Marantz MA-5 amplifier level led indicator alignement

Good morning,
I own a pair of Maranz MA-5 amplifiers. The level indicator LEDs on one amplifier only light up at fairly high volumes. Does anyone know how to adjust the settings? Unfortunately, I don't have a service manual and I couldn't find any information about it. Thank you very much.
 

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We really need to see a complete circuit for this. I assume there is no meter sensitivity switch anywhere?

Have these worked OK in the past and this is a genuine failure, or are the amps an acquisition with an unknown history?