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bigmessowires

bigmessowires

68020
So about three years ago, I bought a box full of Mac Plus motherboards. Hey, everybody needs motherboards, right? Because of... the reason. And since then they've been gathering dust in the closet.

A few days ago, I bought a Mac Plus on eBay, because I couldn't resist the single blurry photo and "STEVE JOBS!!!!!!1" description for the price of $0.06. Six cents!

The Mac Plus arrived today, and right away I noticed something fishy: no motherboard. No motherboard? If I only had a... wait a minute! WAIT A MINUTE!! This is it, the moment when my past useless purchases suddenly look smart and everything is right with the world!

Plus, meet motherboard. Motherboard, meet Plus. Will they make beautiful music together?

Alas, it wasn't meant to be. Putting everything together, I got a cheery "beep!" when it powered up, and some floppy drive noise, but the screen stayed dark and the room quickly began to smell like burnt electronics.

Before I cut the power, I noticed the telltale red LED inside the floppy drive. Isn't that only present in 400K floppy drives? If so, somebody stuck a 400K in this Plus before stealing its motherboard and throwing it in the dumpster. Maybe I can salvage that, at least...

 
poor guy… heck yeah …if the 400k drive works… man that would make the whole thing worth it!

I like your story though.

I'm glad you started posting here again you disappeared for a long time.

Charles

 
have you inspected the AB yet?

does anything look rather toasty?

Charles

could have just been a lose solder joint arching.

maybe take the plastic off and look for some black carbon tracking :)

then just flux it and re-flow it.

 
I haven't yet - is that a common failure?

One thing I didn't mention could possibly explain the black screen: when I first opened it up, I noticed the red suction cup thing (cathode?) from the analog board wasn't connected to the CRT. I pushed it back into place, but it didn't seem to "snap" into place the way I expected it would. I think the metal clip inside the suction cup was a little deformed, so maybe it didn't seat properly into the depression in the CRT. Anyone ever seen that happen? I didn't want to mess with it much, since this is the exact part of those Macs where the high voltage lives. Bzzzzzt!

But honestly, this Mac is so dirty and banged up, with one corner chipped off, it literally looks like it came out of a dumpster. It probably died and was thrown in the trash after somebody pulled the motherboard.

 
blast it out with your air compressor.

inspect the suction cup again… you will see how it attaches to the tube.

Its hard to tell what is what with dust all over it.

Its common to have a loose solder joint in the AB with the 128/512/plus

 
I tried powering it on again, and whacking the left side of the case with my hand a few times. A couple whacks produced brief but recognizable flashes of the Mac desktop and disk icon. So there are some loose connections or bad solder joints for sure, if I can just determine which ones. I still don't know about the burning smell... one step at a time!

 
Refresh the solder on the two analog board connectors (the one to the yoke and the one to the logic board). That should bring the picture back, at least.

 
Refresh the solder on the two analog board connectors (the one to the yoke and the one to the logic board). That should bring the picture back, at least.
Click to expand...
What he said. When you look at the side of the analog board where the solder joints are it should be very obvious which ones are bad. Every one I've seen had obvious cracks in the solder. Easy fix.

 
OK, there's some obvious blackening on J1, which connects to the CRT. Looks like someone's been here before: there are scrape marks on the board. But before I try resoldering it, what's a good way to remove the residue from the adhesive tape? I don't want to get that stuff mixed in with the solder.

J1.jpg

It looks like the flyback transformer was also replaced in the past, and the resoldered connections don't look so great. Should I do anything with these, or just leave it?

flyback.jpg

The rest of the board looks OK visually. I don't see anything obviously blackened or deformed. I've never tried doing rework on a broken Mac before. This is fun!

 
Surgery successful! I resoldered all the pins on all three analog board connectors, and also bent the clip under the suction cup where the flyback connects to the CRT, to make sure it was making solid contact. It lives! The burning smell seems to have vanished too. I tested it outdoors, in case the whole thing burst into flames when powered on. :-)

darkcastle.jpg

One mystery, though: Floppy Emu failed to start up when connected to the external floppy port, which is something I've never seen before. I poked and wiggled and hit Reset a bunch of times, and then it started working. Maybe the 5v supply is out of spec, and causing trouble for Floppy Emu... I'll check it out.

 
yeah that could be!

maybe the 5v is funny… or the floppy port has some corrosion in it.

other then that nice work chief!

 
even if you didnt have the plus mainboards, you could have wired your plus too emulator in there along with coding the CRT drive in the firmware. Theres your plus :-)

 
you could have wired your plus too emulator in there along with coding the CRT drive in the firmware
Click to expand...
that sounds pretty hard core!

do you think someone could do this with a RAP PI?

i would assume one would need to make a custom interface board .

i have no idea why, techknight, but that sounds like an awesome idea!.

considering i have (3) se/30's now and no main boards for em :)

 
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