IIcx, IIci, Q700 (and more) Stealth Power Supply

[Garrett]

As promised, I'm starting a thread for my tinkering with upgrading the internals of the well-known and somewhat hated power supplies for the Mac II/Quadra 650/700 desktops. Like many of you, I have a few of these that are dead as a doornail. For the rebuild, I've ordered three 300W Seasonic units. Voltages and power ratings seem to be close enough to the OEM PSU so we should be in good shape there. I took a little gamble on the size, but it looks like things will fit. The PCB on the Seasonic is a little narrower than the width of the ASTEC case - yay!

The circuit and respective parts to invert the on/off signal to trigger the Seasonic are below. I haven't ordered any of these parts yet. I wanted to test the power supply itself by jumping the trigger wire to start with. Once operation is confirmed, I'll move onto stage two and build the inverter. More to come.

 

[Garrett]

My DigiKey order containing the resistors and transistors has arrived, so I focused a little more time on building the power supply. I started by taking apart the Seasonic. Pretty easy - just a few screws and the board was out. I did have to desolder the AC input lines. Once the new Seasonic board was isolated, I decided to desolder the wires (3.3V, 5V, GND, etc). This was a huge time drain, as I forgot about how difficult lead-free solder is to work with. It took so much flux, heat, and time to get all the wires out! Next time I am going to chop the ends off and solder the old wires to the new ones (leaving the PCB alone).

I then took apart the old IIci PSU. Tossed all the internals with the exception of the main connector, which I didn't cut, but desoldered as well.

This is kind of where things stand today. I still need to land all the wiring and build my soft power inverter circuit. For fun, I played around with a few different ways to mount the PCB inside the original enclosure. It's tighter than I anticipated! I bought a kit with various length standoffs, but I think what I'll end up doing is hanging it upside-down from the top. That should yield the most airflow through the rest of the case and allow for the ferrite bead on the connector to have room. Yes, I know I should paint the metal enclosure...