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mAcTX - ATX to Classic Macs

Trash80toHP_Mini

NIGHT STALKER
Very nice! Since you've said that fitting everything into and rewiring the original can's bits isn't a concern/something you'd wish to encourage, I've re-thought the IIcx installation. Designing a new can to the mounting spec of the old wouldn't be a big deal. Galvanized steel, laser cut with perforations along the bend lines would make it a simple fab using a Big Box available seaming tool. Install own topped box with a large opening for plugging in your board as intended in the bottom could work out nicely. Are strain relief blocks for AC wires readily available?

 

tokyoracer

Well-known member
80 watt picoPSU - $30 on Amazon. Grab yourself a small 12v power brick from your favorite charity shop and wire it up to the original power socket, and you have a complete stealth PSU replacement. I tested the fit out with one of the early Rev1 boards in a IIsi case and when reusing the original PSU harness there is plenty of space to spare to fit a bare 12vdc power supply inside.
Neat, I totally forgot about the Pico solution! Wouldn't be too difficult to hook it up to the standard 3-pin 'kettle' socket either if short enough. 

 
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blusnowkitty

Well-known member
Good news - rev2 boards are in today! I've built a couple of them up for testing and here's what we've found:

  1. 74LS04 inverters don't work - they'll immediately cause the power supply to turn on as soon as they get 5VSB. 74HCT04s work as expected.
  2. The support holes for the Mac 10-pin plug aren't aligned properly and cause an extremely tight fit in the PCB
  3. The resistors for the Power and Standby LEDs are too low causing near blindness when looking at.

I'll be sending off some kits to @Compgeke to see if we can get the 74LS04 issue worked out, and  then it's onto Revision 3! As far as layout goes this is more or less what the final board will look like. Last two pictures are of the board itself plugged directly into a IIsi and the board sitting in the empty IIsi PSU shell. Plenty of space!

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Compgeke

Well-known member
The good news is I think I've got the 74LS04 issue sorted out ahead of time. Using the earlier test board I hacked up a super professional test jig and managed to get the 7404 and 74F04 working. I'd imagine the 74LS04 should also work now. 

Something I might also play with is using an NPN transistor. I should be able to more or less "switch ground" so to say by powering the transistor the /PFW rail.  That's not something that'll be showing up on the final design though, more of a curiosity test. 
 

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superjer2000

Well-known member
The transistor approach is what I did  when adding soft power to my IIci and IIsi using ATX PSUs. Two resistors and a transistor on a really small board and presto - soft power. The details are in a thread I linked to earlier on. 

 

superjer2000

Well-known member
Looking back at that thread I think I had indicated I used a PNP transistor but I think it was an NPN transistor as I think the power on signal from the Mac logic board goes high when the unit is turned on. The transistor then inverts that to a low signal to turn in the ATX PSU. 

 

blusnowkitty

Well-known member
Looking back at that thread I think I had indicated I used a PNP transistor but I think it was an NPN transistor as I think the power on signal from the Mac logic board goes high when the unit is turned on. The transistor then inverts that to a low signal to turn in the ATX PSU. 
This design is pretty much final; I don't think we're going to move to a transistor unless something drastic happens with the 7404. That said, there is a "just for fun" Micro edition of the adapter board, made almost entirely with SMT parts that does use a transistor. We'll see if that turns into a shipping product when I get my hot air gun. https://twitter.com/compgeke/status/1201714914584231937

Tonight it's time for a little bit of fun! We're almost to the final revision so it's time to start writing up the paperwork. I felt it would be particularly appropriate to do it on classic Macs, so here you go. Initial vector work is done on my Mac II with dual displays (LC II is just a monitor stand right now) in Illustrator 5.5, linked to my green SE via serial because the Mac II doesn't support 1.44MB floppies, then copied over to an iMac G5 with Illustrator CS3 to print. I bet you this entire table uses at least 500 watts combined.

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Compgeke

Well-known member
I managed to get V2 boards a day early and really early. Like check tracking when I got up and "Delivered: 6:54 AM".

Electrically they work 100% fine. No need for bodge wires to make them work! 680 ohm resistors have gotten the 7404 to work properly, no matter which variant you install.  You'll notice some bodge wires here - that's playing with current handling. Using just the fairly small PCB traces, I can power a Mac IIci, Supermac Spectrum/24 PDQ, RasterOps PaintBoard Li, Toby video and a single 3.5" Quantum hard drive. The voltage starts to sag quite a bit though - getting me barely ~4.7V. That's not good enough. Add a 2nd hard drive and it'd drop below 4.6V and the system won't start.

The patch wires there are just for extra current handling. They're 20 gauge copper so not terribly big. With these I can run all the above plus a 2nd hard drive and still get 4.8V. The next board revision will have planes rather than small traces and should help significantly.

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As for the placement, the board now has the 10 pin on the opposite end of where it was before. This allows it to plug into a IIsi motherboard directly. There's plenty of clearance between it and the SCSI connector so that won't be an issue. 

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The next thing are the LEDs. Doing some testing I had with random chinese $0.01/ea LEDs, 4.7K worked great. Of course, we have higher standards for actual stuff and called for Cree LEDs (~$0.10/ea as singles, not a huge difference). I've got some of the red Crees but they're way too bright on the 4.7K resistor off the 5VSB rail. Upping it to a 10K helps, but the LED is still retina searing bright straight on. They really don't need much current. We're going to grab some Lite-On LEDs and hopefully they'll be somewhat worse LEDs. I mean that in a good way. Picture below has Chinese Green old school tech in front, Cree in back, both on 4.7K resistors on a 5V rail.

