[badandy]

Re: HP LP1965 - Power light green, no image

Momaka,

I tested D10, the cathode to ground measures 1-.08 ohms

the anode to ground measured a steady 1364 ohms.

I figured I would run these readings by you first before I attempt to
remove the resistors or capacitors.

Thanks again for all your help with this!

[momaka]

Re: HP LP1965 - Power light green, no image

No problem .

Momaka,

I tested D10, the cathode to ground measures 1-.08 ohms

the anode to ground measured a steady 1364 ohms.

Those reading confirm that D10 and the 5v rail are fine. That means only AVdd1 is shorted, so unfortunately you will have to remove those resistors and capacitors I mentioned above.

Don't worry, though, it's not as hard as it seems. The traces on the board are not that easy to destroy. Just make sure your soldering iron is nice and very hot.
The ceramic capacitors may be a bit more tricky to remove, but take your time with them. Heat them up from one side and then the other multiple times and they should come off without damage.

[PlainBill]

Re: HP LP1965 - Power light green, no image

No problem .


Those reading confirm that D10 and the 5v rail are fine. That means only AVdd1 is shorted, so unfortunately you will have to remove those resistors and capacitors I mentioned above.

Don't worry, though, it's not as hard as it seems. The traces on the board are not that easy to destroy. Just make sure your soldering iron is nice and very hot.
The ceramic capacitors may be a bit more tricky to remove, but take your time with them. Heat them up from one side and then the other multiple times and they should come off without damage.

Or use Chip-Quick.

PlainBill

[Diablo_Rojo]

Re: HP LP1965

Hope that it is ok for me to jump on the end of this thread with a different problem with the same model monitor. I have a monitor that will not power on. I measured voltage on correct on power board but on the video board I measured 5V in and only .5V out on the AIC1185 33 PM. I pulled up the output leg on the regulator and still measured the same. Convinced that the regulator was bad I ordered http://search.digikey.com/scripts/Dk...=497-1222-1-ND this 497-1222-1-ND from digi-key. After the replacement I still got the same output. I pulled the new regulator off and measured 138 ohm from input to ground. I don't know if a)I got a bad component, b) what I ordered was not a compatible substitution (drop out voltage is higher) or, c) something is causing it to fail (I suspect 100uf cap on output). Any guidance is greatly appreciated.

[PlainBill]

Re: HP LP1965

Hope that it is ok for me to jump on the end of this thread with a different problem with the same model monitor. I have a monitor that will not power on. I measured voltage on correct on power board but on the video board I measured 5V in and only .5V out on the AIC1185 33 PM. I pulled up the output leg on the regulator and still measured the same. Convinced that the regulator was bad I ordered http://search.digikey.com/scripts/Dk...=497-1222-1-ND this 497-1222-1-ND from digi-key. After the replacement I still got the same output. I pulled the new regulator off and measured 138 ohm from input to ground. I don't know if a)I got a bad component, b) what I ordered was not a compatible substitution (drop out voltage is higher) or, c) something is causing it to fail (I suspect 100uf cap on output). Any guidance is greatly appreciated.

Well, since it was an 'extension' rather than a 'hijack' of the thread, it's OK.

Your events pose a pretty problem. Ordinarily I expect replacement parts to be good, but experience shows that's not always the case. The problem is explaining how the replacement part could have been damaged in circuit. Usually the design has both current and temperature protection. Yes, the dropout voltage is higher, but still (barely) within operating margins.

How did you remove the old regulator, and mount the new one?

PlainBill

[jetadm123]

Re: HP LP1965

Hope that it is ok for me to jump on the end of this thread with a different problem with the same model monitor. I have a monitor that will not power on. I measured voltage on correct on power board but on the video board I measured 5V in and only .5V out on the AIC1185 33 PM. I pulled up the output leg on the regulator and still measured the same. Convinced that the regulator was bad I ordered http://search.digikey.com/scripts/Dk...=497-1222-1-ND this 497-1222-1-ND from digi-key. After the replacement I still got the same output. I pulled the new regulator off and measured 138 ohm from input to ground. I don't know if a)I got a bad component, b) what I ordered was not a compatible substitution (drop out voltage is higher) or, c) something is causing it to fail (I suspect 100uf cap on output). Any guidance is greatly appreciated.

You mentioned that you pulled the middle leg up and measured the same output. Looking at the ST spec sheet, the middle leg is internally connected to the metal tab in the back of the regulator, which is soldered directly to the pc board. Correct? So, lifting up the middle leg to test the voltage does no good, since the output is still connected to the load via the middle tab.

If you still have the old regulator, try inputing 6V or 9V from an external battery and measure for the 3.3V. If you get 3.3V, then you may have a short on the card. If you still get the .5V, then PlainBill's suggestions about removal/install may come into play.

[Diablo_Rojo]

Re: HP LP1965 - Power light green, no image

Thank you so much for the responses. Sorry if I did not make it clear that I pulled up the bottom right leg not the middle leg. I guess I should have added a d) bad soldering skills, to my original post. I use a Weller 25W iron and perhaps I overheated. Thank you for the brilliant idea of testing the old regulator with a battery. Using a 9V battery I was able to measure 3.3V on the output! I am not sure how to proceed from here.

[jetadm123]

Re: HP LP1965 - Power light green, no image

Thank you so much for the responses. Sorry if I did not make it clear that I pulled up the bottom right leg not the middle leg. I guess I should have added a d) bad soldering skills, to my original post. I use a Weller 25W iron and perhaps I overheated. Thank you for the brilliant idea of testing the old regulator with a battery. Using a 9V battery I was able to measure 3.3V on the output! I am not sure how to proceed from here.

Actually, the bottom right leg is for the input voltage. You say that you pulled up the output leg, which I assumed to be the middle leg. Please review the ST data sheet, so that we're all on the same page. And compare the ST datasheet to the AIC datasheet to verify that the ground, input and output legs correspond to each other.

Post some good, clear, focused pictures of your entire logic board.

Once you've verified the datasheet, try measuring across the 100uf cap for a short. It's not an accurate test, but worth a try.

[Diablo_Rojo]

Re: HP LP1965 - Power light green, no image

Well, it has come to my attention that the LD108533 http://www.st.com/internet/com/TECHN...CD00001883.pdf does not have the same pin configuration as my original AIC1185-33 http://www.google.com/url?sa=t&sourc...qr15Kg&cad=rja. I should pay better attention. Thank you for showing me the error of my way. I am having great difficulty finding a replacement at dig-key. I still believe the original regulator is faulty as I measured such a low voltage on the output pin(bottom right on the AIC1185) with it lifted from the pad.

[snorlin]

Re: HP LP1965 - Power light green, no image

Hello,
I just worked on a LP1965 with a video problem (distorted/wavy lines). I found C414, a 10u 50v cap on the video board that was bad. It's right in line with Pin 1 of the ribbon connector to the display panel. Hope that helps someone. Love this site.