Getting to Red Light Boot (Game Gear VA4)
The VA4/VA5 red light boot circuit operates internally to the ASIC in the same way; however, it has the external circuit on the motherboard wired differently.
The RLB circuit has test points on the VA4/5 board. All test points are on the front bottom right near the cartridge connector.
- M3 is VRef
- M4 is VRes
- M5 is VOnOff
We are making the presumption until proven otherwise that the RLB circuit is the same as VA2 (1-ASIC) boards, which are shown below.
Here are the rules that must pass to get to Red Light Boot, ignoring faulty ICs, traces and so on.
- ASIC VRef is pulled to 0V
- ASIC VOnOff is lower than ASIC VRes
- ASIC VOnOff and VRes are over 0.6V
- ASIC VRef is lower than VRes
In short, VRef is like an inverted battery voltage.
0V is fully charged, and over VRes is totally flat.
Low battery is when VRef is higher than VOnOff (meaning LED goes On and Off flashing to indicate low battery) but not as high as VRes (meaning Reset to put console off).
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.
As there are no known schematics for the VA4 I will explain my tracing done so far to follow the circuit.
VREF on the ASIC (pin 85) is the same as VA2, in that it is connected on the ASIC pin 85 and makes its way to the VREF pin of the power board, while also being pulled down to ground by a 1k resistor R68 (to the left of the cartridge connector). This means this part of the circuit is identical to VA2.
VRES (VReset) on the ASIC (pin 84) goes to R24 and R23. This is the resistor divider network like the VA2 so R23 goes to VBat and R24 goes through R25 to ground forming the voltage divider.
VONF (VOnOff) on the ASIC (pin 83) goes to R23 then to ground, forming the lower half of the resistor divider.
As there are no known schematics for the VA5 I will explain my tracing done so far to follow the circuit.
VREF on the ASIC (pin 85) is the same as VA2, in that it is connected on the ASIC pin 85 and makes its way to the VREF pin of the power board, while also being pulled down to ground by a 1k resistor R54 (right by the ASIC pin). This means this part of the circuit is identical to VA2.
VRES (VReset) on the ASIC (pin 84) goes to R24 and R23. This is the resistor divider network like the VA2 so R23 goes to VBat and R24 goes through R25 to ground forming the voltage divider.
VONF (VOnOff) on the ASIC (pin 83) goes to R23 then to ground, forming the lower half of the resistor divider.
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.
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