Got my childhood Laser 128 back. (c) 1985 VTCL, Made in Hong Kong.
Symptom: System boots to ROM message, but disk doesn't boot, drive seeks forever and disk light stays on forever.
Short Fix: Adjust calibration screw in back of Laser128. Failed. Tried using a cleaning disk. Failed. Dissasembled Laser128 case, removed shield from floppy drive, found that head slid roughly and rails had gunk/old lubricant. Used over-the-counter isopropryl alcohol and q-tips to thoroughly clean the magnetic head, and also the slide rails. Applied Prusa 3D printer lubricant sparingly to slide rails. Head started sliding much better. Re-assembled. Success - the Laser128 now boots all my old disks, sounds MUCH BETTER (much, much more quiet now), and seems to be done having intermittent issues.
Lesson learned: Avoid cleaning disks, take the time to dissassemble your unit. Plain isopropyl works to clean heads. Prusa 3D printer lubricant will hopefully last on these rails. Not sure what type of lubricant it is, but presumably it is a type of lithium grease. Can use ADTPRO transfer feature as a crude/coarse method for dialing in your RPM's.
TLDR Fix: Laser 128 is an Apple IIc clone. I don't know about the disk drive, but assumed the internal 5.25" disk drive on Slot 6 Drive 1 is also some sort of custom/cloned drive. In any case, these Laser 128's have the drive speed adjustment screw (potentiometer presumably) accessible from a hole in the bottom of the case. This is accessible without dissassembling. The only problem was I couldn't run an RPM calibration software, because I couldn't boot the disk!
The next best trick I had was to use the ADTPro and serial cable to a Windows PC. I followed the bootstrap instructions to boot up ADTPRO on the Laser 128. Worked great. Next I tried formatting a disk in the internal drive. It kept failing. So I turned the disk calibration screw all the way clockwise, and all the way counterclockwise, and then tried to turn the screw back to "center" as best as I could guess. And then kept trying to format and kept turning the screw little itsy bitsy clockwise (or counterclockwise) until the disk formatted.
Next I attempted to send a .dsk image from ADTPRO on the windows computer to the Laser 128 and write to the real floppy. Well, it did try to write, and got through successfully, but had lots of write errors. So I kept reformatting the disk and trying the ADTPRO receive/write to floppy disk while making tiny adjustments to the speed calibration screw on the back of the laser 128. I also tried an old cleaning floppy disk I had with isopropyl on it (yes I know, bad form to do this, doesn't work, ill-advised, etc.)
Eventually I was able to get a formatted and programmed disk with no write errors. By the way, the disk I decided to write was MECC Computer Inspector (image available on-line), because MECC Computer Inspector includes a disk speed/RPM test that you can run on your drive with a blank floppy. I was able to boot this newly minted disk, and running the RPM speed test, it gave me 305 RPM. It said the suggested range was like 296 to 302, with an ideal speed of 299. Well I dialed into 299 and... now my disk wouldn't boot. I bootsrapped ADTPRO and I had issues formatting and writing the disk. For whatever reason, it turns out the sweet spot for this Laser 128, according to Computer Inspector, was about 303-305 RPM, which is outside the range. (On an aside, a disk written at too high of an RPM will probably not be readable once you adjust the RPM into range, and vice-a-versa. Someone who understands maths could probably explain it to us some time) . On another aside, I tried Copy II Plus but absolutely could not find an RPM/speed test in there. I tried like 3 or 4 different version of Copy II Plus. Clearly I don't understand that software (dad was the one running Copy][Plus back in the day; I was 8 years old).
Well luckily I happen to have a working Apple IIc and an external Apple IIc disk drive. So I loaded up a separate copy of MECC Computer Inspector and ran the speed test on my Apple IIc drives. I got 297 RPM on the external drive and 298 RPM on the internal drive. Next I took that same exact external drive (that read 297PM on a working Apple IIc), connected it to the Laser128. So the lesson I learned here is the RPM's reported by Comptuer Inspector on my laser 128 aren't exact, because that same drive that reported 297 RPM on an Apple IIc was now reporting abour 302 on my Laser128. So next I dialed in my Laser128 internal drive to 303 and left it as-is. Even though 303 was outside of range, it seems my Laser128 RPM's are reporting high in Computer Inspector.
Still having intermittent write issues at this point though, even with speed presumably dialed in. And drive can only boot some of my disk fleet, not all, and even booting those is intermittent with boot errors. At this point I dissassembled the Laser 128 and removed the shield to the floppy drive, cleaned the magnetic head and slide rails with q-tips and isopropyl (presumably 70% - whatever walgreens sells), and applied Prusa 3D printer lubricant (presumably white lithium grease) to the rails sparingly. Reassembled and now this Laser128 is running like a champion.
I know this is old hat for everyone. Hoping this post might help one fellow Laser 128 owner at some point in the future. Have a nice day and thanks for hosting this website.