Digital device repair is not a job for the faint hearted.
If you have some experience on this activity and corresponding instruments (millivoltmeter and scope at least 60MHz), I can recommend to you some first steps:
1.Turn XP-10 on and check power supply output voltages +5V and +9V (see power
2.If them are okay, check 20MHz clock at IC11:98, 99 and logic “1” (4-5VDC)
3.Check 24MHz clock presence at IC5:105.
4.If all previous results are okay, turn XP-10 off and check existence of 2.7V-3V
voltage at IC14:28, 20 and IC15:28, 20.
5.If this time results are okay as well, turn XP-10 on and check whether control, data
and address signals at RAMs (see RAM schematic) have normal view.
6.If all seems okay, try to replace RAM chips in turn.
If all this did not help, the device must be transferred to more professional technician for repair.
If results one of these steps are not okay, let me know.