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The sk-1 turns itself off when no key or button is pressed for approximately 7 minutes. This is called the auto power off function.

Disabling this function is usefull for those that want to leave their sk-1 unattended for a while and keep it on to remain in the state they left it. 

How does the auto power off work?

By a voltage at PO1 pin 86 that goes Low after 7-8 minutes (schematic can be found in the service manual).

This is the auto power off signal that turns the sk-1 off. The trace leaving this pin needs to be kept High to disable auto power off.

As the cpu works with a ground voltage of -5 volt and 0 volt as a "positive" ,  Low is -5V , High is 0 Volts.
Disconnect PO1 from it's trace , connect the trace at 0 volt instead. No more auto power down.

How can this be done easily?

No need to grind through the trace. There's a jumper that can be disconnected.

PO1 at pin 86 runs along the top of the PCB (solderside, speaker left).
The topmost THIN trace underneeth the Fat trace that leads to a jumper.
Remove this jumper, wire left side to 0 Volt.
For 0V I used the solder point most left/down of the board . At he green and blue wires.

Electri-fire comment: Any remarks or questions can be posted here