Both flippers are weak by the same amount.

Both flippers equally weak: check the flipper supply bridge

Cause: An open diode in the bridge rectifier feeding the flippers, or a cracked joint on it or its filter capacitor (uncommon).

Checks

• Test the bridge and inspect its and the capacitor's connections.

Fix

• Replace the bridge or repair the joints.

Systems

• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b

Related tips

• Weak flipper: worn mechanism
• Solid state flipper does not work: fuses and fuse clips
• Weak flipper on Time Machine and earlier: pitted switch contacts
• Solid state flippers dead, weak or intermittent: clean the switches
• Last Action Hero flippers go weak during multiball: replacement flipper board
• Solid state flipper board versions
• CPU board flipper relay RY1
• Protect the flipper boards when lifting the playfield

Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Two, Clay Harrell (pinrepair.com)