A looong post and you didn't provide any actual details. Please select:
a) SCSI driver doesn't see it on the bus
b) driver loads but no spin
c) spins but doesn't read
Make sure to test with a known good CD-ROM (as in, not a CD-R, RW, or anything recordable).

Also, since there are no photos of the front, if there is a play button please try CD-DA playback.

Deunan wrote on 2023-07-01, 21:37:

A looong post and you didn't provide any actual details. Please select: a) SCSI driver doesn't see it on the bus b) driver loads […]
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A looong post and you didn't provide any actual details. Please select:
a) SCSI driver doesn't see it on the bus
b) driver loads but no spin
c) spins but doesn't read
Make sure to test with a known good CD-ROM (as in, not a CD-R, RW, or anything recordable).

Also, since there are no photos of the front, if there is a play button please try CD-DA playback.

I'm sorry but I answered every one of those questions and covered every one of those points. That is why the post was long.

If you aren't going to read it, you don't have to read it, but don't say that I didn't provide details and then ask about every single thing I covered in my post. Yeesh.

Only thing not mentioned was that there is no play button, but I did try CD audio (as mentioned).

EDIT: I bolded the part that covers everything you asked. The rest is there to answer most other questions someone might ask about this.

Guilty as charged, I've only read half of it, and missed those bits. I suppose I shouldn't criticize your writing style considering my poor job at reading comprehension but had you stated these things in the first paragraph, and only then went on a trip down memory lane, we probably wouldn't be discussing that now.

Anyway, I'm going to assume it spins up. And BTW you can confirm that by briefly operating the drive with no cover, no need to guess. Usually there's a specific noise when the head tries to adjust focus to catch the track, but can't, the drive will give up after a while and stop spinning. If there is no attempt to focus it's usually the driver IC that's toast. Sadly it's not exactly a good method of telling because there's also fine tracking and that's silent, plus one of the coils can be shorted for example. It's not always a "weak laser" and frankly a proper diagnosis requires some scope probing.

You can try the pots, I would first just try to work them but return to original position (sometimes the pot wiper is wonky). For experimenting get a CD-ROM you won't miss because once you start messing with the pots you might cause the lens hitting the surface of the disk.

EDIT: How long does it take for the drive to spin down? If there is no weird noise that could also mean the head is actually following the track. In that case if the spin-down time is pretty long, say about 20 to 30 seconds, the problem might be with software and not hardware.

I see a ton if electrolytic caps on there. Replace them. If the drive appears functional but just doesn't recognize/read disks, that's usually the issue. Some people will try cranking up the laser power, which is hit or miss and only burns out the laser diode. (cough xbox drives) From much experience, don't touch the potentiometers..

Which game disks did you try ? Try to find the oldest retail cd disk you have, and try an original Win95 cd if you have it. The electronics is late 93 so a 1994 or 1995 cd would be best to try.....just a suggestion
From my experience way backwhen found that a lot of the 2x and 4x drives were very media picky. Has to do with the laser color and cd media color (even silver looking disks have a color hue that is barely visible to the eye).

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wiretap wrote on 2023-07-01, 22:44:

I see a ton if electrolytic caps on there. Replace them. If the drive appears functional but just doesn't recognize/read disks, that's usually the issue. Some people will try cranking up the laser power, which is hit or miss and only burns out the laser diode. (cough xbox drives) From much experience, don't touch the potentiometers..

Thanks for the advice, I appreciate it. That is a LOT of caps to replace to get a 2x CDROM working, for sure.

Deunan wrote on 2023-07-01, 22:28:

Guilty as charged, I've only read half of it, and missed those bits. I suppose I shouldn't criticize your writing style considering my poor job at reading comprehension but had you stated these things in the first paragraph, and only then went on a trip down memory lane, we probably wouldn't be discussing that now.

