Technics sx-GA1 organ LCD display low brightness, any idea how to fix ?

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I recently obtained a second hand Technics sx-GA1 organ. Every function is OK except that the brightness of the LCD panel is too low so it is difficult to read what is on the display. The "contrast" on the front panel has effect but it seems that the back lighting is too low. I check the service manual and suspect that there could be two possible areas of fault. (1) the LCD panel has aged. In this case there is no cure except replacement. (2) the a.c. supply for the LCD panel back lighting from the "Inverter" board is too low. This is repairable. However I do not know the normal voltage and frequency of this ac voltage from the "Inverter" supplying the LCD back lighting. Anybody out there knows ? Please help. I was an electronic engineer and so is comfortable to repair circuit boards. Thank you.