The PC Engine Duo-R can be tuned with the potentiometer on the side of the laser.

Clockwise is more powerful, anti-clockwise weaker.

A well tuned laser will pull around 600mA when reading, and an out-of-spec one will pull up to 1.2A as it tries to seek and read the disc.

A successful load should take around 2-3 seconds at max, and the disc spins at medium speed (around 10 rotations a second). It seems almost like it is spinning slowly.

An out of tune laser will spin and stop, or spin very fast.

There are additional tuning potentiometers on the motherboard for tuning DC offset, tracking, focus, gain and PLL.

I haven't reverse engineered which is which yet.

Although each motherboard will be tuned to its own laser and setup, below is a reference point for starting with from a working console.

On a working console this is tuned around center (11k/9k), so the center tab (on the metal top piece) is slightly offset to the left.

On a working console this is tuned around center (11k/9k), so the center tab (on the metal top piece) is slightly offset to the left, just like VR101.

On a working console this is tuned around center (11k/9k), so the center tab (on the metal top piece) is slightly offset to the left, just like VR101.

On a working console this is tuned around center (9k/11k), so the center tab (on the metal top piece) is slightly offset to the right.

This potentiometer is shorted together on the middle and right pin, so only the left to middle is used.

On a working console this is tuned a 544R, so the center tab (on the metal top piece) is slightly offset to the left.

My guess is this is a limit to the laser potentiometer on the laser head, so reducing this (turning it anti-clockwise)