Lets try installing a fresh PRAM battery CR2032 3 volt button cell.
Given the age and the fact you store your system for long periods I’m sure the battery is worn out. What can happen is the battery drops below the threshold of being able to support the settings so the settings get messed up. You disconnect the system put it away the battery looses the power altogether! Now with no settings held you plug in your system and it works! But the battery can act like a capacitor so the trickle vampire charge for the power cord charges up the battery but not enough to hold the settings so the settings get corrupted once again! You disconnect the system the store it away and the cycle continues!
[image|2086994]
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=== Update (05/10/2020) ===
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I was hoping the simple fix was all that was needed ;-{
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At this point I’m sure your issue is within the logic board [product|IF169-014] you’ll need to transfer the CPU over.
Lets try installing a fresh PRAM battery CR2032 3 volt button cell.
Given the age and the fact you store your system for long periods I’m sure the battery is worn out. What can happen is the battery drops below the threshold of being able to support the settings so the settings get messed up. You disconnect the system put it away the battery looses the power altogether! Now with no settings held you plug in your system and it works! But the battery can act like a capacitor so the trickle vampire charge for the power cord charges up the battery but not enough to hold the settings so the settings get corrupted once again! You disconnect the system the store it away and the cycle continues!
[image|2086994]