Mag LT916s Model 900p 19" LCD dropping like flies

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Okay, I'm a newbie on this forum and I'm sure you all wish this thread would go away, but this is the main reason why I signed into this forum:

I too, have the problem of my Mag LT916s monitor turning off after 2 seconds.

I replaced all 6 of the 470uf 25v caps as well as the 220uf 25v cap and I still have the same problem. Even though none of the caps exhibited the tell-tale bulge and/or leakage. I thought this to be a cost-effective place to start. All the caps were soldered in properly without any shorting.

I have looked through the threads on this subject, albeit more like "skimming" through and I would like to know what is my next step?

I also want to thank all of you for your help in this matter. This is a great forum!

Mike

This sounds like the 'two seconds to black' problem. I've discussed this extensively. A quick search here will find many of the posts. I suggest as a first step you compare the resistance of the secondaries of the inverter transformers. An open or shorted secondary is one of many possible causes. Posting a picture of the back of the inverter would also allow me to make suggestions.

PlainBill

[mjbattmer]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Plainbill, thanks for replying.

Now, an update: After letting the monitor set overnight in a cooler place, I turned it on and it now stays on for about 8 seconds then the screen flickers and slowly shuts down around the eleven second mark. I shined a bright light on the screen and I can see faint images.

Cause? More importantly: solution?

again, thank you!

Mike

[mjbattmer]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Plainbill, thanks for replying.

Now, an update: After letting the monitor set overnight in a cooler place, I turned it on and it now stays on for about 8 seconds then the screen flickers and slowly shuts down around the eleven second mark. I shined a bright light on the screen and I can see faint images.

Cause? More importantly: solution?

again, thank you!

Mike

Spoke too soon. Now I'm back to the 2 second black screen.

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Plainbill, thanks for replying.

Now, an update: After letting the monitor set overnight in a cooler place, I turned it on and it now stays on for about 8 seconds then the screen flickers and slowly shuts down around the eleven second mark. I shined a bright light on the screen and I can see faint images.

Cause? More importantly: solution?

again, thank you!

Mike

Read this post.

PlainBill

[mjbattmer]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Read this post.

PlainBill

Here are pictures of board front and back:

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Here are pictures of board front and back:

For future reference, please don't embed pictures in the body of the post. I neglected to direct you to the portion of the FAQ which deals with the proper way to attach them.

The picture of the top leaves a lot to be desired, but will do. The one of the bottom is quite good!

Red circle. That transistor looks like it may have overheated, but you have a better view.

Blue circles. What is the resistance between the two points? Same for yellow circles.

PlainBill

[mjbattmer]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

For future reference, please don't embed pictures in the body of the post. I neglected to direct you to the portion of the FAQ which deals with the proper way to attach them.

The picture of the top leaves a lot to be desired, but will do. The one of the bottom is quite good!

Red circle. That transistor looks like it may have overheated, but you have a better view.

Blue circles. What is the resistance between the two points? Same for yellow circles.

PlainBill

Sorry about the imbedded pics.

Looking at the transistor, it appears fine, attached is closeup pic. The one in question is on the right.

The resistance between both points is .366 (meter set on 2k).

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Sorry about the imbedded pics.

Looking at the transistor, it appears fine, attached is closeup pic. The one in question is on the right.

The resistance between both points is .366 (meter set on 2k).

As we would say - dead nuts on. Not a problem of an open or shorted transformer.

I just had a brain flash. They covered the wires with glue to prevent arcing. But some of the glues turn conductive with age. I was going to have you scrape i off so we can trace the paths. Scrape it off, try the monitor again, if the problem continues take another picture. You are going to have to make some measurements with power on.

PlainBill

[mjbattmer]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

As we would say - dead nuts on. Not a problem of an open or shorted transformer.

I just had a brain flash. They covered the wires with glue to prevent arcing. But some of the glues turn conductive with age. I was going to have you scrape i off so we can trace the paths. Scrape it off, try the monitor again, if the problem continues take another picture. You are going to have to make some measurements with power on.

PlainBill

Will do! Again, thanks.

[mjbattmer]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

As we would say - dead nuts on. Not a problem of an open or shorted transformer.

I just had a brain flash. They covered the wires with glue to prevent arcing. But some of the glues turn conductive with age. I was going to have you scrape i off so we can trace the paths. Scrape it off, try the monitor again, if the problem continues take another picture. You are going to have to make some measurements with power on.

PlainBill

Scraped the glue (pic attached) and same problem persists: 2 seconds, then off.

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Scraped the glue (pic attached) and same problem persists: 2 seconds, then off.

OK, I'm going to cover a few things here. Perhaps that will make things clearer.

1. What caps (brand and series) did you use for your replacements?

2. The two items circled in red - are they electrolytic caps? If so, what value and voltage?

3. Ditto for the two items circled in yellow.

4. The two covers outlined in green. Can they be removed?

5. A clearer picture of the top would help.

PlainBill

[mjbattmer]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

OK, I'm going to cover a few things here. Perhaps that will make things clearer.

