PSU hack for IIci and other soft switch Macs

[Kay K.M.Mods]

I made this PSU hack a while ago. Other guys are doing the way to control soft switches with transistors. I made this in a way that doesn't require a + 5V pullup. Specifically, a photocoupler is used. This method is also compatible with G2-PowerMac. Please try it in case of PSU failure. I'll share the wiring diagram and the schematic, but if you want to know the details, please see my blog.

『Macintosh IIci PSU hack and restore』

The other day... I sent a Japanese NES(Famicom) to my friend Eric Fraxinous wh…

ameblo.jp

 

[Drake]

This would have been really handy a couple months ago, then I wouldn't be using aircraft toggles like I'm launching a 68k nuke

 

[Kay K.M.Mods]

This would have been really handy a couple months ago, then I wouldn't be using aircraft toggles like I'm launching a 68k nuke
View attachment 228

Wow it's very funny, I think this is fine, however, it's not too late to install a photocoupler from now on!

BTW, the monitor behind is 13 ”and has a tilt stand?

 

[Drake]

Wow it's very funny, I think this is fine, however, it's not too late to install a photocoupler from now on!

BTW, the monitor behind is 13 ”and has a tilt stand?

It is a generic tilt/swivel base, unbranded. Just handy to have for most monitors like Commodore, Apple etc OR sometimes compact Mac

 

[Kay K.M.Mods]

It is a generic tilt/swivel base, unbranded. Just handy to have for most monitors like Commodore, Apple etc OR sometimes compact Mac

Looks really nice, thx for share.

 

[retr01]

@Kay K.M.Mods, nice PSU in your IIci!

I use a GE PSU in my IIci. It has a Noctua fan. I am considering having the GE PSU recapped. Now that I noticed you swapped the top part with the LEDs and modified the wiring.

Does that make the PSU only to draw power as needed and control the fan?

Where can be LEDs be obtained? Do the top part need to be cut or is there a top part ready to go for those LEDs?

 

[Kay K.M.Mods]

@Kay K.M.Mods, nice PSU in your IIci!

I use a GE PSU in my IIci. It has a Noctua fan. I am considering having the GE PSU recapped. Now that I noticed you swapped the top part with the LEDs and modified the wiring.

Does that make the PSU only to draw power as needed and control the fan?

Where can be LEDs be obtained? Do the top part need to be cut or is there a top part ready to go for those LEDs?

I think the LED you're talking about is a voltmeter, but it's only connected to each volt and ground. What you have to be careful about is the negative voltage part. In this case, install the voltmeter in reverse. Good hack!

 

[joshc]

This is really the way to go with dead/dying IIci PSUs. I don't think it is worth recapping old power supplies like this anymore. There is nothing special about the original IIci power supply. The original Astec/Delta units are way beyond the end of their designed lifetime now. The other benefit of an ATX-based PSU is that it will run cooler and more efficiently than the original PSU, and has all the modern safety features that 80 plus rated PSUs have.

The IIci PSU pinout was also used for the following models: Quadra 700, Macintosh IIcx, Macintosh IIvx, Macintosh IIvi, Power Macintosh 7100, Quadra/Centris 650, aaand I think the Quadra 800 but the 800 has a different formfactor case for the PSU housing.

Here's my attempt at a 'stealth' IIci PSU, which uses a 250W Seasonic SFX unit inside the original housing. I even moved the Seasonic sticker across to replace the Astec one, so it looks like it's always been this way.

The Seasonic PSU has a built-in thermometer sensor so the fan speed is controlled from that.

Since replacing my PSU, I've had no issues with soft power - it acts really fast when the ADB keyboard power key is pressed, just as it should.

The soft power circuit I used:

My original PSU:

The Seasonic had its own filtering on the back of the AC socket, so I moved this across to the Astec housing.

The original Astec sockets were removed:

I installed new stand-offs into the bottom of the Astec housing. Went through two drill bits doing that, oops. But this meant I could dispose of the Seasonic PSU housing and just keep the Seasonic PCB and move that into the Astec housing.

Here it is all wired up to the original motherboard connector:

And all done, you can't tell anything was ever changed.

 

[Kai Robinson]

I bought the exact same PSU as this to do to the spare IIci PSU you gave me the last time i was down your way - just haven't got round to it yet. Did you use standard PC Motherboard brass standoffs to affix the seasonic PCB to the case?

 

[joshc]

I bought the exact same PSU as this to do to the spare IIci PSU you gave me the last time i was down your way - just haven't got round to it yet. Did you use standard PC Motherboard brass standoffs to affix the seasonic PCB to the case?

Yup. The drilling was the hard part, I used a decent Bosch drill but I guess I was using the wrong drill bit as it was really hard to get it through the metal case.

 

[retr01]

@joshc, this is a fantastic mod for the IIci/Q700/etc. PSU!

I am wondering, what about the General Electric PSUs? I have two IIci PSUs, the Astec (not using) and the GE.

 

[joshc]

this is a fantastic mod

Thanks

I am wondering, what about the General Electric PSUs? I have two IIci PSUs, the Astec (not using) and the GE.

What about them? They are of the same/similar age to the Astec, Delta, and LITEON. Old PSUs are old. I personally don't think any of them are worth recapping at this point. Others may disagree with that viewpoint, but you should get more longevity from a new ATX-based PSU.

 

[retr01]

you should get more longevity from a new ATX-based PSU.

I agree. Thank you for sharing!

Cheers!

