Recapped Macintosh II will not boot

[davidg5678]

I am in the process of restoring a Macintosh II and have already thoroughly cleaned the case and components. After cleaning the motherboard with a toothbrush and isopropyl alcohol bath, I recapped the motherboard with tantalum capacitors. I did not see a small yellow electrolytic capacitor when ordering parts, so this one remains stock for now. I removed both of the batteries and replaced them with 1/2 AA Battery holders. These both have fresh batteries in them.

After completing the recap, I reassembled the machine and plugged it into an Apple Color HighRes RGB Monitor I know works with my Macintosh iisi. On pressing the power button on my keyboard, nothing happened on the computer at all. The button at the back also did nothing. I read online about jump-starting the computer with an alligator clip and battery -I tried this and was able to get the power supply to light up and the hard drive to spin. The display also received power but did not display any picture. I disconnected the hard drive and tried this again, but did not even receive a blinking floppy on the screen —it remained black. Something interesting is that when the computer is jump-started, the power button at back shuts it off.

Attached are some pictures of the recapped motherboard. (This was my first time using a hot air station instead of a soldering iron.) I did not really see much damage to the traces apart from one spot, but this did not look too bad. 

Please let me know if you have any ideas about how to proceed.

Thank you!

 

[AwkwardPotato]

When repairing my IIx (which has an almost identical power-on circuit) I found two issues that caused the same power-on problems that you're describing on my machine:

1. Corroded traces around UB1 and UB2
   
2. Corroded traces between the batteries and D5 and D6 (D4 and D5 on your board, I believe)
   

Might try checking for those issues on your board, although I doubt they'd fix the display problems, especially if the board isn't chiming.

 

[techknight]

Its no surprise it doesnt work. it has quite a bit of trace rot in key areas. 

Its not chiming or booting because it cannot read ROM. The likely reason it cannot read ROM is the trace rot nearby one of the ROM ICs by the batts. Theres a bunch of it there. 

 

[LaPorta]

In your first picture, there is a trace that is entirely gone above C7. As the others said, there are others as well. I am in the process of doing the exact same thing as you with my Macintosh II. There are several traces that are gone. I am looking for schematics to make it easier, but I don't think that is happening. I am going to follow them instead and just run thin wire instead of the traces.

 

[davidg5678]

Thanks for the help! I will take a better look at the motherboard and try to fix some of the traces. With any luck, my Macintosh II will start working.

 

[davidg5678]

I repaired the broken trace above C7, the trace near the power button, and the trace near D4. I also replaced the 10uf 16v capacitor with a new tantalum one. It looks like there were already surface mount pads in place underneath the axial capacitor, so I connected to these. While working on the traces, I scratched off a little solder mask on each side of the corrosion, placed solder on the exposed copper, and put a thin wire over the gap.  The system immediately powered on when I pressed the button on the keyboard -much better than before.

Besides turning on the power supply when the button on the keyboard is pressed, the computer seems unchanged. There is still no boot chime, and the screen does not display any picture or do anything besides turn on. The hard drive stops accessing after about ten seconds into startup. This is about the same as when it was jump-started. Are there much more than three damaged traces to fix?

Thanks again!

 

[AwkwardPotato]

It's difficult to tell from the angle of the pictures, but is ROM4 correctly seated in its socket?

 

[LaPorta]

I’ll let you know how mine goes. How did you go about repairing your traces?

 

[davidg5678]

After taking a closer look at ROM4, I noticed that only half the pins were inserted in the socket. I had removed all of the socketed chips when I cleaned the logic board with isopropyl alcohol, and I must have not put the chip back in correctly. After removing it and placing it in the socket the correct way, the computer was able to turn on. The hard drive seems to be long gone, but I was able to boot from a floppy disk successfully. Now to configure the computer...  :ii:  My method for repairing traces involved scraping the solder mask off from either side of the corrosion, using flux to place a bead of solder on the exposed copper of the trace, and running a very small piece of wire over the gap. (I used tweezers to scrape the solder mask and hold the wire in place.) I may go back and place a blob of hot glue over everything to keep it in place.

Thanks to everyone for their help!!! I will keep this thread updated if I encounter any more issues. I am unsure whether or not repairing the traces and recapping were even necessary at this point, but they certainly did not hurt the computer.

 

[davidg5678]

Unfortunately, things were not as easy to repair as I thought. After a few days, the computer does not want to turn on with soft power at all. After I jump-start it, I am able to get the machine to boot from a floppy disk with Norton Disk Repair Software on it (the only bootable 800k floppy I have right now.) I was entirely unable to get the machine to boot from my SCSI2SD with System 7.5.5. It works perfectly in my iisi and SE/30. The stock Hard Drive does not seem to work in this machine, and neither does a Zip Drive or the iisi drive. I suspect something SCSI related may be broken. I sprayed contact cleaner over all of the sockets and reseated the chips, but this did not help. I am unable to see any damaged traces on the board apart from the ones which I have repaired.

If you have any ideas what might be wrong, please let me know. Thank you!