Impression 7LSP - No Video/Hum in Right Speaker

[browork]

I have an Impression 7LSP that is sick.

It has No Video and a Hum in the Right Speaker.

It truly has no video, you cannot see anything on the screen in a pitch black room (except the green/amber power light). The light does switch to amber after a few seconds and back to green when a computer is plugged in.

Power supply is good. It is external and reads 12.43V. The power supply is generic and labeled 12V 5A, a quick Google search shows this is the correct size power supply for this monitor.

The voltage regulator reads 3.27V on Pins 2/4, 4.95V on Pin 3, and 0V on pin 1 (Black lead on one of the screws). It is labeled L1084-33, so I think this means it is good.

All the caps look good, no bulging or leaking visible. They are labeled GSC.

From the pictures you can see the main board, LCD connector board and audio board. Unplugging the right speaker removes the hum, but still no picture. Unplugging the audio board altogether also removes the hum, but still no picture. I really did not think they were related.

I have not disassembled the LCD any further than you see in the pictures.

Any ideas where to go from here?

[momaka]

Re: Impression 7LSP - No Video/Hum in Right Speaker

While the GSC caps may not be the root cause of the issue, you should replace them as they are known to have a very high failure rate.
The problem you are describing might be an inverter issue. If you input a signal to the monitor and you hold a flashlight close to the screen, do you see a faint image where the flashlight is?
Also post a few pictures of the inverter board, if possible.

[browork]

Re: Impression 7LSP - No Video/Hum in Right Speaker

You are right and I am wrong. Late last night I had stated, "It truly has no video, you cannot see anything on the screen in a pitch black room," I now see this is not true.

Today when I plugged in the monitor, in the full light of day I see the screen, with no blacklight of course.

Is there any way we can test those backlights to make sure they are bad? Would both go out at once?

Attached are pictures of the inverter board. If I fix this I will probably remove the audio board and speakers to get rid of the hum. They are not needed anyway.

Edit: And yes I am searching the forums for how to test the backlight

[PlainBill]

Re: Impression 7LSP - No Video/Hum in Right Speaker

You are right and I am wrong. Late last night I had stated, "It truly has no video, you cannot see anything on the screen in a pitch black room," I now see this is not true.

Today when I plugged in the monitor, in the full light of day I see the screen, with no blacklight of course.

Is there any way we can test those backlights to make sure they are bad? Would both go out at once?

Attached are pictures of the inverter board. If I fix this I will probably remove the audio board and speakers to get rid of the hum. They are not needed anyway.

Edit: And yes I am searching the forums for how to test the backlight

I've marked up the picture of the bottom. First step, measure the resistance of the component marked 'Fuse?'. Also, is there any component identifier on the circuit board (F1, C201, R103), etc?

If it is labeled as a fuse, and it is intact, I have labeled the 5 pins from the main board. With power on, measure the voltage from each pin to Gnd.

If it is labeled as a fuse and it is open, I will need a better picture of the bottom of the board. This time don't use your flash. If the fuse is open, it would be a BAD IDEA to jumper across it with a piece of wire until you identify why it is blown.

PlainBill

[browork]

Re: Impression 7LSP - No Video/Hum in Right Speaker

The fuse is blown/open. The only thing I see on the fuse is a very faint 3. Is this a 3 amp fuse?

Attached are some better pictures. I still am using the flash, there is not enough natural light to not use it. Using an old photography trick of bouncing the light for a little better picture.

I see nothing on the board labeled C201, R103 or so on, but I will attack it with a magnifying glass once I find it.

[PlainBill]

Re: Impression 7LSP - No Video/Hum in Right Speaker

The fuse is blown/open. The only thing I see on the fuse is a very faint 3. Is this a 3 amp fuse?

Attached are some better pictures. I still am using the flash, there is not enough natural light to not use it. Using an old photography trick of bouncing the light for a little better picture.

I see nothing on the board labeled C201, R103 or so on, but I will attack it with a magnifying glass once I find it.

3 Amp seems likely. This is the same circuit used in Dell and Benq monitors, and should be repaired essentially the same way (part numbers will obviously be different).

Sometime you will have to explain about the bounce trick. The only way I have had any success is by turning off the flash and using a tripod.

I've had a lot of fun marking up the picture.

4 transistors circled in red. Check them for shorts. If any are shorted, ALL should be replaced. This may be all that has to be replaced (other than the fuse).

2 transistors and 2 diodes circled in blue. These might also be shorted, check them also. Replace if shorted.

4 sets of transformer pins circled in black. These MUST be resoldered. Failure to do so will most likely result in the replacement transistors shorting out and blowing the fuse.

I was unclear. There is no need to search for the allegorical components I mentioned.

PlainBill

[browork]

Re: Impression 7LSP - No Video/Hum in Right Speaker

Nothing on the board you circled is shorted. So does this mean I only need to replace the fuse? What do I look for in a replacement fuse.

