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Fix0ring a Macintosh IIfx

Byrd

Well-known member
@hyperneogeo  is a great seller, perhaps contact him directly on this site to arrange a purchase; his new modules work beautifully.  IMO it's worth upgrading a Mac such as this as they're one of the best vintage Macs to own, and you can come across random Nubus cards to shove inside and make it unique :)

 

Arisotura

Active member
heheh

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Lil' update on the floppy drive, again:

I rooted through my spare parts to find a replacement for Q4, for the sake of testing. So basically I tacked on a through-hole transistor, but as long as it's the correct type and can withstand the load, it'll be good for testing purposes. Noting that the original transistors are rated for 0.7A, and the circuits they're in drive the head motor (and possibly other motors).

I connected the drive for a test run, and... poof, magic smoke.

Guess Q3 shat itself too, as after that I had a shitty 5V on the head motor controller, but the 12V was good. I replaced Q3 as well, and went for another test run. No magic smoke this time, and the drive head moved to track0 without issue.

Maybe these transistors wear out more when the drive is full of dust and crap and things move difficultly, which would explain this failure mode.

The drive is now sorta-working... I need to readjust the various alignments now, but I managed to make it mount some disks. I'm going to see after I get proper replacements for the bad transistors. The eject motor is still weak too, it's driven by Q9 so that one may be bad too.

... so basically we've been recapping vintage computers for a while now, but is 'retransistoring' a thing? :p

 

Arisotura

Active member
So what have we been up to since the last time?

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My IIfx now has a whopping 20MB of memory. I basically sacrificed the extra 1MB SIMM I had, seeing as it wasn't gonna be useful for anything anyway, and replaced the chips with compatible 4MBit chips. I had to rewire one connection, too.

I'm still open to getting a 4x16MB set and cranking this up to 80MB, but, hey, the frankenSIMM was fun to make, in a way.

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I put some more effort into the RF shield:

IMAG1764.jpg

Most of the rust has been removed, through a mix of mechanical and chemical rust removal. Now, this thing isn't gonna look factory-fresh, unless I go through the trouble of re-plating it, which, well...

I'm probably going to go with some spray paint, ideally conductive. The IIfx doesn't seem to have entirely separate digital/analog grounds like some other Mac models, but I guess the RF shield would better be connected to the ground anyway.

The floppy disk bracket thing needs some derusting too. The case itself may use a good cleanup and maybe a retrobrite... might as well do it while I have the RF shields removed, but I'd need to get some supplies for that.

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As far as the actual computer goes, I still need to fix or replace the floppy drive. I'm afraid I might have ruined the read head. We'll see once I get the new transistors, I guess. I know a place that may have oscilloscopes and shit, which might help me realign the heads properly.

The HDD, not sure how good it is. I can connect it to the computer and read what's in it without trouble, even running some mahjong game that's in it... but I can't boot from it, it gets stuck on the welcome screen. The HDD from my LC does the same thing, but that one was basically duct-taped back to life (it had a case of the melting head bumps), so I wouldn't give it much credit... I can however boot fine from my SCSI2D. I wonder if there are some SCSI termination shenanigans involved? The original HDD has terminators installed, and upon inspection of its controller board, I found out it also has the active-termination capacitors (which seem to be what the fancy IIfx terminators are about).

The Disk First Aid utility fails to do anything to that HDD, for whatever reason.

I'm also considering what I can do regarding video output.

I guess once these are sorted, I can start using this IIfx for evil projects >:)

 

hyperneogeo

Well-known member
Thanks for all the kind words everyone. @Arisoturaif you are interested in RAM I'm always here or on Ebay. I do sell them cheaper here than on Ebay as well. Basically take 15% off the Ebay listing. 

 
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Arisotura

Active member
Long time no see, thread... seems some of it has been lost?

Regardless, I decided I was gonna reorganize my apartment, and put the IIfx to use, so I installed it with the TV for a test run...

...and somehow, it died.

I've been trying to troubleshoot it, but I'm clueless so far.

First fault is that, when turned on, it turns back off immediately. Something's up with the power-on circuit...

So I tried bypassing the power-on circuit, and even using an ATX power supply instead of the original one, but then the Mac gives no sign of life. Well, it did chime a few times, but that's about it.

I might try taking it to a place where they have oscilloscopes and shit, but right now I'm out of ideas. What could possibly cause the IIfx to die all of a sudden?
 

trag

Well-known member
The HDD, not sure how good it is. I can connect it to the computer and read what's in it without trouble, even running some mahjong game that's in it... but I can't boot from it, it gets stuck on the welcome screen. The HDD from my LC does the same thing, but that one was basically duct-taped back to life (it had a case of the melting head bumps), so I wouldn't give it much credit... I can however boot fine from my SCSI2D. I wonder if there are some SCSI termination shenanigans involved? The original HDD has terminators installed, and upon inspection of its controller board, I found out it also has the active-termination capacitors (which seem to be what the fancy IIfx terminators are about).

Could be corroded connectors. We're starting to see systems that don't work without being treated with contact cleaner, now.
 

Arisotura

Active member
Well, for the first part, turns out UI18 went bad. After replacement, the start-up circuit is behaving normally.

However, I'm still not getting any sign of life... blarg.
 

crmccluskey

New member
Thanks :p

Regardless, here's where we are this morning:

View attachment 31610

The through-holes are installed. Except for the RAM socket, I will do that one after I have received and installed the F573 -- it would hinder my already limited ability to solder that SMD chip in place.

As usual, all connections have been tested, and all the traces that run under the battery holders were verified, they are fine. BT2 is looking lopsided because it's sitting on one of the bodges.

Speaking of, a close-up of the creative bodging:

View attachment 31611

I still have to clean up that board, heh.

View attachment 31612

The original reset/intr buttons. The right one is actually still good, but the left one is toast -- it won't even press at all, plus one of the legs broke off during removal.

I replaced both for the sake of consistency mostly. I wonder if there is any functional reason why the original ones have these holes in the button part.

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I can't test this fully yet (missing one of the F573 latches that sit between the data bus and the RAM means we would only get a sad-mac at best), but I did a lil' test with batteries installed: pressing the power switch sends ~5.7V on pin 15 of the power connector, so atleast that part of the computer is working :p
Hey there. Did you happen to find old stock or a new alternative to the interrupt/reset switches? I have a Q950 I need some physical switches for, and haven't found a good replacement as old stock are low, and new stocks don't quite fit.
 

Arisotura

Active member
I just used these, they fit well. The original buttons aren't anything fancy, they're similar push buttons but mounted at a 90° angle, and they rest against a plastic holder that can be separated.
 

Arisotura

Active member
Status update on this:

I suspected the fault with my IIfx could be either the CPU, the FPU or the ROM.

I got a SOIC32 adapter so I could test the ROM chips on the ROM SIMM. Turns out one of these is bad. I'm going to see if I can get a replacement.
 

joshc

Well-known member
I got a SOIC32 adapter so I could test the ROM chips on the ROM SIMM. Turns out one of these is bad. I'm going to see if I can get a replacement.
The ROM is shared with these models: SE/30, all II-series Macs with a 64-pin SIMM socket (should include the IIx, IIcx, IIci, IIfx, and IIsi). So if you find a ROM advertised as being pulled from those machines, it should work. Otherwise, you can order a Rom-inator II or GGLabs SIMM which will also work.
 
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