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.
The Red Light Boot circuit (coined by myself as Red Light Boot or RBL) on the Game Gear works by using a comparator inside the ASIC to compare the VRef voltage (current battery level) to VOnof (meaning On Off, flashing LED) and VRes (meaning Reset).
- If VRef is higher than VRes then the system is held in reset and no red light comes on.
- If VRes or VOnof are also lower than about 0.6V the ASIC treats it as faulted and remains in reset too
- If VRef is lower than VRes but higher than VOnof then the console comes out of reset but the red LED will flash indicating low battery
- If VRef is lower than VOnoff then the red light remains on and solid.
To summarise this means VRef acts like a battery level indicator in reverse; the higher the voltage, the lower the battery level. All voltage is relative to VBat, and the example shows CleanJuice typical voltages.
As when the battery is not present or lower than the voltages needed to generate VRef the ASIC internally pulls the VRef pin higher than Vres, keeping the console in reset until the power board pulls VRef low.
You can also pull VRef up to 2.5V or even 5V to force a reset from the power board for a clean reset.
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 higher than VRes
- VRes or VOnof lower than 0.6V
- ASIC not receiving the 5V, VRef, VRes or VOnof 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
In short, if you are not getting red light boot its most commonly a broken trace between the Vref pin to ASIC, the Vbat pin to resistor, or resistors to VOnof/VRes pins, or faulty capacitor or diode.
Let's test those all quickly.
Components Needed for RLB
It's worth noting that audio ICs, every aluminium capacitor, the LCD, MPU, Work RAM nor Video RAM or main crystal are involved or even needed to be soldered on the board to get to red light boot. Don't waste your time on those until you get red light.
Here are all the checks in a single image you should be able to quickly follow. Just follow the check list.
Make sure you have continuity from your power supplies ground (while connected through the harness), to the ASIC ground, and the VBat circuit ground.
If any of them are broken, join them back to the power supplies ground with a wire.
Connect your power board 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 depending on power board, and must be lower than VRes to come out of reset.
VBat should be the input power from the power supply so around 8-9V for original power board and 5V for CleanJuice.
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.
The VREF pin actually wants to be driven fairly hard. The original power supply, and older CleanJuice mimicked the original power board. However, both are technically not as good as they could be.
The VREF pin in order to reset the Game Gear wants to be driven from a 5V rail (so the 5V output) via a 512R resistor. Internally the Game Gear tries to drive this pin low itself and the job of the power board to reset it is to pull it high.
You want to see around 3V on the VREF on boot to get a good hard reset. This allows for a super-fast on/off of the console without issue.
Newer CleanJuice from June 2024 now come with this strong drive circuit.
To test if you have the VREF issue, cut the VREF wire between the Game Gear and power board, and solder a 512R resistor onto the VREF wire / pad of the Game Gear. Leave the resistor floating in the air, turn the console on. Now just tap the resistor to the 5V rail to force a reset of the console. You should be able to reset it rapidly by tapping the resistor to the 5V rail.
If that test works, but the console does not work the same with your power board, it is likely due to a weak VREF driver.
Measure continuity from Vref pin of the power ribbon to Vref pin of ASIC (2-ASIC pin 30, 1-ASIC pin 65).
I like to test directly from power board to ASIC so the entire flow of VRef from source to destination is tested.
Next we want to test the full resistor network, traces, capacitor and diode all at the same time.
If the network is working, we will get voltages (depending on VBat voltage) starting at the VBat voltage then dividing down to two smaller values.
Turn on the power to the system, then measure voltage DC using your multimeter, and see if you get similar voltages here.
The diode and capacitor are not needed to successfully boot, so if you are having issues you can just remove both of them.
In order to come out of reset, VRef is typically 0V for CleanJuice, or basically lower than VRes in order to prevent holding in reset.
Confirm your VRef is lower than VRes otherwise your power board is outputting "low power" to keep the console in reset.
A quick way to test if your VBat circuit is bad, and bypass it all together is to simply short VRef to ground, as the ASIC pulls up VRef to 3.6V internally.
Now disconnect the power board, and apply 5V directly to the 5V pin.
You cannot short VRef to ground and power the console using the original power (you can on CleanJuice or CleanPower) due to how the circuits work.
So you will need to use a bench power supply to inject 5V or use a CleanJuice or CleanPower.
So long as you have continuity from the VRef pin to ASIC, this test will bypass the VBat circuit. If your console gets to Red Light Boot doing this, but not without the short, you have an issue on your VBat circuit.
Make sure your ASIC is receiving the 5V power from the system by measuring the 5V pins on the ASIC.
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 o all of those pins. If you do not get 5V the ASIC is not running and the system will not work.
If the ASIC receives the 5V and all VBat, VRes and VOnof, and those voltages are within range (VRes/VOnof greater than 0.6V and VRef higher than VRes) the ASIC should come out of reset.
Measure the !RESET pin to confirm it is 5V.
If !RESET is 0V (still in reset), then typically this means you have a dead ASIC (confirm by checking the ASIC Dead Test for that), or shorts somewhere on the ASIC pins or passive components connected to some vital lines.
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.
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.
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.
