2017 iMac Display -Please Help!

[Gold240sx]

I’ve got a difficult one... (I joined the forum simply to ask this question so I’m hoping you all can help me!)

I have a 2017 5k iMac 580 8gb 3.8 i5 with 2Tb Fusion Drive that I upgraded.

I put in a 4Tb Samsung 870 SSD, a 2Tb Samsung nvme and a 4.2ghz i7

After installation, everything worked as expected except I inserted the card a bit too far and seemed to have damaged the LCD a little bit as there were vertical lines across a portion of the screen that wasn’t working. I purchased a new display and used the iMac for 2 weeks Until it arrived, using the previous display without any issue.


\/\/\/\/\/\/\/\/ And This is where the problems happened. (Instantly) \/\/\/\/\/\/\/\/


1. My (brand new) display came in. (Nothing with hardware has been touched)

2. I unplugged the 2 display cables while the iMac was on. (I know this was stupid.)

3. I look at the back of the new display and noticed it didn’t have the LVDS cable. I removed the LVDS cable. (At this point I hear the iMac’s fans ramping up to 100% which up to this point had not happened before. (neither Display is connected yet)

4. I attach the LVDS cable to the new display and plug the new display in. It doesn’t turn on. (Fans still at 100%)

5. I turn off the computer, unplug it. Turn it back on, reset the PRAM, still doesn’t work. Remove the screen and test out the old display to determine if the new replacement LCD is non-functional.
Old LCD all of a sudden is not displaying an image either. Fans still at 100%.
The diagnostic LEDs on the motherboard shows 3 LED’s strong at 100% brightness. The 4th LED i am 100% sure is on but I’m also 100% sure it’s about half the brightness as the other LEDs.

I researched to see what the issue could be.
I plugged in an external monitor and the external monitor worked without an issue.
I found out that the display had a temperature sensor and assumed the LVDS wasn’t transmitting the video signal and therefore must also not of been transmitting the temp sensor signal, and figured that I must have broken the LVDS cable Which is why the fans were at 100% (default for not getting an LCD signal) and also why there was no video, so I purchased a new LVDS cable.

7. After installing a NEW LVDS cable the image didn’t display on either LCD with either cable. I very carefully transferred the LCD temp sensor to the new Display and that still didn’t seem to subdue the fan speed.

8. I’m completely at a loss at what could be the issue. I’m a little hesitant to mess with something that I knew worked and haven’t touched other than remove the display.
to summarize:

The fans are on At 100%
2 displays are not producing video. (One that worked but was damaged, and the other brand new.)
Diagnostic Motherboard LED #4 is dim But definitely on. Other 3 are bright.
External (secondary monitor is working).
2 LVDS cables are not transmitting video signal to the main display. (That or power or something) idk...
The Start Chime is working fine.

Any suggestions on what to look for, how to fix or anything else to consider? Thanks!

 

[glenthompson]

My best guess is that you fried something by plugging and unplugging cables while power was on. Could be both displays since you did it with both. Fan speed definitely caused by missing temperature sensor. No idea on the diagnostic LEDs. Since it works with an external monitor it sounds like the logic board is ok. You may have to spring for another display and cables. If you do, put the power cord in another room.

 

[Gold240sx]

My best guess is that you fried something by plugging and unplugging cables while power was on. Could be both displays since you did it with both. Fan speed definitely caused by missing temperature sensor. No idea on the diagnostic LEDs. Since it works with an external monitor it sounds like the logic board is ok. You may have to spring for another display and cables. If you do, put the power cord in another room.

The only display I unplugged while the power was on the original one. Maybe I misunderstood you though?

 

[glenthompson]

The only display I unplugged while the power was on the original one. Maybe I misunderstood you though?

Your chronology seemed to indicate that unplugging the old display and plugging in the new display both occurred with power on. No mention of power being off between steps 2 & 4.

 

[Nguyen Duc Hieu]

Too many factors to consider here:
- LCD backlight board (no light => no image)
- LVDS connector (the one on the logicboard)
- LVDS control chip on the logic board, or some small components on the logic board near the LVDS connector (if any)
You can take both LCD panels to test on another machine or test board, then you can isolate the issue (LCD panel, LVDS cable or logic board).

 

[Gold240sx]

Too many factors to consider here:
- LCD backlight board (no light => no image)
- LVDS connector (the one on the logicboard)
- LVDS control chip on the logic board, or some small components on the logic board near the LVDS connector (if any)
You can take both LCD panels to test on another machine or test board, then you can isolate the issue (LCD panel, LVDS cable or logic board).

Ok, Thank you for a response, I guess ill have to take it to an apple repair shot or something since I don't have access to another iMac unfortunately.

I did shine a very bright light on the screen to see if i could see any image being displayed without a backlight and wasn't able to see anything...

Are any of the small components on the logic board able to be fixed or are they pretty much all compnents that might need micro-soldiering to fix? On another post (and an older iMac) someone reccomended that he check his LCD inverter and since this one doesn't have a display inverter, I figured it must be a part of the main logic board.

Is there anyway of knowing what ISN'T wrong with it based upon diagnostic LED's or the fact that it's displaying a second screen image? Or what is UNLIKELY to not be wrong with it?


-----------------------------
Oh and Glen, no worries, and I apologize that I didn't mention the fact that I shut down the system and unplugged the power from the wall before plugging in the new LCD.

 

[MacRoysan]

Hi Gold240sx!

The problem is most likely that you burned the fuse to the screen on the motherboard. See attached picture where it is located with an arrow, it is very small, and has the designation F4400 and is close to the display connector.
Regards
MacRoysan

 

[Proysec93]

Hi Gold240sx!

The problem is most likely that you burned the fuse to the screen on the motherboard. See attached picture where it is located with an arrow, it is very small, and has the designation F4400 and is close to the display connector.
Regards
MacRoysan

Excuse me but I can´t see the attached picture, could you resentido. Thank you