 

[retr01]

One thought I have. I wonder if this particular PSU model, the SEASONIC SS-250SFD, is designed for International electrical versus another model for the United States?

 

[Kay K.M.Mods]

This is really the way to go with dead/dying IIci PSUs. I don't think it is worth recapping old power supplies like this anymore. There is nothing special about the original IIci power supply. The original Astec/Delta units are way beyond the end of their designed lifetime now. The other benefit of an ATX-based PSU is that it will run cooler and more efficiently than the original PSU, and has all the modern safety features that 80 plus rated PSUs have.

The IIci PSU pinout was also used for the following models: Quadra 700, Macintosh IIcx, Macintosh IIvx, Macintosh IIvi, Power Macintosh 7100, Quadra/Centris 650, aaand I think the Quadra 800 but the 800 has a different formfactor case for the PSU housing.

Here's my attempt at a 'stealth' IIci PSU, which uses a 250W Seasonic SFX unit inside the original housing. I even moved the Seasonic sticker across to replace the Astec one, so it looks like it's always been this way.

The Seasonic PSU has a built-in thermometer sensor so the fan speed is controlled from that.

Since replacing my PSU, I've had no issues with soft power - it acts really fast when the ADB keyboard power key is pressed, just as it should.

The soft power circuit I used:

View attachment 6436

My original PSU:

View attachment 6437

The Seasonic had its own filtering on the back of the AC socket, so I moved this across to the Astec housing.

View attachment 6438

The original Astec sockets were removed:

View attachment 6439

I installed new stand-offs into the bottom of the Astec housing. Went through two drill bits doing that, oops. But this meant I could dispose of the Seasonic PSU housing and just keep the Seasonic PCB and move that into the Astec housing.

Here it is all wired up to the original motherboard connector:

View attachment 6441

And all done, you can't tell anything was ever changed.

View attachment 6440

I noticed that the small circuit of the transistor is exactly the same as the Beezul-bulb we made earlier. I made it to control a Bi-color LED for Blue SCSI.
I have just finished the 9600 test, so I will use it to test. Since it's a Power Mac lol, I will set up another post.

 

[joethezombie]

I'll put a small warning on this topic for a heavily populated IIcx/i/700. The case has vents on top and front of the Nubus slots. Cool air is drawn in over the cards and the hot air is pushed out through the power supply. If using an ATX with variable fan, airflow through the case may not be enough to cool the area around the cards or the processor since the system load or thermister in the ATX supply may not drive the fan fast enough. My Quadra 700 was locking up randomly until I shorted the fan to run at a constant higher speed, thus providing steady airflow around Nubus cards and the processor heatsink. I'll add that I also fitted thermal compound under the sink at the same time-- the original has none. This alone may have provided the needed results, but I do think the constant airflow was a huge contributor.

 

[retr01]

I'll put a small warning on this topic for a heavily populated IIcx/i/700. The case has vents on top and front of the Nubus slots. Cool air is drawn in over the cards and the hot air is pushed out through the power supply. If using an ATX with variable fan, airflow through the case may not be enough to cool the area around the cards or the processor since the system load or thermister in the ATX supply may not drive the fan fast enough. My Quadra 700 was locking up randomly until I shorted the fan to run at a constant higher speed, thus providing steady airflow around Nubus cards and the processor heatsink. I'll add that I also fitted thermal compound under the sink at the same time-- the original has none. This alone may have provided the needed results, but I do think the constant airflow was a huge contributor.

Hey @joethezombie, thank you for sharing! I am curious, could this be an issue for the compact Macs with internal fans, e.g., SE and SE/30, if those fans such as Noctua were to become variable by adding third yellow wiring from a new ATX?

 

[Kay K.M.Mods]

I'll put a small warning on this topic for a heavily populated IIcx/i/700. The case has vents on top and front of the Nubus slots. Cool air is drawn in over the cards and the hot air is pushed out through the power supply. If using an ATX with variable fan, airflow through the case may not be enough to cool the area around the cards or the processor since the system load or thermister in the ATX supply may not drive the fan fast enough. My Quadra 700 was locking up randomly until I shorted the fan to run at a constant higher speed, thus providing steady airflow around Nubus cards and the processor heatsink. I'll add that I also fitted thermal compound under the sink at the same time-- the original has none. This alone may have provided the needed results, but I do think the constant airflow was a huge contributor.

Look carefully at my schematic. See that the fan is directly connected to 12V so that it is not variable. Thanks

 

[joethezombie]

Absolutely it does! The discussion after specifically mentioning fan speed control prompted the small warning.

Hey @joethezombie, thank you for sharing! I am curious, could this be an issue for the compact Macs with internal fans, e.g., SE and SE/30, if those fans such as Noctua were to become variable by adding third yellow wiring from a new ATX?

Number one priority in the compact macs would be airflow across the flyback. Having an alternative power supply with its own regulated fan would be (most likely) negligible as long as the case fan is still operating at a sufficient volume.

Edited to add: If you are controlling the case fan with the ATX supply, I personally would be weary. I guess it comes down to how happy your are with fan noise vs. longevity of the components. It would be interesting to build a temperature controlled case fan that monitors the heat at the top of the case and observe the fan curve.

 

[retr01]

Yes, @joethezombie, it would be interesting. Some discussion occurred later in this thread on TD about measuring temperature, mounting a sensor, etc.:

https://tinkerdifferent.com/threads/macintosh-se-or-se-30-fan-bracket.976/