A while back, I picked up a loose Macintosh II motherboard for the sole reason that it contained the rare (not valuable, but rare) recalled Macintosh II ROMs. These ROMs contain a bug that prevents NuBus cards from accessing more than 1 MB of NuBus space.
However, the board itself was trash due to leaking batteries.
Fumes from a battery also tend to result in corrosion throughout a board. This revision of the board does not have many electrolytic capacitors, but the image below sure seems to look like damage from that. Perhaps this board was in a stack of boards that were all impacting each other.
Further evidence for this board being in a pile, it has been physically abused to the point that four of the SIMMs slots had their tabs broken off.
This is not the type of board I would normally repair. It has so much damage that it is just not trustworthy. There is nothing more frustrating that bringing a 'fixed' computer out of storage (just to try something or play a game), only to find it isn't working again.
I scraped off the battery discharge with a plastic spudger. Surprisingly, unlike SE/30s, the battery leak hadn't cratered the PCB. If I found the board was missing layers at this point, I would have stopped. A lot of IPA along with an ultrasonic cleaning further improved the situation.
RP12 was definitely damaged. I decided to remove most of the nearby chips to assess traces and make sure they were soldered properly. I have hope at this point. (It turns out that all the other chips are working.)
Because so many traces are exposed, I decided to create my own homemade removable battery carrier. This allows me to inspect and repair traces during the diagnostic phase, without desoldering and resoldering the batteries. I snipped off some machined standoff headers.
And then used perfboard to create a friction-fit carrier that lifts off.
Because the SIMM sockets had snapped due to board stacking rather than SIMM removal, the breaks happened at the base, not at the triangular tips. This made for a relatively easy and really successful repair with clear epoxy.
The board went through many cleaning phases. The 40 MHz oscillator did not survive. I socketed a replacement.
The ROM sockets cleaned up okay, but I will always doubt them because of their starting condition (see below). In the future, I could desolder them and put in new parts. I replaced the rare ROMs with newer revisions.
After all this, the Macintosh II powers up and passes all tests! Simply wow.
This was a fun exercise. I honestly didn't think it would work. That being said, the motherboard will not be installed in a case, because I have cleaner boards that I can rely on.
- David
However, the board itself was trash due to leaking batteries.
Fumes from a battery also tend to result in corrosion throughout a board. This revision of the board does not have many electrolytic capacitors, but the image below sure seems to look like damage from that. Perhaps this board was in a stack of boards that were all impacting each other.
Further evidence for this board being in a pile, it has been physically abused to the point that four of the SIMMs slots had their tabs broken off.
This is not the type of board I would normally repair. It has so much damage that it is just not trustworthy. There is nothing more frustrating that bringing a 'fixed' computer out of storage (just to try something or play a game), only to find it isn't working again.
I scraped off the battery discharge with a plastic spudger. Surprisingly, unlike SE/30s, the battery leak hadn't cratered the PCB. If I found the board was missing layers at this point, I would have stopped. A lot of IPA along with an ultrasonic cleaning further improved the situation.
RP12 was definitely damaged. I decided to remove most of the nearby chips to assess traces and make sure they were soldered properly. I have hope at this point. (It turns out that all the other chips are working.)
Because so many traces are exposed, I decided to create my own homemade removable battery carrier. This allows me to inspect and repair traces during the diagnostic phase, without desoldering and resoldering the batteries. I snipped off some machined standoff headers.
And then used perfboard to create a friction-fit carrier that lifts off.
Because the SIMM sockets had snapped due to board stacking rather than SIMM removal, the breaks happened at the base, not at the triangular tips. This made for a relatively easy and really successful repair with clear epoxy.
The board went through many cleaning phases. The 40 MHz oscillator did not survive. I socketed a replacement.
The ROM sockets cleaned up okay, but I will always doubt them because of their starting condition (see below). In the future, I could desolder them and put in new parts. I replaced the rare ROMs with newer revisions.
After all this, the Macintosh II powers up and passes all tests! Simply wow.
This was a fun exercise. I honestly didn't think it would work. That being said, the motherboard will not be installed in a case, because I have cleaner boards that I can rely on.
- David
