Thanks. I would study the manuals thouroughly first and the circuit diagrams to get to know the unit. Then define the problem you experience and write it down(no power, little bass, no treble and likewise). Then post your issue on diyaudio and the Organ forum defining what the issue is as specifically as possible. After getting some clues you can search on YouTube to see if there are any videos that are relevant to your problem, like changing a resistor, tubes and stuff. Getting a multimeter will be useful to measure and troubleshoot. There are videos on YouTube on how to use the multimeter for troubleshooting audio components.
Some precautions to take before starting:
Never work on the unit while it is connected. Be careful to never touch power supplies and capacitors. Let the unit be switched off for at least 6 hours before working on circuit boards and such. If there is no power in the unit take it to a professional technician to get it worked out.