I've received the dental mirror, I watched the upper head, I also was able to take a better picture of the lower one.
The only thing that sounds wrong to me it's that black dot where I made a red circle:

As a desperate measure, should I try with a cotton swab wet in acetone and then give another ipa cleaning?

Update: after another cleaning process, this time with imd (clean heads 9 pass) I retried the floppies I received yesterday, apparently they now work fine 3 out of 4, i'm still somewhat doubtful, how is it possible that now it reads floppy that were non working before?
Also the black mark in the lower head is gone.

Yes, those black specks is most likely your problem. And notice the upper head has a similer one, right opposite the lower head, there is a dark spot near the line that is the head coil. Any floppy would be pinched and scraped by those two things, you need to get rid of both (if you haven't already). A cotton swab soaked in IPA and gentle scrubbing, rinse and repeat as IPA dries off, it will come off eventually. It's dried and hardened by now I guess so that's both why it's hard to remove and why it causes damage to floppies so quickly.

As for why floppies read now - floppies are actually quite reliable, even deep grooves in the magnetic material are not going to kill them right away if the grooves are narrow and clean. But the distance between head and the magnetic material is very critical, that's why the upper head has a spring on it - to add clamping force. Any dirt on the surfaces I've mentioned can add a fraction of mm air gap and that already degrades the signal. With old, faded floppies that might even mean they won't read at all. With clean surfaces the head is again in proper contact with the surface, no gap, and it works better now - yes, even with the damage.

EDIT: Forgot to add: NO ACETONE OR OTHER AGGRESSIVE SOLVENTS. Just high % IPA and patience.

This is a better close-up of the head: https://upload.wikimedia.org/wikipedia/common … gnetic_Head.jpg
It's older type (with more primitive suspension) but most likely the head itself is closer to what you have in that 360K drive. Notice clean lines, no dark spots of any kind near them (or on the rest for opposite head). This is what it should look like when clean.

Thank you for your assistance.
The damaged disks I do not know if it was because of the floppy drive or because they were bad in first place) they get worse and worse.
But with IMD I was able to fully make an image and it's fully working, no damaged sector and so on.
So I suppose the heads are good now, I should just be aware of what floppies I will use.
I was also able to read a 1.2mb floppy disk so I can confirm it's a 1.2mb drive.

So I ended up having enough 5.25 drives, since I bought 2 of them as broken and one was actually working while the second has been repaired by a friend.
I have the no name drive that gave me so many troubles up there.
A Mitsubishi MF504C-318M which after a clean works fine.
Epson SD-600 which needed a repair to the spring and now works like a charme.

They are all able to read 1.2mb disks. The no name is the one I like least because it's yellowed and it hasn't the spring which kick of the floppy when you unlock it, while Epson and Mitsubishi has it.
I readed about the Teac FD-55GFR which had the highest compatibility (reading) even with older disks. But info about those models are somewhat scarce instead.

Which ones should I keep? One will go on my 486 build for sure.

The one you had problems with is an Alps, looks to be made on licence (or it's just a clone?) from Shugart Associates because it's very similar to their SA455/465 series. And these were early half-height models that did not eject the floppy as you noticed.

I'd say it's matter of preference. What do you need, exactly? Looks? As in, clean - go for the clean one. Old look or specific color to match a case? Pick the yellow one or the oldest one. Feel? What do you like (apparently not the lack o eject, so I guess Alps is out)?
Some drives are more quiet than others. More modern (mid-90') drives use less power (just one or two SMD chips), and usually are easier to service mechanically but are not really repairable electronics-wise. You'd need to swap entire PCBs from a donor drive instead. But they usually offer superior heads and amplifiers, can read weak floppies better. Or maybe you want the sounds?

If you want reliability then newer drives are better (except the very last models from 3.5" family, those were meant to be cheap and were assembled with little care to detail and a lot of cost cutting). PC floppy drives rarely die from overuse, and even diry ones can be cleaned and repaired, but obviously clean ones that had little use should be higher on your list.

As for TEACs, I like them, easy to service, pretty common so parts can be swapped, but there are some differences between various generations. Not all of them are indentical, for example later models have different heads. Also TEACs do have their own issues like the "sponges" on the clamping arm falling apart. Once those rip off or compress peremanently there isn't enough pressure applied on the top of the floppy sleeve - that can result in vibrations that generate noise, and sometimes affect the uppper head pressure and how well it reads. TEACs are nice but they are not peferct drives.

Of all these that SD-600 is probably the newest model, but I'm not quite sure when Epson started manufacturing that series. If in doubt (and when looking for newer models) look at the head cables. Newer models will have FFCs (flat flex cables) instead of the older round ones. These are more fragile so be careful cleaning around them but they come with newer heads, and most likely also more modern chips on the PCB. That's not to say older heads are considerably worse, a HD drive will have HD head, there isn't that much difference between them (unlike very old SD/DD heads).

