A connundrum: Super clean original Macintosh II... keep it stock or swap in MEGA IIfx upgrade

[skeptechsguide]

It sounds like such a nice Macintosh II, I'd keep it stock - provided it works well. If it was an old dodgy one not working, I'd throw that IIfx board in without question. A good proportion of Macintosh II were upgraded to IIfx machines so you're not committing any sins.

I knoooooow... I got totally screwed by having a lucky snag You're all starting to turn me to your way of thinking...I just hope all my cap rework does the job and they both give me a chime. And no, I haven't tried powering them up. Not gonna be impatient (he grumbles to himself under his breath)

 

[Byrd]

The Official 68KMLA Law Says: you'll get both boards working well making you even more confused about which way to go

 

[LaPorta]

I wish that law worked when you have only one board that you accidentally messed up while recapping!

 

[Trash80toHP_Mini]

I see you're in the big, bad rotten apple! I would dearly love to borrow that II board for a bit. Recreating its discrete component NuBus implementation is a major ongoing project around here. May be posted in Hacks or may be in PM Skunkworks, don't recall. If you're comfortable with recap work, buzzing and documenting that subsystem would be a major contribution to the overall study of NuBus.

I'll try to remember where the project might be and who's in on it. Fabulous find you have there, totally unscrewed!

 

[Unknown_K]

Janus would go into a 950 Media Composer setup. To be honest even the Targa cards and SEIV belong in an 040 950 setup.

The original AVID MC/1 was built around a Mac IIx not fx.

 

[skeptechsguide]

Hello All,

So, I figured I'd post an update.

I ordered and received my capacitor repair kits and pulled the board and gave it a good look-over. I dusted it, cleaned it with iso and pulled all the bad SMD electrolytics via the twisting method. It was very quick and smooth and incurred no damage.

I strongly endorse this method. I desoldered the large electrolytics.

I painted DeoxIT on to the corroded areas, SIMM slots and connectors. I let it sit overnight. I cleaned the DeoxIT treated areas with green scrubbing sponge (It's the perfect hardness to clean oxidation while minimizing damage to the solder mask, but it will cause minor degradation to raised areas and painted or silkscreen markings on chips, so be careful ). I searched the board and found only two traces that were visibly severed, connecting to the power button area.

I repaired these traces with tinned wire strands. Additional to these I found several pads for the removed SMD electrolytic caps were corroded beyond usefulness and I had to use additional wire strands to build up areas to connect the new tantalum caps. Once those were in place I decided I should probably reflow solder paste for the new caps so that I wouldn't mechanically disturb the fragile ad-hoc pads. I gently applied the solder paste and used tweezers to place the new caps. I flowed the paste and was very happy with the behavior of the pads and the new SMD caps. It was surprisingly smooth.

Then I added the large axial electrolytics. I created a wire harness for the new battery harness to attach to the back of the board. I used thin solid CAT5e wire terminated at the far end with JST-SM 4 pin locking connectors. I built a small holder from some perf board and two 1/2AA holders.

This means the batteries can be held apart from the logic board and adhered with hook and loop straps in an archival way.

Finally it was the moment of truth. I have no idea how long it had been since the system had been powered on, but at some point you've got to try. I'd done a lot of work so I was skeptical that it would work... BUT IT DID!!! No chime, and I'd only installed one bank of RAM, but it WORKED! The hard drive spun up and booted in to System 7.0! Amazing!

I figured I was on borrowed time with the OEM Quantum 40MB HDD so I connected my RaSCSI and cloned the drive over to a new image. I'm glad I did, because the drive only lasted a few hours.... Luckily I'd gotten everything, so the software install can remain contemporary. The system must have come with 1MB of RAM, because it had 4x 256KB SIMMs and 4x 1MB SIMMs. I added the 256KB modules back so now I have a pretty humorous 5MB of RAM. I've ordered some Garrett's Workshop GW4194A 4MB modules that are supposed to behave on the Mac II. I'll see how they behave with the HMMU. My understanding is that it'll only see 8MB without the PMMU upgrade.

So now my system is up and running with it's original graphics card, RAM and software configuration running off an external RaSCSI. The 800K floppy is very sticky so I still have to deal with that. Not sure if there's anything I can do to refurb the HDD. That certainly seems unlikely.

Refurbishment includes:

• SMD recap to tantalums
• Axial electrolytics replaced
• Electrolyte corrosion cleaned
• Corroded traces replaced
• Servicable parts contacts cleaned and treated (SIMMs, NuBus, MOLEX, SCSI, Serial, ADB, Audio, Speaker, PSU)
• Battery harness relocated and modified

 

[joshc]

Nice work, and a good solution for the batteries.

