Zombie Boot (Game Gear)
There is a condition where the Game Gear can have a Zombie effect; during a fairly quick on-off cycle the game can start loading mid-way through a game, at a random point (related to when you turned it off) or not load several times in a row.
These conditions are often caused by two things:
- The system not going into reset when power is removed, and the capacitors are discharging.
- The VREF circuit not being driven hard enough (even the OG power board didn't do this well enough, probably due to aging ASICs the requirement for harder driving is a thing).
- The Static RAM retaining data instead of refreshing it, with low voltage being able to retain previous RAM data, between fast power cycles.
The zombie state can happen to any IC or circuit if the power is not being fully discharged, so the first check is to monitor your 5V rail with a multimeter during power down. This should take less than a second to drop to under 0.5V.
If it takes longer, check the Soft Start / Fast Reset circuit article and fix that.
If the red light boot circuit, specifically the VREF and VRES pins on the ASIC are not correct, then the ASIC may not enter and exit reset properly causing it to retail state information between power cycles.
When first powering back up, VREF should rise to around 1.2V (depending on power board). Then after a short delay drop to 0V. If this VREF is permanently 0V from boot, the ASIC may not get reset from the previous boot cycle.
NOTE: 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.
Check the Getting to Red Light Boot article and confirm all that circuit is working correctly.
If the 5V rail is successfully discharging and the red light boot circuit is working fine, then the next culprit is the Work RAM (Static RAM CXK5864 / MB8464).
When this RAM is faulty it can mistime data, corrupt data, or even retain previous data causing the zombie effect.
The best test for this is just swapping the RAM for new (We sell it).
