Just wanted to update with a glorious find!
SkipDr works. It really does. I can vouch.
I own 4 games, 2 of which (SimEarth & Super Darius) give me problems. The "pre-boot trick" (mentioned above) really did the trick, but occasionally, the disk would either stop working, hang, lose audio, or begin to give "flapping" noises. This noise is usually associated with CD-Rs & bad discs with bad lenses trying to compensate, as well. So I knew it was only a matter of time until this trick would stop working. My other 2 games would boot up fine, as did audio CDs, so I knew the problem was not with the lens.
These discs could SOMETIMES play on CD players with their Red Book Audio, but as games, they were never dependable, sometimes never getting past the PC Engine CD-Rom screen.
So I looked online for some proper disc scratch fixes & found some (this thread included). I watched videos, read How-To's & went looking for a practical way that wouldn't require expensive professional work. I tried water, alcohol, detailing sprays, toothpaste, CD Repair pastes, rubbing methods, liquid baths, and even contemplated sanding the disc down (DO NOT CONSIDER THIS!). Then I came across a local guy selling a SkipDR classic (not the motorized version, but the hand-crank one). I figured I had reached the bottom of the pit & could not imagine it getting worse, so I called him up & bought it off him.
The mechanism is a wheel that runs round a crank that you attach your damaged CD to (Do a google and see what it looks like). I got myself the SkipDr Classic. It came with a spray, a buffing cloth, the crank machine & a CD tray. I tried SimEarth on first, since this disc NEVER booted up at all. I placed the CD on the SkipDr detachable tray, sprayed on 5 sprits of the provided resurfacing fluid on the data side of the CD, attached the tray to the crank mechanism, and started cranking it. After 1 full rotation, I popped open the tray and sprayed 3 more sprits on the CD, and repeated the process. The crank moves quicker than the discs rotation, allowing for a smooth and steady resurfacing job. After the 2nd round, I popped out the disc, wiped excess moisture from the data side with a micro-fiber cloth, and laid down the disc on a flat surface to buff it back to shininess. I noticed that the disc now had uniformed streaks, perfectly made, going from inside out. It appears the SkipDr's resurfacing wheel is a really, really, really soft abrasive that gently scratches a very thin layer of plastic off the top of the data side, and gives the disc a new surface for the lens to read from. This makes sense, since skips are caused by uneven surfaces caused by scratches, small & big. I must admit, the disc wasn't mirror-like clean, but knowing how most guides say to wipe from inside out, these radial streaks looked like they would be easier for lens lasers to navigate through.
After buffing it enough, I popped it into my Super CD-Rom2 & turned it on. At the startup screen I pressed play/RUN & waited. At this point, I was prepared to see the disc give me an error again & chuck it into the garbage or something.
Then, for the first time ever, it booted up straight away. No joke. It played perfectly after that.
The SkipDr works. Now, the box says that SkipDr cannot remedy deep scratches, and that standard use wear & tear is what it's built for. The motorized & manual versions of the SkipDr both work fine & give the same results, with the motorized one just adding the convenience of saving time & effort.
Both of my discs were relatively scratched & these caused reading problems in my unit. I can't vouch for major scratches, but I can promise that the SkipDr works extremely well to make any discs readable again and is worth a try. My Super Darius is working exceptionally well, with no need for a "pre-boot disc" anymore.
One happy PC Engine owner right here!