 

[3lectr1cPPC]

Great job on the repair, I’m surprised it fired up first try with all the corrosion! I’d expect more broken traces to be found, but looks like you caught them all!
For the hard drive, it’s possible that sticky rubber bumpers are your issue. The really old Quantums all seem to do this, they’ll work for a few hours and then kick it. It might be repairable, not sure, as long as the bumpers are the issue and they aren’t under the platters like they are on some drives, you should be able to fix it.

 

[skeptechsguide]

Great job on the repair, I’m surprised it fired up first try with all the corrosion! I’d expect more broken traces to be found, but looks like you caught them all!
For the hard drive, it’s possible that sticky rubber bumpers are your issue. The really old Quantums all seem to do this, they’ll work for a few hours and then kick it. It might be repairable, not sure, as long as the bumpers are the issue and they aren’t under the platters like they are on some drives, you should be able to fix it.

Well, the audio still isn't working. One thing I didn't do was pull the socketed QFPs (like the sound chip) and check under the socket or clean the contacts... There's something afoot, but I am feeling quite satisfied overall. This is the first time I've undertaken this much rework on a single system before. It's a very reassuring start.

Does anyone here have enough experience with these Mac II boards to have an instinct on the sound failure? The three SMD capacitors in the I-17 region (bottom right if the power button is top right) are right next to the speaker (and the sound ICs if I'm not mistaken?). Should I be pulling those chips? The corrosion was particularly intense around there, though I couldn't see any faults.

 

[skeptechsguide]

On another topic, despite extensive research I'm having a hard time nailing down specifics on the RAM capabilities of the STOCK Macintosh II. I know about the 24/32bit addressing. I know about the HMMU, but beyond that things get murky. I found THIS THREAD that tries to take a whack at it, but they say that the max is 8MB without swapping the HMMU for the Motorola MC68851RC16A PMMU. They also state that 4MB modules compatible with the Macintosh II are special and uncommon. That's where the Garrett's Workshop 4MB modules designed for the Mac II come in. The question is: how will that work? 24 bit address space equals 16MB total. If I've got 4x 1MB modules in BANK A and 4x 4MB modules in BANK B do I get 20MB? Do I get 16MB and have to use extensions to get "32 bit clean" support? Is System 7 32 bit clean? Do I just have to get 4x 1MB SIMMs for BANK B too and just suck it up and settle for 8MB? Do I try to get a Motorola MC68851RC16A PMMU from AliExpress? (I checked, and my 68851 socket does have all the pin holes required), and then use my 4MB sticks? Does adding a non-stock MMU sully the rapidly dwindling mintiness of "This Old Mac II"??

HAAALLLLP

 

[3lectr1cPPC]

Can't help with RAM I'm afraid, but have you tried the headphone jack? Speakers can die more than you'd think.

 

[skeptechsguide]

My brilliant friend @Andy discovered a satisfyingly technical and ancient answer to my questions regarding PAL SIMMs, and the background, as outlined in the PDF attached!

Then of course I found THE DEFINITIVE 68kMLA thread on the subject. Just looping it in here for reference. Of course it was already here

 

[Trash80toHP_Mini]

I now feel your conundrum, I just acquired a super clean original Macintosh II, but with a different twist. I've already got a super clean Macintosh IIfx and snagged the first release II in order to reverse engineer its pre-NuChip NuBus setup. Desolder and socket the discrete component ICs for experimentation or to try to do a schematic while keeping the board stock . . .

. . . pretty sure the gang here knows my predilection.

Be that as it may, great work on the repairs and documentation of them.

 

[skeptechsguide]

I now feel your conundrum, I just acquired a super clean original Macintosh II, but with a different twist. I've already got a super clean Macintosh IIfx and snagged the first release II in order to reverse engineer its pre-NuChip NuBus setup. Desolder and socket the discrete component ICs for experimentation or to try to do a schematic while keeping the board stock . . .

. . . pretty sure the gang here knows my predilection.

Be that as it may, great work on the repairs and documentation of them.

Oh dear, that is a conundrum, and I do deeply respect your foundational instinct to "do no harm". I come from a line of archivists and librarians so it's something I deeply understand.

My thought on this is though: If the work you are doing is fed back in to the community and builds a love and understanding that keeps other minty REV. A boards up and running with modern additions and life extensions, then its sacrifice will not have been for vanity or laziness but for THE GREATER GOOD, and it's not like it's going to die. It'll end up better than new.



I for one would love to see some posts regarding this adventure you are about to embark on.

...and thanks

 

[Trash80toHP_Mini]

I for one would love to see some posts regarding this adventure you are about to embark on.

Working away at getting the research materials together already. Live long and prosper.

 

[LaPorta]

That battery solution was a great idea. Nicely done!

As far as the 5.25" HD goes, they seem to survive quite well vs the 3.5" or 2.5" variety. All the original drives in my II and IIfx work perfectly. I swapped out my IIfx's drive for a SCSI2SD, but that is just because I need more space.