Dockstar modding
While the Dockstar is a great platform, I couldn't help modifying it a bit. First of all, it doesn't have a RTC, which normally gets used for timekeeping when the device is off. Actually, the processor itself does have one, but the Dockstar PCB doesn't have the required 32KHz crystal or the backup battery. The effect is that every time the Dockstar reboots, it thinks it lives somewhere in the past decade. While I could fix that problem in software by synchronizing the Linux clock to NTP, I wanted the device to have the correct date in time even without a network connection.
Enabling the RTC in the Dockstar already has been done by some people, and there's some information about that on the German Mikrokontroller.net forums. Basically, you have to desolder 3 SMD 0402 resistors, replace them with capacitors, add an 1M resistor and crystal. Then you have to add a 1.5-1.8V backup voltage and you're done.
This is my attempt at implementing everything. A 3V lithium-battery in series with
a diode supplies the 1.6V backup power and the 32KHz crystal is placed next to the main
crystal. As you can see, I've also added a bit of cooling to the CPU and RAM.
Super-close-up-mode enable! Underneath the wires of the watch crystal are 2
0603-sized capacitors and the 1Mohm resistor.
There was another thing that sortta worried me: the power supply. I had decided to keep the original MacSE power supply in place: it had enough burn-in and as far as I knew the quality of these PSUs is good. They do come from another era: when the MacSE was designed, most of the logic ran on 5V instead of the 3.3V, 1.8V and even lower voltages that are in use in modern technology. That meant the power supply could supply lots of well-regulated 5V power, but not as much current on the 12V line. If I could lower the load on the 12V line by moving load to the 5V, that would probably increase stability and efficiency of the PSU.
One of the things that do run on 5V is the complete USB-bus. Power for that is generated
internally on the PCB of the Dockstar: there's a little DC-DC-converter on-board which
does the power conversion between the incoming 12V and the outgoing 5V. I could locate
the IC that was reponsible for that relatively easy by back-tracking the 5V line to the
USB ports. Disabling it was even easier: just remove one single inductor. In place of
that inductor, I soldered two capacitors from the 5V-line to ground (for stabilization.)
A connection to a Molex-connector finished the job and made connecting the Dockstar to
the MacSE PSU a bit easier.