2017 MacBook Pro 15 " - Can't connect to external monitor properly

[drawrs]

MacBook pro 2017 touchbar 15 inch on the external monitor.

I broke the LCD screen, since then I'am using second monitor as main display. Everything seems normal for a year but then I got this problem. Anyone know what is this and how to solve it? The external monitor was fine, I've tested it using another mac.

At first I thought it is because the Monterey OS, it's still beta. But the problem come after weeks later. Now I downgraded it to Big Sur but the problem is still there.

Also after the macbook entering the OS (this is where you see the login screen) the external monitor automatically sleep because there is no input detected.

I already run the apple free diagnose (Option + D on startup), but no issues detected.

Appreciate any advice, thank you!

 

[ptfuzi]

Looks like issues with cable or even graphics card.

Did you try to connect to other mac just to make sure?

Also you can do Pram and SMC reset

 

[drawrs]

Looks like issues with cable or even graphics card.

Did you try to connect to other mac just to make sure?

Also you can do Pram and SMC reset

Yes I tried it on another mac and it worked fine, I also did a Pram and SMC reset but it had no effect.

I also suspecting the graphics card, but the apple system diagnose didn't telling that problem :/

 

[ptfuzi]

Yes Aplle diagnostics might not always reveal those issues as detected problems

 

[holycowe]

Mine did same thing.
Open it, disconnect the LCD connector (middle top) and use your external as main.

 

[DeltaMac]

What connection are you using on the external monitor?

 

[holycowe]

Thunderbolt Display Through thunderbolt 2-3 adaptor. Pretty sure any monitor will do

 

[DeltaMac]

Thunderbolt Display Through thunderbolt 2-3 adaptor. Pretty sure any monitor will do

Well, yes -- with the right adapter. But most external displays are not thunderbolt, and some adapters are not necessarily reliable on every type of graphics connection.
For the OP, if the external monitor works on another Mac, you should try a different adapter on your MacBook Pro.