Removing the analog board/CRT neck board

[LaPorta]

That would make sense. The motor on the floppy drive would need a big increase in power to drive it and could cause that crash.

As for discharge, that should work. If you plan on discharging a lot of machines, you could make one that goes straight to outlet ground, which I did.

 

[Garrett]

DId you check the voltages at the floppy port? I think that leaky caps on the AB cause the reboot of the classic. The voltages are not stable and the classic resets. So you should do a recap of the AB but also a recap of the LB!

That was precisely my speculation, but unfortunately I don't have a multimeter to test any voltages on this machine. My guess is that there simply isn't enough voltage for the hard drive to spin up. When I boot into the ROM operating system and insert a floppy, the drive's current brings down the voltage and crashes the machine. Then, as the machine tries to eject the floppies on boot, it brings down the voltages again causing the machine to reset, rinse and repeat until you break the cycle by turning the machine off.

The logic board in this machine was very recently recapped. In fact, I just received the freshly-recapped board and installed it last Friday (May 29.) What's odd is that between May 29 and June 4, this machine worked flawlessly except the delay and pattern, which I and the member who recapped the board think is related to the ROM. (He tested it in another machine with a separate analog board and got the same issue... both before and after the recap. He said reseating the ROM helped the problem, but it persists. I'm thinking perhaps the ROM socket needs some DeoxIT?)

I guess the "computer Grim Reaper" visited overnight because this machine was literally working perfectly fine one day, the next day it was acting up, and now it's unusable.  > And, of course, it all had to happen just as I was beginning to have fun with the machine.

 

[bibilit]

I agree low voltages. 

As you are able to boot from time to time, probably only capacitors for now. 

For troubleshooting purposes, I use a small psu for the hard drive only, and remove the floppy, that way the load on the analog board is limited to the Logic board. 

 

[Garrett]

Should simply having the analog board bring the machine back from the dead? When I got the LB recapped, I was considering also having the AB recapped. But I decided against it because it wasn't showing any signs of failure, and I wanted to avoid/put off having to mess with the AB because of the risks of removing the neck board. (Am I being too anxious over the neck board?)

On a silver lining, recapping the AB would mean that this machine is 100% recapped... nothing to worry about. While I don't believe it is an issue on these "newer" compact Mac models, no more paper/RIFA/filter caps to worry about possibly going bang.

 

[LaPorta]

Really, the neck board is no issue. As others have stated, removal and insertion, as long as done with some care, is not an issue at all. It is made to go on and off. As far as the analog board, first, it probably is a voltage issue/digital components not getting "clean" power/correct voltage for moving ones. Second, you cannot properly diagnose it without the analog board recap and ruling out the caps as the cause. Unlike the surface mount electrolytics on the logic board, unless the large ones on the analog board are really bad, they tend to not show any leakage, and not even bulge even though bad.

 

[Garrett]

In the photos I took of the machine before reassembling it last Friday, none of the electrolytic capacitors appear to be domed or leaking. Obviously, that doesn't mean anything.

If the caps are not causing the issue, what else could be causing the issue? My electronics troubleshooting skills is near zero...

 

[LaPorta]

I just meant that until you do replace the capacitors, you can't rule them out as the cause. Replacing them all will be your first step to figuring this out.