PS One (SCPH-101) disc reading issue

[Technomancer]

Hello folks,

I have an SCPH-101 console with a bit of a strange issue. The unit doesn't want to read discs. Now that in itself isn't all that strange as the lasers in these things often go bad. What is strange, however, is that when I take the laser assembly from this unit and put it in a known working console, it works just fine. Also, when I try the laser assembly from the working unit in this broken one, the disc spins and the laser moves up and down but doesn't really do much else.

One thing I noticed is that it doesn't want to read even audio CDs until I turn the impedance down on the laser pot. Then it will start to read them but with garbled audio. Turning the impedance down even more will get the audio CD to play just fine and it will sometimes even read the PlayStation discs. I also took some voltage measurements from the output of the laser pot (before adjusting the impedance) and it read the same as what I had gotten on the working unit. Obviously I don't really like adjusting those due to the possibility of damaging a perfectly good laser but this problem has me a bit stumped.

Any idea as to what might cause a laser to work on one unit but not another?

*edit* Forgot to include that I can get the unit to read audio CDs and PS1 games with the pot set at around 600ohms.