jmacz Mac IIfx Project

[jmacz]

Finally found a IIfx (part of a Macintosh lot I lucked into and picked up over the weekend). Looks like it will need some work. I have not had a lot of time to look at it so far but some observations:

• Exterior looks clean and in good shape.
• Interior also looks relatively clean and the motherboard looks to be pretty good shape except:
  • There are two surface mounted caps (16V 47uF) that are leaking.
  • Few bits of corrosion but nothing very serious at least eyeballing it.
• Will not power on - no activity whatsoever when you press the power button.

Little Debugging of Power Issue

Placed two working batteries in the battery holders. Multimeter showed the batteries were good - no effect.

Placed my recently rebuilt Macintosh II power supply in - no effect.

Tested the IIfx power supply in my Macintosh II - works fine so the PSU is good.

Used a multimeter to watch the voltage on the PFW pin (motherboard to PSU) and saw 0V when pressing the power button.

Either something's wrong with the switch or something's wrong on the way to that power being delivered to the PFW pin. I have not tried providing power directly to the pin to get the power supply to turn on. Didn't have time.

Hopefully get a chance to spend some more time with this next weekend.



Some corrosion here:

 

[3lectr1cPPC]

First thing I'd do as you've caught on to is to swap out those two surface mount caps there, and probably also the axial nearby.
Here's cap reference from my site: https://macdat.net/cap_reference/apple/macii/maciifx.html

That page states this as well, but - the IIfx board was either populated with tantalum or electrolytic caps in many spaces. If you look, you'll see two sets of pads for each of these caps, one for the tantalums and one for the electrolytics. Luckily you've got the tantalum ones. Still, nearly every tantalum IIfx still has those two in the power section, although I do believe I've heard of one of them that didn't there either.
So, when recapping, you can actually use the two sets of pads above those two electrolytic caps, which are better sized for tantalum caps (if you are replacing them with tantalums that is).

As well as that, one of the tantalum caps on the IIfx is known to blow up as well due to being possibly underrated from the factory, capacitor C1. (@joshc can confirm, I believe he's the one who first documented it).
In any case you'll probably want to replace that one too.
Original value is a 47uf 16v, replacement should be a 47uf 25v. This should prevent the new one from ever blowing out, at least, not for a long time.

Good luck!

 

[jmacz]

Hmm, my C1 cap looks to be ok but I will proactively replace it. I saw that you had a count of 14 47uF 16V caps. Did some of these FX's come with that many electrolytics? Mine only has 2 electrolytics on the board so I was only planning on replacing those (+ the C1 now).

 

[3lectr1cPPC]

Yes, some unlucky IIfx boards got all those 47/16s as electrolytics.
You'll be able to tell which ones they are based off of which caps have an extra set of pads next to them.

So, if I were you I'd replace those two SMD Electrolytics, the axials, and C1.
It's possible that the corrosion on that one leg of the axial next to the lower SMD cap is from said SMD cap, but I wouldn't chance it.

 

[joshc]

You don’t need to replace the axials just yet IMO.

Just start with the two electrolytics C9 and C24 and see if that helps first. If not, it’ll be a problem in the startup circuit. References for that below.

Downtown Doug Brown » Explanation of the Macintosh II/IIx power on/off circuit

www.downtowndougbrown.com

I actually personally haven’t had the cap near the hard drive connector blow yet, across three different IIfx machines and 4 boards. Never used anything but a 47uf 16v but it probably should be uprated. I think @olePigeon has documented this before. I wouldn’t worry about it until you get the machine starting though.

 

[jmacz]

Awesome, thanks for this!

 

[olePigeon]

Numerous people have had C1 blow up, myself included. It leaves a little crater. I recommend 20v rating, but I'm no expert.

 

[3lectr1cPPC]

Ah, I misremembered who first brought up the issue, sorry joshc!

 

[jmacz]

Numerous people have had C1 blow up, myself included. It leaves a little crater. I recommend 20v rating, but I'm no expert.

I've got a 25V on the way just in case. I do not want to risk a crater for a cheap cap and a few minutes of labor

 

[jmacz]

I recapped C1, the two 47uF caps, and all the axials.



