Then recently, while watching a movie, the PS3 beeped and turned off, leaving a blinking power light. Subsequent attempts to unplug it and power it back off yield the same result. Well now what? While the price of a new system isn't that bad with the release of a new generation of consoles, I still payed a lot for the system I have when I bought it. Not to mention all accumulated files and progress stored on the drive which is not as easy to recover as one would expect. Off to the internet!
After a little searching around I found a solution. Apparently the CPU and/or the GPU can heat themselves up so much that they can weaken their solder joints. I believe they're BGA packages, so you can't bust out the soldering iron. Fortunately, YouTube has a solution:
Watch PS3 Red Light Fix on YouTube
While first using the system, I had a small desk fan blowing across the system to force a little more air over the heatsink for the PS3. After awhile I got a little more confident in the fix and stopped using the fan. So one night while watching Netflix I fell asleep, and woke up later..... only to have the flashing red light again... Well, time to pull it apart and reflow again. What I need is a fan that turns on and off with the PS3, and while we're at it, speeds up when the system gets hotter. And a circuit that will make this work.
Alright, the desk fan is out. It's too big and clunky, and yes it could probably just be turned on and off with the PS3 via a relay, but what fun is that? Now on to what I have laying around. How about a pair of 92mm case fans? These Nidec Beta V's (TA350DC M35105) fans are rated up to 5,700 RPM and 1.8A. I'm going to stress at this point that I have no experience driving fans like these. Sure I've driven some basic DC motors by varying the voltage or using a PWM, but this required a little more thought. A PWM drive is the starting point.
OK, the fans are taken care of, but what about a heat sensor? Well I don't have any thermistors and couldn't buy any locally. But I did recall from my engineering courses that semiconductor devices have a negative temperature coefficient. Sure enough, after a little research, I found that a silicon diode drop will vary around -2mV per °C. This means that if your diode drops 600mV at room temperature, when heated 10°C above ambient, it will only drop 580mV. And this behavior is pretty linear across temperature and consistent from part to part. And yes, resistors also have a positive temperature coefficient, but it never crossed my mind to use one. The change in voltage will be dependent upon the applied voltage for one (the voltage will proportionally change the same regardless the applied voltage, but it's a matter of dealing with uV or mV for actual change in voltage; larger applied voltage = larger observable change). Also, the temp coefficients can be pretty small with resistors, and I have no idea what they are for the ones I have.
Now we've got fans and a candidate for a temperature sensor, how are we gonna power our circuit and get it to turn off and on? Well the PS3 is really just a computer packed to look like a gaming system. It has to support various configurations and use some modular componentry such as the hard drive, optical drive, USB, wireless, Bluetooth, etc. And like a PC, it has a dedicated power supply module that is similar to ATX supplies. When the system is off there is 5V standby power to illuminate an LED and operate a soft switch circuit. When the appropriate signal is applied to the power supply, it turns on the main 12V rail and the PS3 fires up. All we have to do is tie into the 12V portion of the supply.