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Next board will be ordered Soon(tm). It's going to move +5V and Ground to planes, clean up the resistor placement and include standoff holes. If it works fine and can handle heavy loads, it'll become the final revision. 

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Overall, project's going good. Here's a pile of test boards I've built :)  

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blusnowkitty

Well-known member
Good news and bad news. Good news is that I got Rev 3 boards in today and they're looking great! Switching to Lite-On LEDs has also solved the problem of status lights being way too bright - I'm pretty sure those CREEs we bought last time were for things like emergency exit signs and not general purpose indicators like what we need. The bad news is that at least for me, 680 ohm resistors aren't working as they only cause my IIsi to power on for a second and then shut off. This happens on both HCT04s and LS04s. If I go back to our old Rev 1 resistor configuration (10k and 47k) I can get an HCT04 to come up but an LS04 will not come up. I'll be sending some boards to @Compgeke to test to see if he can replicate the issue. In the meantime, pictures!

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Trash80toHP_Mini

NIGHT STALKER
74LS and 74HCT family logic probably shouldn't be expected to behave in exactly the same way on identical PCBs from what I recall of Don Lancaster's Cookbooks.

https://electronics.stackexchange.com/questions/358620/74ls-vs-74hc-series-ics-for-ben-eaters-8-bit-computer

http://www.elecdude.com/2014/07/differences-in-cmos-4000-series-74ls-74hc-74hct.html

Apologies if you've already covered this in your research, just figured familial characteristics might be giving you wonky results and so should mention it.

 

blusnowkitty

Well-known member
On second thought, I'm wondering if the IIsi's soft power circuit does something a little bit weird and needs an HCT04 and different resistors. What I wouldn't give for a  scope right about now.

I'll get some prototypes sent over to @Compgeke for evaluation and after that... Does anyone else have a IIsi and would like to try a couple boards out early?

 

Compgeke

Well-known member
And as an alternative to that, anyone in the Bay Area or Sacramento Area have a IIsi I can borrow for testing? I'll even recap it for ya if it's not yet recapped as long as I can get something to test with :)  .

 

Trash80toHP_Mini

NIGHT STALKER
The bad news is that at least for me, 680 ohm resistors aren't working as they only cause my IIsi to power on for a second and then shut off. This happens on both HCT04s and LS04s. If I go back to our old Rev 1 resistor configuration (10k and 47k) I can get an HCT04 to come up but an LS04 will not come up.
If the soft power signal is one way, adding zener diode to make sure you're not getting any bounce back from the circuit couldn't might help. I see "soft power bypass" on the silk screen layer of your board, but not a dedicated bypass cap across the legs of your IC?

 
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blusnowkitty

Well-known member
If the soft power signal is one way, adding zener diode to make sure you're not getting any bounce back from the circuit couldn't might help. I see "soft power bypass" on the silk screen layer of your board, but not a dedicated bypass cap across the legs of your IC?
I've tried adding a cap and a diode across PWR_ON and /PFW on the inverter, no luck there. The soft power bypass just shorts PWR_ON to GND on the ATX supply and it's only there for Macs whose soft power has failed.

 

blusnowkitty

Well-known member
You should have a bypass cap between +5V and GND on your IC to do it by the book.
No luck there either. I'll be getting some boards over to Compgeke on Monday; he's got a lot more test equipment than I've got.

In somewhat related news, I've noticed a layout issue where 5VSB to the Mac goes through one of the 680 ohm resistors for the inverter. That drops the voltage just enough where a IIsi can't boot properly.

 

Trash80toHP_Mini

NIGHT STALKER
Bypass cap there would be a standard/best practices kind of thing. Adding that cap removes one variable from degubbing your design. Don't recall offhand which family's voltage range tolerance is much tighter, but it's significant IIRC. If nothing else it'll probably make for less problems down the road when user's Macs might be in the edge case range. 

 

maceffects

Well-known member
Sorry for my late entry into the party, but thinks look like they are shaping up well.  I must say, I think this is really a valuable project.  I am glad to see you guys tackle this.  I think projects like this are really the future of vintage computers. 

@JDW This was the first time I saw your SE/30 video, thanks for sharing that.  I'm going to give that a shot with some of my SE/30s!

 

JDW

Well-known member
@JDW This was the first time I saw your SE/30 video, thanks for sharing that.  I'm going to give that a shot with some of my SE/30s!


Great!  Feel free to comment under my video on YouTube to let me know how well it worked for you!

 

Compgeke

Well-known member
More progress tonight! I don't have the IIsi stuff or Rev 3 boards in the mail yet but I do have a transistor test setup. I can confirm everything works fine using a 2SC3904 NPN transistor and a couple resistors. It's built on a piece of solder breadboard with some machine pins soldered on so I can just plug it in the 7404 socket and pull the resistors off the PCB.  Don't mind the bodge wires here - they're just making up for the Rev 2 board still be traces, easier to rework than planes. 

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The Quadra 650 also works fine with the 74LS04 (and two 680 ohm resistors) and a 74HCT04 (with no resistors). Snowcat tried building a transistor setup for his IIsi and it's still not working - the 74HCT04 is the only one that's worked right for him. On Friday I'll have the IIsi board and I can start figuring out if it's his board or if the IIsi is weird. 

As a bonus, here's a video of the setup working. The first one I've actually recorded of it working. Sorry about the focus! 





 
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