1. What caps (brand and series) did you use for your replacements?

2. The two items circled in red - are they electrolytic caps? If so, what value and voltage?

3. Ditto for the two items circled in yellow.

4. The two covers outlined in green. Can they be removed?

5. A clearer picture of the top would help.

PlainBill

1. 6(quantity) - NTE (Lelon) VHT Series VHT470M25 - 470uf 25v 105 degree Electrlytic Capacitors and 1(quantity) - NTE (Wenten) (VHT Series) VHT220M25 - 22uf 25v 105 degree Electrolytic Capacitor.

2.Red circles: yes. Both 10uf 50v 105 degree caps.

3. Yellow Circles: yes. Both 100uf 25v 105 degree caps.

4. Removed, see attached pic.

5. Pic attached.

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

1. 6(quantity) - NTE (Lelon) VHT Series VHT470M25 - 470uf 25v 105 degree Electrlytic Capacitors and 1(quantity) - NTE (Wenten) (VHT Series) VHT220M25 - 22uf 25v 105 degree Electrolytic Capacitor.

2.Red circles: yes. Both 10uf 50v 105 degree caps.

3. Yellow Circles: yes. Both 100uf 25v 105 degree caps.

4. Removed, see attached pic.

5. Pic attached.

Thanks. This is getting me even more confused.

The output of the larger transformers are fed into the smaller transformers. It may be that senses the current, but???

OK, a few more things. Do the leads from the board go to connectors, or do they go directly to the CCFLs?

Pictures of one of the small transformers might make things clearer. Or confuse me more...

Near the small transformer in the upper right corner of the 'top' picture it says 'CE1'. Is that the full designation, or is part of it hidden?

What is the part number of the 16 pin IC on the back side of the circuit board?

I hesitate to suggest this because I am reluctant to blindly replace parts, but if you have caps handy, replacing both pairs in the inverter area couldn't hurt.

Oh, and if that fails, close ups of the lower left and lower right corners of the back of the board might help me figure out what to measure.

PlainBill

[mjbattmer]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Thanks. This is getting me even more confused.

The output of the larger transformers are fed into the smaller transformers. It may be that senses the current, but???

OK, a few more things. Do the leads from the board go to connectors, or do they go directly to the CCFLs?

Pictures of one of the small transformers might make things clearer. Or confuse me more...

Near the small transformer in the upper right corner of the 'top' picture it says 'CE1'. Is that the full designation, or is part of it hidden?

What is the part number of the 16 pin IC on the back side of the circuit board?

I hesitate to suggest this because I am reluctant to blindly replace parts, but if you have caps handy, replacing both pairs in the inverter area couldn't hurt.

Oh, and if that fails, close ups of the lower left and lower right corners of the back of the board might help me figure out what to measure.

PlainBill

CCFL's go to connectors (pics, disregard the "BL" written in sharpie, that was for my reference).

"CE1 & CE2" only verbage. (pics)

On the 16-pin IC, looks like it's Texas Instrument and reads: 55 DK 7 NK TL494C (pic)

I will replace caps this week. I do appreciate your help.

Mike

[Cronos]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Thank you very much guys, I followed your advices and my Fujitsu Siemens now works just fine... I hope it'll stay this way

I first changed 3 caps that loocked broken but the 2 seconds problem was still there... Then I changed the remaining caps and now everything seems ok.

I changed the six 470uF, the two 100uF and the 220uF ones.

Thanks again !

Cronos

[A Man]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

First time poster and amatuer electronic hobbyist here. I want to thank all the people who have posted regarding replacing the xunda caps. With this information I was able to replace the (6) 470, (1) 220, (2) 100 and (2) 10 microfarad caps and have been able to get one of my two monitors to function properly.

I completely removed the power supply and replaced the caps, then powered it up on the bench to test the +5VDC & +12VDC outputs. Before I could complete the test, I was startled by a large "POP!" and a burst of electrolyte from an incorrectly installed cap. (I should stress the relevance of safety glasses here.) Replaced it again, this time getting the polarity correct, checked the power and all was A OK. I heard a clicking sound which I understand is the "switching mode" since there was no load. I reinstalled the power supply to the video board and LCD and everything works great!

However, my second power supply is still inop. I replaced all of the same caps but it has no voltage outputs and no clicking. It has a different schematic/layout as well as a different number of 860-ABO-1700 200-000-1700A J10-005D. I started checking the fuses and I believe I inadvertenly touched my probe to the large heat sink on the input side and shorted out the fuse. However, upon replacement, it immediately pops. I have removed the input transitor (7N60B) for further testing but I am unsure where to proceed from here.

Ideas?

Regards

[Scenic]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

checked the rectifier for shorts?

[EGuevarae]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

checked the rectifier for shorts?

Agree. That would be my first guess. I've seen it more than once on 700P (the 17" version)

[A Man]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

checked the rectifier for shorts?

What and where exactly is the rectifier? And how do I proceed to check it?

[Scenic]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

the bridge rectifier is the black "box" below the "Caution" warning.