Well, yes, if I'd known the exact questions that Deunan would ask and put the answers to those in the portion of my post that Deunan would actually read, I'm sure Deunan wouldn't have felt that he had to throw snark at me for not answering those questions in the way he'd prefer. I will try to do better in the future. 🤣

Deunan wrote on 2023-07-01, 22:28:

Anyway, I'm going to assume it spins up. And BTW you can confirm that by briefly operating the drive with no cover, no need to guess. Usually there's a specific noise when the head tries to adjust focus to catch the track, but can't, the drive will give up after a while and stop spinning. If there is no attempt to focus it's usually the driver IC that's toast. Sadly it's not exactly a good method of telling because there's also fine tracking and that's silent, plus one of the coils can be shorted for example. It's not always a "weak laser" and frankly a proper diagnosis requires some scope probing.

You can try the pots, I would first just try to work them but return to original position (sometimes the pot wiper is wonky). For experimenting get a CD-ROM you won't miss because once you start messing with the pots you might cause the lens hitting the surface of the disk.

EDIT: How long does it take for the drive to spin down? If there is no weird noise that could also mean the head is actually following the track. In that case if the spin-down time is pretty long, say about 20 to 30 seconds, the problem might be with software and not hardware.

I appreciate all the tips. I haven't been running the drive with the cover off because I have just always been in the habit of keeping optical drives covered due to the laser. It seems logical that it isn't powerful enough to cause eye damage, but being infrared and 30 years old I didn't want to take a gamble with something I don't fully understand.

Since my first post I did see the disk spin though. I was testing some things and powered off the system right after inserting and attempting to access the disk, and when I lifted the drive cover the disk was still spinning down.

I will keep tinkering with it, and I'll weigh my options.

Thanks again guys.

Also, I did find a thread on another forum where people were adjusting the pots on different NEC CD-ROM drives:
https://www.pcenginefans.com/forum/index.php?topic=14675.0
Totally different model, but it does have pots labeled VR101-VR105 (105 is a few inches from the others on mine). I'm sure they're very different though, and I'm inclined to think that bad components are the culprit with this one.

Horun wrote on 2023-07-01, 23:10:

Which game disks did you try ? Try to find the oldest retail cd disk you have, and try an original Win95 cd if you have it. The electronics is late 93 so a 1994 or 1995 cd would be best to try.....just a suggestion
From my experience way backwhen found that a lot of the 2x and 4x drives were very media picky. Has to do with the laser color and cd media color (even silver looking disks have a color hue that is barely visible to the eye).

Yeah, I've had trouble with media compatibility in the past too. I tried the Papyrus Nascar Racing CD from 1994 and Queensryche Promised Land PC game from 1996, as well as audio CDs without data tracks. All original disks.

Shouldn't an optical disk laser be visible with a digital camera? I know that other infrared sources, like a TV remote LED, are visible with my phone camera, but a little while ago I decided to try looking for signs of life inside this thing and saw absolutely nothing. I looked in the front with the bezel off (through my phone camera of course) and looked at the top of the disk, but there was no visible glow or light of any kind. Tried it right after inserting a disk when there is a bit of noise from the drive and tried it when executing a command in DOS.

SMD electrolytics are known to fail in many of these early CD-ROM drives. In your case they look fine, but maybe it's worth it to pull out a couple to test them, maybe they've dried out.

If the drive was not frequently used, I wouldn't expect the laser diode to have failed, but you never know. I have 3 double speed drives and 3 quad speed drives, they all seem very reliable and work perfectly to this day, with the only issue of sometimes not wanting to read CD-R media. I've had way more laser failures on later drives, in particular I've seen many of those CD/CD-RW combos from the early '00s drop like flies!

Oscilloscope probing laser output and voltage rails (directly on big chips inside cdrom) would give us tons of data.
not being able to even sync with AudioCD means its really bad, either burned out laser _or_ very noisy/saggy supply.

The early CDROM drives were built fairly well compared to later IDE and SATA models (which is why they were expensive).

Generally, I would bet some SMD capacitors are out of spec.

if you have an ESR meter, you can do in-circuit measurements on these SMD caps. this isn't necessarily accurate of course but when checking all of them it can give you a general idea of what state the caps are in or even identify certain bad caps.