Out of curiosity. When you say resolder the transformers. Do you mean taking them out of circuit and then putting them back in. Or just using a solder sucker to remove the solder and replace it with fresh/new solder?

I am not the best at explaining things, but here goes...

The flash thing is easy. Pick a light surface (white if possible) with a darker object (the darker your object is the better this will work), in my case I used the table. The flash focuses most of its force on the center of the picture, so set the object off center slightly. (In the picture you circled right below the board is where most of the flash is focused.) Also tilt your object between 15-30% grade to pickup the light from the surface. That is if the flash is built into the camera.

It is easier if the flash detaches from the camera. In that case focus the flash on a light surface, like a white piece of paper set at an angle to bounce the light off the paper to the object. Professional photographers use the ceiling or walls instead of paper. In outdoor settings I have seen large sheets used. It gives the object an indirect light.

As for a tripod. I think I might own one, but I certainly do not know where it is nor do I use it. If you ever had a class firing a weapon. Use the same principles when taking a picture.

Take several deep relaxing breaths prior to focusing on your target. Next, take a deep breath, exhale half the air and hold your breath and take the picture. Your body and more importantly the camera is stock still that second you hold your breath and take the picture. It takes practice, and some people like to fire or in this case take the picture exactly at the moment between breathes.

[PlainBill]

Re: Impression 7LSP - No Video/Hum in Right Speaker

Nothing on the board you circled is shorted. So does this mean I only need to replace the fuse? What do I look for in a replacement fuse.

Out of curiosity. When you say resolder the transformers. Do you mean taking them out of circuit and then putting them back in. Or just using a solder sucker to remove the solder and replace it with fresh/new solder?

I am not the best at explaining things, but here goes...

The flash thing is easy. Pick a light surface (white if possible) with a darker object (the darker your object is the better this will work), in my case I used the table. The flash focuses most of its force on the center of the picture, so set the object off center slightly. (In the picture you circled right below the board is where most of the flash is focused.) Also tilt your object between 15-30% grade to pickup the light from the surface. That is if the flash is built into the camera.

It is easier if the flash detaches from the camera. In that case focus the flash on a light surface, like a white piece of paper set at an angle to bounce the light off the paper to the object. Professional photographers use the ceiling or walls instead of paper. In outdoor settings I have seen large sheets used. It gives the object an indirect light.

As for a tripod. I think I might own one, but I certainly do not know where it is nor do I use it. If you ever had a class firing a weapon. Use the same principles when taking a picture.

Take several deep relaxing breaths prior to focusing on your target. Next, take a deep breath, exhale half the air and hold your breath and take the picture. Your body and more importantly the camera is stock still that second you hold your breath and take the picture. It takes practice, and some people like to fire or in this case take the picture exactly at the moment between breathes.

There are four ways to approach the fuse problem.

The first (best) is to use a current limited power supply and use that to provide power to the inverter. If you can successfully operate the inverter from the supply it is safe to replace the fuse. If the supply current limits, you have a chance of identifying the cause. The drawback is other than electronics repair professionals, few people have bench supply on hand.

The second is to attach a small 12 volt light bulb across the blown fuse. I have a 1157 automotive taillight I have rigged with three leads, one common, one low current (taillight), one high current (brake light / turn signal).

The third is to simply replace the fuse, either with an identical surface mount fuse, or with an equivalent rating picofuse or pigtail fuse.

The fourth is to jumper across the fuse with a piece of wire. If the fuse blew because of a dynamic load problem (shorted transformer) the failing components can be quickly identified by the clouds of smoke and acrid odor of burning plastic.

PlainBill

[browork]

Re: Impression 7LSP - No Video/Hum in Right Speaker

Since I like fire I went with option number 4... I also removed the transformers and resoldered them.

The LCD powered on fine and displays a screen fine. However, there is a buzzing noise coming from the circled part of the inverter board. I assume this is the transformer.

Any thoughts about this?


If it is the transformer, what part would I replace it with? Should I replace both of them?

Finally what type of fuse should I order? Picofuse brings up no results on digikey and pigtail fuse brings up LVSP0040HXP which I do not think is right.

[browork]

Re: Impression 7LSP - No Video/Hum in Right Speaker

As a side note I removed the transformer I circled. The hum is gone and the top half of the screen was dark (theres a shock). The part number of the transformer is SIT10153-1935 314D. I do not find this on Digikey or a Google search.

[PlainBill]

Re: Impression 7LSP - No Video/Hum in Right Speaker

As a side note I removed the transformer I circled. The hum is gone and the top half of the screen was dark (theres a shock). The part number of the transformer is SIT10153-1935 314D. I do not find this on Digikey or a Google search.

