Macintosh Powerbook 145B - Trackball not working correctly

[TheCapfather]

I have this Powerbook that I bought some time ago and it was not working, not even turning on. I was able to fix it but there are still some things not working correctly.

When using the trackball, the mouse cursor is not moving up/down, only horizontally:


So I started by disassembling the laptop in order to access the trackball. Just taking the back cover gives us full access to it. There are a couple of screws to take out and a flex cable connected to it that I needed to disconnect in order to separate the trackball apart from the laptop.

Then 4 more screws to separate the PCB from the trackball.

I was inspecting the board to see if I could find something looking bad, and indeed I did. There are 2 emitting diodes and 2 receiving diodes for each of the positions (horizontal/vertical) and I could see how there was a bit of corrosion on the legs of some of them. I cleaned it all as well as I could and then put it together to test the trackball, but the vertical movement was still not working.

I took it apart again and I measured the diodes with the multimeter on diode mode. Here I could see the diode marked as LD4 was reading open circuit (OL) in both directions, which didn't seem right by comparing it to the reading of the diode next to it, LD3.

LD4 (bad diode)

LD3 (good diode)

So I think that is the issue most likely.
I'll try to find a replacement diode and see if it works. I'll post with the updates!

[TheCapfather]

I was able to get online a pair emitter/receiver diode similar to the one used on this board. It was not the easiest thing to find, because most of those diodes I found were like the usual LED form factor (rounded). But I needed one of those that, once soldered "vertically", would emit/receive horizontally if that makes sense .
Anyways, this is what I needed and I was able to find them on a local store so I didn't have to wait to get it from China.

I didn't really know which one, on the board, was the emitter and which one was the receiver, so I just tried soldering the replacement emitter on LD4 and the receiver on LQ4 and see if that worked.

And it did!!
I put everything together to test it and, as you can see, it works very well:


Quick and easy fix on this Powebook 145B