Getting to Red Light Boot (Game Gear)
When repairing a game gear after you have recapped the Game Gear and tested your power regulator (original, CleanPower or CleanJuice) are good, you want to get the Game Gear to red light boot.
NOTE: All pin numbers references here are for the 2-ASIC Europe board, so your pins may vary on a Japan version. I have used photos of both the Japan and Europe boards to show where common pads are, but some pads like the 5V rails will differ.
This is the first step to getting the console working. Before anything else will work, you need to ensure you see the red power LED come on when you turn on.
There are only a few known things that prevent the power LED coming on:
- 5V power rail not up to 5V
- VRef pin over 30% of VBat pin (typically Vref pin is 1.28V and VBat is input voltage from power regulator source, usually around 9V
- ASIC not receiving the 5V, VRef or VBat signals due to faulty traces or components
- Power LED or resistor or trace to it broken, so technically system is booting but not showing light
- Valid clock signal
Let us take a look at each step you should follow in order to get to red light boot
Power Rails into Game Gear
Connect your power regulator to the Game Gear and apply power. Then check using a multimeter that you have the following voltages.
VRef should be anything from 0 to 1.8V
VBat should be the input power from the power supply so around 8-9V. If your using a CleanJuice it has special modes that work differently and so VBat will be 5V and VRef will be 0V, once the battery is low it will be 1.4V on VRef.
The 34V rail is not always used (for modern displays like the CleanScreen) and is not required for the console to get to red light boot. However the Game Gear can pull the 34V line low on the original regulator and thereby pulling the 5V rail low preventing boot. So it is sometimes good to just cut the 34V wire in the middle when diagnosing and re-solder it after.
If you have 5V, VRef and VBat all within the range, you should get red light boot, unless you another another fault.
VRef/VBat to ASIC
If you get VRef and VBat into the pins above, there is a chance from there to the ASIC chip there is a break or a fault.
VRef on the connection is a direct connection to pin 30 on the left ASIC chip.
VBat on the connector goes through a resistor-divider network then into pin 32 (VRes) and pin 31 (VOnf). If the connection from the connector to the resistor is broken, or the resistors, capacitor or diode are faulty it could cause the system not to boot.
One test if you have the right power signals on the connector but are not getting red light is to short VRef to ground. That way if the resistor divider network is faulty and producing the wrong divider network then often this allows the console to boot as VRes only needs to be above about 1.6V for the system to boot.
This is obviously just a quick and dirty test and if this works, you should investigate the resistors and also probe the ASIC for the right voltages.
The resistors R50 (9.1k), R51 (1.1k), R52 (3k) and the capacitor C49 and diode D4 are all located on the back at the top left near the power connector cable.
The diode and capacitor are not needed to successfully boot, so if you are having issues you can just remove both of them.
Low Power Flash and Reset
The power on circuit on the Game Gear to get to red light has 2 voltage references. VRes (for RESET, do not boot at all, no red light), and VOnf, which is On/Off meaning the LED flashes on and off, so basically the low battery warning.
The system (typically battery) voltage comes into the console on VBat. Let's say 9V for fully charged batteries. This goes though the voltage divider network on 9.1k, 1.1k and 3k, with VRes tapping off at the top and VOnf below that. Here would be the voltages for a fully charged battery.
Once the input drops to about 6.5 to 7V, the VOnf pin would be lower than the VREF pin of 1.3 to 1.5V, triggering the flashing light.
Once the input drops lower, and the VRes pin is then lower than VRef, the console turns off (so no red light boot).
So the basic rule of thumb is you need to have VRes higher than VRef in order for the system to boot. This is why when we join VRef to ground it means VRes never gets that low so the console never turns off.
If you get your multimeter on the actual ASIC pads above and measure you should get VRes higher than VRef. If so you should be ok. If you are getting 0V on VRes or lower than VRef, confirm your resistors and working, your traces are not broken going to the ASIC and the VRef and VBat coming in on the power connector are correct.
5V Power Rail Good
Another perhaps not so obvious thing to check is that the ASIC is receiving 5V power. You can tell by probing the ASIC corners top left, bottom left, top right, bottom right. It changes between versions but usually you will find near the corners 5V rails are there.
Power LED Output
The ASIC once it receives 5V power, and VRes is higher than VRef, will respond by sinking pin 27 to ground. To test your LED is working correctly you can join the resistor R11 (the one on the opposite side of the board to the LED, right next to the LED pins, to ground. Join the side of the resistor that is furthest away from the LED pins to ground so it is correctly current limited.
Alternatively you can just use your multimeter in Diode mode and put the red and black leads over the LED and it should light up. If it does not light up one way around, try the probes of the multimeter the other way around.
Although incredibly rare, if the ASIC is not receiving a clock signal due to a faulty crystal or supporting components it will not do anything as it cannot run. If you have an oscilloscope you can test the pads of the crystal for a 32Mhz clock signal. If not just inspect the area around the clock components for obvious damage.
There are 2 resistors and a crystal (sometimes the crystal is integrated into the ASIC and you will not see a crystal installed) on one side of the board, and directly underneath are the capacitors.
Out of Reset
The final stage of the system powering up ready to operate is the ASIC sends the !RESET pin to 5V. This reset line is connected to both ASIC chips, the cartridge pin 39 (so a game can sink the pin low to reset the console), and the MPU to bring it out of reset.
Check for 5V on any or all of those pins. If you do not get 5V the ASIC is not running and the system will not work.
Components Needed for Red Light Boot
In order to get red light boot, the only components you need are the 2 ASIC chips (or the single for a 1-ASIC).
You can remove the ASIC RAM, the MPU, the shared MPU RAM, the Op Amp and all LCD circuitry and you will still get to red light boot and the !RESET pin pulled to 5V. This is the first stage in the boot cycle you must achieve.