While recapping, I found the reason why the IIfx would not power up: broken traces. Two sets of them next to where the electrolytic caps were. Of course. Two next to this cap. Sorry for the bad pictures... not sure what's up with iPhone's macro lens, always looks distorted a bit.



And three next to this one.



So had to route around the breaks.



And here.. for this one, I had to make a 'stop' in between as there was a via there and I wasn't sure if something else was connected on another layer so had to hit the via first and then down to R23.



Gonna clean up the solder on the axial cap tomorrow.

But with the new caps and the bodge wires, the IIfx is booting now without an issue. Power supply is good and I will leave it for now -- will do an ATX conversion like on my Mac II if it fails.

Now I need to order yet another ZuluSCSI and probably get two meow toasts to load CR2032s for PRAM.

Machine only had 8MB of memory. Guess I will need to shop for some more. And I also need to clean the floppy drive at some point.

 

[joshc]

Woohoo! Nice work. Don't forget to buy at least a 64MB RAM set from @hyperneogeo

Checking interest for another run of IIFX 16MB ram modules

I haven't done a run for a bit and I'm checking to see if there is actually any interest in another run.

68kmla.org

 

[jmacz]

Woohoo! Nice work. Don't forget to buy at least a 64MB RAM set from @hyperneogeo

Checking interest for another run of IIFX 16MB ram modules

I haven't done a run for a bit and I'm checking to see if there is actually any interest in another run.

68kmla.org

Oh hmm. Cool!

 

[jmacz]

Ran into a problem today. Booting is working perfectly after the fixes detailed earlier. But post boot (after reaching the Finder), I was getting random crashes and lock ups. As I wrote down the pattern (when it happens), it seems it's only during disk IO. I'm using a ZuluSCSI Mini connected via the external SCSI port, no internal SCSI device.

I tried swapping memory, video cards, etc to rule them all out and none had an effect on the issue.

I then removed the ZuluSCSI Mini and connected a ZuluSCSI 1.1 via the internal SCSI connector and used the same exact disk image I was using on the external ZuluSCSI Mini. No problems. Kept trying to repro but could not, even slamming it with disk operations.

The ZuluSCSI Mini has permanently enabled termination, but not sure how this relates to the need for a special IIfx terminator.

I then tried providing auxiliary power to the ZuluSCSI Mini (via USB) and that seems to work and stabilized things. For the internal ZuluSCSI, I had used aux power as well.

EDIT: spoke too soon, still getting the issue even with aux power. Just with external devices though.

 

[jmacz]

I went to put a scope on the pins for the external SCSI connector and then could not reproduce the issue. Go figure. Since it's not resolved and magically stopped, I'm sure it will show up again so will debug it then.

 

[jmacz]

Finished putting the IIfx back together today.

I have dual CR2032 batteries installed, using two MeowToast's and a custom cover I made that holds the MeowToast better. Without the little support, the MeowToast keeps moving around so this locks it in.



Another ZuluSCSI, this time a homebrew compact one.



And then used the custom drive slot cover model I made for my Macintosh II restoration and printed a clear light pipe for it.



And the final:



Working great so far. I'm sure I'll find some issues as I use it more but currently feels stable.

 

[jmacz]

Forgot to mention, it has 68MB of memory now thanks to 64MB I bought from @hyperneogeo and they work great! Thanks!

 

[mdeverhart]

Looks great - good work!

 

[s_pupp]

Well done!

 

[macuserman]

I have dual CR2032 batteries installed, using two MeowToast's and a custom cover I made that holds the MeowToast better. Without the little support, the MeowToast keeps moving around so this locks it in.

Any chance you'd be willing to make and sell me some of these? I bought a bunch of meowtoast and mostly haven't used them due to them moving around to much. I like the ones silicon insider made much better that lay down flat, but I'd love to use up these meowtoast ones I bought as well.

 

[jmacz]

Any chance you'd be willing to make and sell me some of these? I bought a bunch of meowtoast and mostly haven't used them due to them moving around to much. I like the ones silicon insider made much better that lay down flat, but I'd love to use up these meowtoast ones I bought as well.

I can share the model when I get home tonight. Or are you saying you don’t have access to a 3D printer even if I share the model?