Yamaha PSR-S750 Internal hardware error

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I have had a Yamaha PSR-S750 keyboard for a long time to my complete satisfaction. However, some time ago while playing the keyboard stopped working. The usual LED lights are on but cannot be changed and the keyboard is completely "dead". Switching on with the on/off button works, switching off does not. The display states: Internal Hardware Error. I have run the test program with over 40 test sessions and it seems to be fine. I also checked the various measuring points with the multimeter according to the Yamaha manual (DM Circuit Board Check Method). The only deviation from the checklist is measuring point 6: Here I measure 1.4 V while the description indicates that it should be 3.3 V. However, the specific description of the possible defective component in this case IC7 in the detailed component diagram does indicate 1.5 V as the output value. Does anyone have an idea how to solve this? Thanks in advance.

Edited by Alex: (Translated by Google Translate)
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