Bought a DVL-919 to replace my DVL-909 that I stupidly broke (although I can at least blame part of this on the fact that Pioneer didn't put hardly any adjustment instructions into their 909 service manual), but it arrived with side B playback problems similar to this thread:
[DVL-909] B side playing issueThanks to Kurtis's posts in that thread, I correctly surmised that the issue was due to the side B centering, and was able to fix the player by making adjustments as shown in the 919's service manual.
I used an oscilloscope, a normal CAV disc, and a Harmony with the service remote codes, but the service remote wasn't really needed.
All I had to do was pause on a random frame with some bright objects (not sure if the bright objects were needed), and make adjustments as in "Spindle Motor Centering Adjustment for Side B" in the 919 service manual by turning the adjustment screw until the signal was as high as I could get it, only took a couple tries.
To reiterate, I don't think I really needed to put the player into test mode and use the service remote, but I probably couldn't make the adjustments correctly without the oscilloscope, as the signal would usually change slightly just by pulling the screwdriver from the adjustment screw, and the onscreen picture didn't seem to change at all while making the adjustments.
Didn't pay too much for the oscilloscope, as it was a used Hitachi CRT scope from the 90's. Takes up a good bit of space though.
So for anyone who wants to try making LD adjustments without going in blind, I'd heartily recommend getting an oscilloscope and learning how to use it, they can certainly be confusing but I was able to get the hang of it by watching YouTube videos and just messing around with all the controls.
Now maybe I can try adjusting the laser on my Turbo Duo, it's been recapped and adjusted by a reputable retro game modder already, but CD audio has started to cut out randomly. Maybe there's some way to hook up the scope to a MISTer and and play Vectrex games or something, too.