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There was one on one of the sweep lines but I fixed it.

That’s right.

I tried piggybacking on top of all four chips that can cause an error code with a 4 digit, and nothing changed.  I then replaced all the chips with sockets+chips, still no change, although the chime no longer sounds.  Could the fault be in the muxes or buffers?

So I replaced both F7 and G7, but the same error persists.  Should I continue replacing chips or try something else?

In my other topic I discovered that there was a dead short across the +12v and ground rails of the 400k floppy drive out of my Mac 512k.  I've traced the short from there to the cable that leads to the PCB surrounding the platter motor.   Is this something I can realistically fix or would I be...

Can you describe that method for fixing bad chips?  I know about piggybacking to add more RAM, but I've never heard about it in this context.

From the code it seems like the last digit is 4.  Wouldn't that narrow it down to F7, since all the G chips have a 0 for the last digit?

What would be the correct DRAM IC I would need?

I have not replaced the caps on the logic board yet -- when I ordered the analog board caps I forgot that there were any on the logic board at all.  I'll order them soon. In the meantime, I'd like to try to get it working.  After giving the board a good wash, I now get a good bong, but a...

Sorry for chain-posting but I have an update, and I can't seem to be able to edit my posts here.  The culprit was the floppy drive; there's apparently a short between +12v and ground somewhere in it.  If I disconnect the drive, I'm greeted with a distorted bong, and a distorted Sad Mac on the...

One more thing:  Following Dead Mac Scrolls, I tested the resistance across CR21 in-circuit and found that it seems to be a dead short.  It says to replace it in that case.  I'll do that, but after taking it out, I don't measure a short across CR21, but still measure a short across its pads. ...

I got one of those optocouplers and installed it, and also recapped the analog board.  No change.  Are there any other likely culprits?  

Sorry to necrobump this topic again, but is the Classic II flyback compatible with older models?  Or did they use a different one there?  I have a parts Classic II and want to know if I should harvest its flyback.

Do you know the appropriate replacement part number?

I'm working on a dead 512k that's making a rapid clicking noise when turned on.  I took an audio recording and uploaded it here: https://drive.google.com/file/d/12m4cIr_g4gwdeV6ooGvvR8RU5sfe1Vt7/view?usp=sharing I get no chime and no video.  Probing the 5v and 12v lines going to the logic...

Thank you, that fixed the problem!  I opened it (without even needing to desolder it from the analog board) and scraped all the metal contacts inside, and now I'm testing continuity across it. But now I'm still not getting any power from the board.  I'm seeing that I'm measuring an open circuit...

So I'm working on resurrecting a Mac 512k and I think I've stumbled across my first problem -- the power switch seems to be dead.  I measure no continuity across it in either position; I've tested for continuity between each leg and other spots on its trace.  Does anyone know of a suitable...

I'm working on a dead IIci floppy drive.  I already disassembled the floppy loading mechanism and lubricated it, and now it moves smoothly (it was totally jammed before).  Now I seem to have two problems, and they may be related.  The first is that the auto inject motor seems to be stuck.  I...

I don't know if this is normal, but I'm seeing DC offsets on all the clocks, not just the 50MHz.  Here's a shot of the output of the 50MHz oscillator:   And here's a shot of the clock input to the 68030:  https://i.imgur.com/yeeY1FF.jpg

I'm measuring a perfect 25MHz sine wave on the clock pin and a perfect 50MHz sine wave on the oscillator output.  ARST idles high and goes low when I hit the reset button. I already had to jump all three address lines to the ROMs that ran under where the battery was.   I'll check the...