Deunan wrote on 2023-04-01, 22:30:

The one you had problems with is an Alps, looks to be made on licence (or it's just a clone?) from Shugart Associates because it […]
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The one you had problems with is an Alps, looks to be made on licence (or it's just a clone?) from Shugart Associates because it's very similar to their SA455/465 series. And these were early half-height models that did not eject the floppy as you noticed.

I'd say it's matter of preference. What do you need, exactly? Looks? As in, clean - go for the clean one. Old look or specific color to match a case? Pick the yellow one or the oldest one. Feel? What do you like (apparently not the lack o eject, so I guess Alps is out)?
Some drives are more quiet than others. More modern (mid-90') drives use less power (just one or two SMD chips), and usually are easier to service mechanically but are not really repairable electronics-wise. You'd need to swap entire PCBs from a donor drive instead. But they usually offer superior heads and amplifiers, can read weak floppies better. Or maybe you want the sounds?

If you want reliability then newer drives are better (except the very last models from 3.5" family, those were meant to be cheap and were assembled with little care to detail and a lot of cost cutting). PC floppy drives rarely die from overuse, and even diry ones can be cleaned and repaired, but obviously clean ones that had little use should be higher on your list.

As for TEACs, I like them, easy to service, pretty common so parts can be swapped, but there are some differences between various generations. Not all of them are indentical, for example later models have different heads. Also TEACs do have their own issues like the "sponges" on the clamping arm falling apart. Once those rip off or compress peremanently there isn't enough pressure applied on the top of the floppy sleeve - that can result in vibrations that generate noise, and sometimes affect the uppper head pressure and how well it reads. TEACs are nice but they are not peferct drives.

Of all these that SD-600 is probably the newest model, but I'm not quite sure when Epson started manufacturing that series. If in doubt (and when looking for newer models) look at the head cables. Newer models will have FFCs (flat flex cables) instead of the older round ones. These are more fragile so be careful cleaning around them but they come with newer heads, and most likely also more modern chips on the PCB. That's not to say older heads are considerably worse, a HD drive will have HD head, there isn't that much difference between them (unlike very old SD/DD heads).

Thank you very much for your complete and exhaustive answer.
I dislike the "Alps" for some reasons, I'd say that the spring which doesn't eject the drive is the last one. The spring to keep the floppy in place when inserted is somewhat silly sometimes it just doesn't stay in place. I tried to put some new lubes that helped a bit but still after turning it down sometimes it gets back in original position. Also it makes a acute sound when reading a floppy, it's also the one more yellowed of the lot.

The Mitsubishi MF504C-318M is fine, nice loading mechanism, nice sound when seeking, reading. I got a weird result with imd when I tried the track reading but i'm not so confident with the use of the program so I tried to read a full 1.2mb disk and since it copied all to the hard drive I suppose it works fine. The color is somewhat different from the beige case looking case i'm going to use, this one is more greyish but that's not so important. What made me think is that the spring to lock the floppy gets down even if there is no floppy inside, do you think is it intended?

The Epson was again ok, it had an issue to keep the spring in place (the previous owner probably forced the lock mechanism to lower the lever without a disk inside and the plastic part has broken), nice sound and nice color, other than this issue it was the one stored in best conditions.

That being said what I care more is longevity, I won't use it that much but I'd like to have a realiable drive and with chance of reading most of 5.25 different floppies (40\80 tracks).

As a side note I took a video of the "alps": https://youtu.be/PMXHTTr5J-E

Nemo1985 wrote on 2023-04-01, 22:44:

What made me think is that the spring to lock the floppy gets down even if there is no floppy inside, do you think is it intended?

Some drives can be closed with no floppy inside, some cannot. And, as you already noticed, there are idiots around that forcibly close empty drives which damages the lock-out mechanism (which is often just a piece of plastic that breaks).
In general this lock-out is nothing critical, you don't want heads to bang against each other but that can only happen with pretty severe vertical vibrations - like during transport (and maybe earthquakes). In open position there is no chance of the upper head falling on the lower one, only when closed (without a floppy) can that be a problem. To prevent that it's always best to insert a special paper shim (or an old floppy) and lock the drive closed for transport. Especially on drives that have head loading solenoid.

As for the problems with locking on that Alps - on SA drives the locking lever is held in place by two set screws in its collar. If Alps uses similar method make sure the lever is not cracked and the screws are positioned properly over the shaft (there should be a flat cutout at the end) and are not loose. It could also be that the same gorilla that broke the lock-out plastic also damaged the plastic part of the clamping mechanism...