The question is: Is it the transformer, one of the CCFLs , or something else? Excessive load, improper drive, or shorted transformer could be causing this. The fact that the inverter worked without the transformer is disturbing. It suggests the design of the protection circuit is lacking.

The first step would be to see if there is enough slack in the wires to flip the inverter and plug the two CCFLs that were plugged into the buzzing transformer into the good transformer. If that end starts buzzing, the problem is in the CCFLs or the wiring.

If it doesn't, you have already removed one transformer; remove the second and replace it with the first. If the same transformer buzzes, it's likely time to look for a new transformer. Try searching on a partial number - often the number stamped on these includes a date or production code.

PlainBill

[browork]

Re: Impression 7LSP - No Video/Hum in Right Speaker

Labeling the transformers from left to right, 1 and 2.

2 was the one that was buzzing...

2 is also the one I removed... By the way how disturbing is this that the board still worked? Will it affect the usage when I get this one fixed?

All that you already know and I posted above...

I flipped the board and plugged the top ccfl into the bottom of the board. (bottom was to the left in the pictures)

No buzzing noise, no backlight on the bottom of the screen.

I then removed transformer number 1 and placed it in the number 2 position. Applying power gave me once again the top half the screen lit and no buzzing.

I than placed transformer number 2 in transformer number 1 spot. Upon applying power everything looks fine. No buzzing, no nothing. The display is great, in fact I am typing this on that display as we speak.

Now what does this mean?

I had removed and resolder the transformers before I soldered a wire across the fuse. Could I have messed up on resoldering? I didn't see anything while soldering, nor when removing (but I wasn't looking when I removing). I had also triple checked my solder job this time and see nothing.

The buzz happened the second I turned the LCD on before. This time it has been on for 20-30 minutes now and nothing. I will keep it running for a few more hours to keep testing.

Any other suggestions? Is it possible I just messed up soldering and that was the cause of the buzzing, or do you think it could be something more?

In the meantime I guess I need to find a replacement fuse.

Edit1: Fixed spelling errors
Edit2: Added photo
Edit3: Fixed more spelling errors

[browork]

Re: Impression 7LSP - No Video/Hum in Right Speaker

Would Digikey part 0402SFF300F/24CT-ND be OK for a replacement fuse? Or should I go with Digikey part P11368CT-ND?

Both are 24V, that is right, correct?

[PlainBill]

Re: Impression 7LSP - No Video/Hum in Right Speaker

Would Digikey part 0402SFF300F/24CT-ND be OK for a replacement fuse? Or should I go with Digikey part P11368CT-ND?

Both are 24V, that is right, correct?

Those two parts are functionally identical - just from different manufacturers. The only thing I would suggest is measuring the original and making sure the replacement is the same physical size (and rated for 3 amps, of course).

PlainBill

[browork]

Re: Impression 7LSP - No Video/Hum in Right Speaker

The size is right so the fuse is on order. Here is hoping that is the only problem, and I messed up soldering to give the transformer a buzz.

I have already removed the audio board, thought I will leave the speakers in the monitor (just not plugged into any thing). I don't use the built in speakers anyway.

[kc8adu]

Re: Impression 7LSP - No Video/Hum in Right Speaker

clean off the brown glue and repair any traces it ate.

[browork]

Re: Impression 7LSP - No Video/Hum in Right Speaker

PB, you were right to question the size of the fuse. Either I was seriously distracted when I looked for that part or I need to learn the difference between mm and inch.

The correct part, and the one that is the correct size and on order is DigiKey Part number SF-1206S300-2CT-ND

As a side note the monitor has now been running fine for the last five days with a wire replacing the fuse.

[PlainBill]

Re: Impression 7LSP - No Video/Hum in Right Speaker

PB, you were right to question the size of the fuse. Either I was seriously distracted when I looked for that part or I need to learn the difference between mm and inch.

The correct part, and the one that is the correct size and on order is DigiKey Part number SF-1206S300-2CT-ND

As a side note the monitor has now been running fine for the last five days with a wire replacing the fuse.

I speak from experience. Remember NASA's $125,000,000 Mars Climate Orbiter? Confusing between english and metric units caused it to crash. On a more personal level, I'm going to have to make a second trip to Lowes because I transposed two digits on the part number for some 'O' rings.

PlainBill

[browork]

Re: Impression 7LSP - No Video/Hum in Right Speaker

I replaced the fuse. It has been working great ever since. I will let it run a few more days before I call it fixed, but it looks like the fuse might have been the only issue.

[PlainBill]

Re: Impression 7LSP - No Video/Hum in Right Speaker

I replaced the fuse. It has been working great ever since. I will let it run a few more days before I call it fixed, but it looks like the fuse might have been the only issue.

D**n!!! When I replace the fuse the most expensive IC on the board shorts and blows half a dozen lands on the board.

So who do you like to win the World Series?

PlainBill