21.5 in iMac display worked, now not working after re-installing screen after HD replacement

[dictoresno]

So I finished replacing my internal drives and hooked the display back up and used it for 24 hours just taped to make sure all was working well before using the adhesive strips. I powered it down, applied the strips and plugged everything back together and sealed it....startup chime and black screen. tore it all apart again and checked connections. found the display data cable unplugged from the display, not the logic board. I hooked it back up and powered it on without sealing it up again, worked fine. tugged on the adhesives and sealed it. tried to turn it on again, no dice....black screen.

I'm currently connected to the computer using screen sharing from my MacBook Air, it's up and running and fully detected by the computers system settings. I'm gonna guess there's still something wrong maybe with the power cable, but those are secure.

any other ideas? I've re-seated the connections about a dozen times to ensure they are tight.

 

[azentropy]

Those cables/pins/connectors are extremely sensitive and fragile. I also had a 2015 that I upgraded/swapped out the drive for many times. The last time though when I decided to sell it I put at 512GB SSD back in instead of the 1TB SDD I had for a couple of years I ran into the same issue. It didn't work, then it did after adjusting it, then it stopped again. I couldn't get it back after that and even tried a new cable. In fact ended up getting frustrated and wasn't careful and forgot to properly support the display when taking it off and it fell down those couple of inches and cracked the display.

A question though, when mine wasn't working it did work with an external display but since it wasn't sensing the internal display it was throttled and the fans would be start going full blast. Its that happening to you or is it fine other than the display being black?

 

[dictoresno]

the computer is perfectly fine. its running normal and when I connect via screen sharing, the internal display is recognized in the system report properly. fans are normal. like I said. I had the screen working all day today and it worked just fine before I pulled the adhesive tabs to seal it. I tried wiggling the cables and connectors to try to see if something was loose, no dice. I was gonna try to use a multimeter to check for power at the display power cable terminal from the logic board but can't find any info on which pins to check and how much voltage.

 

[dictoresno]

I have continuity on all of these circuits and everything around them, especially when compared to my old working board.

 

[DeltaMac]

Sounds like your screen is working, just no backlight (?) (You should then be able to see menus and icons by shining a light into the screen)

 

[dictoresno]

Well now I’m suspicious. I swapped my old logic board in to rule out it being the board display connectors. Now it won’t power up at all. When I took it apart the other night, I noticed the power board had tons of grey residue all over it. I wonder if the power board finally failed. I think this is the perfect opportunity to grab a nice used 2014 Mac mini and a nice display and call it a day. Maybe I’ll grab another power board also. But I’m getting tired of taking this apart and I’m currently using a 2014 Mac mini as a headless file server and love it. Can anyone tell if the PCB looks “burned”. Ill take it the rest of the way out tomorrow and check for blown caps.

 

[dictoresno]

So I ordered a new power supply, since that one looks questionable. However all caps looked fine, none blown or bulged.

I plugged the supply back in and plugged it in. With the screen off, I was able to see the first green light on showing the power supply was working. I tapped the power button and the second and third diagnostic lights lit up indicating the computer is on and the GPU working. The fourth light wasn’t lit, since the LCD panel wasn’t connected. Assuming the computer was POSTing, I connected the two display cables and rebooted. The fourth light refused to come on even with the display connected and on top of that, there is NO start up chime.

I’m going to put the other logic back in (both were working just fine) so I’m really starting to wonder about the display cables. The one that connects to the logic board with twin ended ribbon connectors (the display data cable) is the only one I can replace. The other one, the power supply, is hard wired to the LCD housing. Worth a shot replacing that cable? It seems like it may be a little loose in the top connector on the back of the display.

 

[dictoresno]

ok another update. I plugged in my other logic board and reset the PRAM while the screen was off. after verifying the PRAM reset worked and the computer rebooted fine, I hooked the screen back up and rebooted. heard a chime, but still only got 3 out of 4 diagnostic lights and I let it boot into Ventura. I was able to connect to it via screen sharing and it appears the system report is reporting the screen is detected and working fine. now that I can get into the OS, are there any other display or video diagnostics I can do to verify what's going on here? Im completely stumped.

new eDP/LVDS cable is on the way in case its messed up and also a new power supply since the other one looked dirty/burned.

 

[MultiFinder17]

I think this is the perfect opportunity to grab a nice used 2014 Mac mini and a nice display and call it a day. Maybe I’ll grab another power board also. But I’m getting tired of taking this apart and I’m currently using a 2014 Mac mini as a headless file server and love it.

ok another update. I plugged in my other logic board and reset the PRAM while the screen was off. after verifying the PRAM reset worked and the computer rebooted fine, I hooked the screen back up and rebooted. heard a chime, but still only got 3 out of 4 diagnostic lights and I let it boot into Ventura. I was able to connect to it via screen sharing and it appears the system report is reporting the screen is detected and working fine. now that I can get into the OS, are there any other display or video diagnostics I can do to verify what's going on here? Im completely stumped.

new eDP/LVDS cable is on the way in case its messed up and also a new power supply since the other one looked dirty/burned.

Given that you were considering getting a 2014 mini for a new desktop, and you already have one running as a headless server, why not just swap them? Use the iMac with a bum display as your new headless server and use the mini you have as a server as your new desktop? That way you don't need to buy any new computers and can continue using the ones you have in new configurations.

 

[dictoresno]

Given that you were considering getting a 2014 mini for a new desktop, and you already have one running as a headless server, why not just swap them? Use the iMac with a bum display as your new headless server and use the mini you have as a server as your new desktop? That way you don't need to buy any new computers and can continue using the ones you have in new configurations.

Because I love overcomplicating things. Honestly, there isn’t any room in my server rack for an iMac. Plus, I know it’s still in perfect working order aside from, what I assume, is the display connector.

The new ribbon cable and power board arrived. I’ve been able to get it to boot, but given that the old power board looks grimey I’m gonna replace it and the ribbon cable. If it still doesn’t work, I think I’ve narrowed it to the 30 pin connector on the back of the display. I ordered some from AliExpress and will whip out my soldering station when they arrive if the cable alone doesn’t fix it.

 

[dictoresno]

Ok so I replaced the ribbon cable and tested it. Works fine and booted right up. I checked the bad cable over and over under magnification and can’t see where a pin may be bad. But it was the 30 pin side that connects to the LCD side. I indeed must’ve damaged it when the screen slipped on my and yanked the connector, even though it did work after that happening briefly. All fixed. Waiting on a new set of adhesive strips to seal it up.

 

[MultiFinder17]

Because I love overcomplicating things. Honestly, there isn’t any room in my server rack for an iMac. Plus, I know it’s still in perfect working order aside from, what I assume, is the display connector.

The new ribbon cable and power board arrived. I’ve been able to get it to boot, but given that the old power board looks grimey I’m gonna replace it and the ribbon cable. If it still doesn’t work, I think I’ve narrowed it to the 30 pin connector on the back of the display. I ordered some from AliExpress and will whip out my soldering station when they arrive if the cable alone doesn’t fix it.

Hahaha, that’s legit mate. So much of the time the more complex solution is so much more fun to do than the simpler ones. I’m glad you got it working again! May she serve many more years with you

 

[dictoresno]

Hahaha, that’s legit mate. So much of the time the more complex solution is so much more fun to do than the simpler ones. I’m glad you got it working again! May she serve many more years with you

I got the macmini in yesterday and it’s working nice. Got my adhesive strips for the iMac in so I’m gonna seal it up today. The macmini came with an OEM apple 256GB NVMe SSD so I threw that in the iMac and I’ll keep it around as a backup.