A320 OPC alternate braking problem

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Hi,

i would like to ask what are the possible reason why the alternate braking system failed during OPC (operational check)

on the panel 400VU

if you push the brake pedals on CAPT or F/O side slowly,

as per AMM, the pressure shown at full pedal movement is
between 2400psi and 2700psi..

but it indicates only at 500psi..

what are the possible reasons? and what are the possible solutions
to resolve this problem..


thanks