@WildW:
It is strange that it only happens during games.
What the other people described sounds more like the normal issues you can get different adapters and cards because how the A1200 LED circuit works in combination with incorrectly designed adapters/cards.
The /ACTIVITY pin on an IDE-bus is supposed to be a active low shared pin - pulled high to +5V by a resistor and driven to ~0V on activity by open collector/drain drivers in the IDE devices. The open collector/drain drivers will only let current flow when driving the signal low, which is why it can be shared by several devices.
The A600/A1200(/A4000) IDE activity LED circuit is controlled by a transistor which will start lighting the LED at ~5V-0.7V=4.3V. On the motherboard, there is also the required 10kOhm pullup resistor to +5V.
There are several different devices which causes problems with the above LED circuit, where it is always lit or always flashing rapidly.
Examples:
- The newer version of the IDE<->SD-card-adapters has a 3.3V push-pull driver (incorrect choice, not even safe for it to share the pin with other device) for the /ACTIVITY signal which will overpower the 10kOhm pullup resistor on the motherboard completely and the signal will be at ~3.3V when inactive and ~0V when active. For more details on how to fix this, see:
http://megaburken.net/~patrik/Amiga%...D%20LED%20Fix/
- SATA/mSATA<->IDE-adapters usually has the correct open drain/collector driver for the /ACTIVITY signal, but for some reason has a 10kOhm pullup resistor to +3.3V. This will fight with the motherboard +5V pullup resistor and cause the signal to end up somewhere between 5V and 3.3V (4.3V) when inactive - more or less exactly around the level where the motherboard transistor will light the LED, making it flicker rapidly.
Remove this resistor to solve the problem: backtrace the /ACTIVITY pin (pin 39) on the adapter to find the resistor connected to the onboard 3.3V supply at the other end.