Category: Hardware

Mac mini Mock Monitor

I have an old Mac mini that I wanted to use to run a research experiment. Its whole purpose would be to run five versions of the same program millions of times over. I didn’t need a monitor to watch such command-line action, instead I wanted to monitor the experiment remotely using the excellent program screen.

Using a keyboard, monitor and mouse, I installed Fedora and the bits for the experiment, and confirmed it was all working. I then shut down the machine, removed the peripherals, and moved it to its new location. When I powered the machine up again, I was no longer able to SSH back in. So I reversed the moving procedure, hooking up a monitor and mouse, and all was working again. Frustrating!

It turns out that this model of Mac mini (Late 2006) does not boot into its BIOS emulation mode (Boot Camp) without a monitor being attached. Upon searching the Web I found conflicting information about how to solve the problem. Distilling the commonalties of the found suggestions, I determined a simple solution. A single resistor, placed between pins 2 and 7 of a VGA adapter, allowed the computer to boot. The adaptor is the one that came with the Mac mini. The resistor is banded blue-grey-black-gold for 69Ω ± 5% (measured to be 66.7Ω). A photo of the setup is shown below.

A VGA adapter socket on the back of a Mac mini with a 69 ohm resistor placed across pins 2 and 7
A 69Ω resistor placed between pins 2 and 7 of a VGA adapter

If you’ve got any questions, don’t hesitate to ask.

PC Coil Whine

Last month I converted my P4 desktop into a home-theatre PC. Using a soft paint brush I dusted down the old innards till they looked like new, and mounted them into a new case. After powering it up, I was upset to hear a screaming sound coming from my otherwise quiet PC. This would not do for a home-theatre PC.

Listening carefully to the motherboard I noticed two things. Firstly, the pitch corresponded with the workload of the CPU. And secondly, the sound appeared to be coming from the CPU itself!

Doubting my ability to actually hear resonating electrons within the processor, I searched the web for an answer. I found a post that suggested the chokes were responsible, but how?

Alongside the CPU are a couple of inductance coils. These little toroidal coils smooth out the power going to the CPU. My guess is that over time either, the varnish coating on the copper degrades, or the endless heating and cooling lengthens the wire by a tiny amount. Either, or both, of these causes would allow the wire a tiny bit of wriggle room. I further guess that the frequency of the AC power through the coil must be within the range of human hearing. This movement then translates into sound, as each section of the coil succumbs to the changing magnetic field of the section before it. By blowing out the dust I had inadvertently removed the packing that was preventing the coils from vibrating.

Close up photo of a motherboard showing two chokes covered in glue.

Now I’m not sure if my next course of action was the best thing to do, since it’s based on my earlier guesswork, but the PC has been running for nearly two weeks now and all is fine. I coated the chokes in a heap of hot glue, doing my best to contact as much of the surface of the wire as possible. I was pleasantly surprised when it worked!

If you know what actually happens to create the screaming sound and the subsequent course of action to take, then please contact me—I’m curious to know the truth of the matter.

PowerBook G3 PDQ runs without its screen and mic

I am the proud owner of a PowerBook G3 Series laptop (v2, “PDQ”, released September 1998). The “Wallstreet”, as it is known, was an incredible computer in its day. It was one of the first laptops to have everything you could want in a desktop: a 14.1″ active matrix XGA screen (which was bigger than the 15″ desktop monitors of the time), 3D accelerator, 10 base-T ethernet, SCSI, CD-ROM, 56K modem, integrated number-pad, dual-monitor support, TV-out and a PII trouncing G3 processor. Unfortunately in May 2004, one of the screen hinges broke. I was expecting this dreadful event to occur just like it had for many other Wallstreet owners.

Bar graph showing two G3 CPUs outperforming three PII CPUs on a BYTEmark integer test.

Before this time I had bought a new (lighter) G4 PowerBook and was not using the Wallstreet as a portable. Since it must be run with its lid open, there was no room available on my desk to use it with my KVM setup (it wasn’t getting a lot of use). When the hinge broke, and I discovered that the cost of the repair was several times the value of the computer, I wondered if it would run without any lid at all! So I hooked up an external monitor, powered it up, and sat back waiting for the dreaded chime of death (the way in which Macs cry out in pain). I was pleasantly surprised when it booted seamlessly. (It booted in mirror mode. I later switched it to use the external monitor only.)

PowerBook G3 Series without a screen hooked to a KVM.

The PowerBook now lives squished between two shelves that are about 5cm apart. It is hooked to a PS/2 KVM via a generic USB PCMCIA card and Belkin USB-to-PS/2 adapter. An Apple PlainTalk Microphone replaces the one located in its lid. The computer runs as if its screen and microphone were still attached. Running from an external monitor is flawless (it correctly recalls the last monitor and mode used and applies this at startup). The only catch is the lack of a power button on my PS/2 keyboard, and the fact that the said keyboard and PS/2 mouse fail to wake the machine when it’s “asleep”. This means that I have to reach between the shelves for the power button to turn it on, or any key to wake it up. There is also a 10 second wait for the mouse and keyboard to start responding after the computer has been awakened.

If you’ve any questions about this setup, don’t hesitate to ask.