Portable blank display row after recap

[Aeroform]

Hello! I just recapped a Macintosh Portable. It boots and seems to work fine, however, it has a row about 20-30 pixels high at the top of the screen that doesn’t work (see images). I’ve tried several displays, so it must be something on the mainboard that causes it.

Any tips for likely culprits / troubleshooting? I don’t have much except a multi meter to beep out traces etc. Can a wrongly installed capacitor cause this issue?

Is there a simple guide to points where I can check continuity for the caps I installed? I checked for shorts and that they were all connected to ground OK, but the positive sides were harder to check on most of the caps.

Thank you!

 

[Aeroform]

Started poking around the contrast curcuit and seem to have found a broken trace going to Q12. It’s on the other side of the board so will hunt around some more to hopefully not have to run a super long bodge wire

 

[Aeroform]

Spoke too soon. Everything in the contrast curcuit checks out OK. The hunt continues.

 

[Aeroform]

I've traced out and double checked all caps, so am fairly confident they are all in order. Also traced out a ton of other things as suggested by gemini, but still no progression in tracking down the issue. Will trace out all vram / video driver chips etc if no one has a better idea on where to look?

 

[techknight]

Make sure you didnt blob a capacitor solder joint over to an adjacent trace. its super easy to do.

It's either missing the M clock, or the panel itself is shot which sadly, is increasingly common now.

It is possible the contrast drive signal is an issue, the only way to verify that is a scope. But ive not had that issue.

 

[Aeroform]

Make sure you didnt blob a capacitor solder joint over to an adjacent trace. its super easy to do.

It's either missing the M clock, or the panel itself is shot which sadly, is increasingly common now.

It is possible the contrast drive signal is an issue, the only way to verify that is a scope. But ive not had that issue.

Thank you, I’ve checked all caps and they should be ok / not shorted to other traces. I haven’t updated this thread, but I did ultimately find a broken trace and several with high resistance on the FPData lines as the vias around J20 were eaten up. I’m still waiting for some supplies but will get those repaired and update if that did the trick. I’m still surprised 90% of the display looks good despite these poor traces.

Panel is good, I tested several displays and they all had the same horizontal line.

 

[techknight]

It is entirely possible that is the issue if the resistance is high.