Need more information !
Are you using a standard full version "vintage" 5 connector floppy cable with twist near the end for the 3.5" ? like here: http://www.nullmodem.com/Floppy.htm
If using a standard old floppy cable like that with a twist then yes both drives should be set as DS1 and the 3.5" A should be at the end of cable with the 5.25" B in the middle (the typical method)...
then set BIOS for A to the 3.5" and B to the 5.25".
What motherboard or controller are you using ?

Yes, I'm using that cable and the 3.5 was connected at the end after the twist. 5.25 connector is in the middle. Also bios was set like you said.

But even with the 5.25 set as DS1, I couldn't read anything.

The motherboard is a Msi ms-6524.

Just to be sure, have you tested the 5.25in FDD when on its own?

Yes, only the 5.25'' set as A drive and behaviour is the same.

Maybe the jumpers need to be set different than most on your Panasonic, will check for jumper docs after work or maybe someone has them.....

Jumper settings.

And I have perhaps a news, not good tho. Maybe it's the spin motor that is leaving on me. It spins when I insert the disk for a little and nothing at all when I try to read.

Yeah just found that same DOC, it appears DS2 is default not DS1. Which makes sense when the 5.25" is B drive attached before the twist in the cable.

So do I should leave it as DS2?

I maybe can find other 5.25'' floppies at work, I will search today.

Yes, leave is as DS2. Make sure you have TM jumper closed. Also, are the floppies formatted? Is the format standard 1.2MiB or did someone try something like 1.4MiB, which might require a TSR (like FDREAD) to be loaded for DOS to recognize it?
If you don't care for what's already on the floppies then why not try formatting one of them?

TM jumper is closed, all of them are in the default position as it is shown in the docs.

I did already tried to format, since I don't care of the content, but still got the "device not ready" or something similar.

Floppies were inside this case. But I can't guarantee that they were the original ones.

These are two of them. Left one I think has the handmade hole for flipping it in order to use the other side.

So first of all, these are 1-sided floppies. While most manufacturers made them all 2-sided by the time 5.25" drives got popular, and just branded as 1-sided, there is no guarantee they will work as such. Should though. And in any case these are double-density floppies and HD drives (such as your JU-475) can't write them very well. Sometimes it works, sometimes it doesn't, depends on the head and media (and contents). A HD drive should read a DD floppy though.

The extra hole would suggest these were used with something like C64 and flipped, if so you do need to reformat them. A PC FDC can't read GCR-encoded floppies. And if your drive can't properly write to DD media then these floppies will not be of much use as far as testing goes. But can still be used with 360k PC floppy drives.

To be sure if this drive works or not you need a HD floppy, and a known good one. So preferably not a NOS unformatted one. That being said, you mentioned a second floopy drive (3.5") that you have. Was it connected to the cable as well during testing? If not, connect it (make sure it has power connected as well) and try again.

Today I got for free IBM DOS 3.20 disks. Plus the others on the left, I guess some kind of software for connecting to a System/36.

None of them can be read. Same device not ready error. Current setup is A is a generic 3.5'' drive, B is the 5.25'' with DS2 jumper set. The 3.5'' drive is connected after the cable twist. In the BIOS the B drive is set as 1.2 MB 5.25'' drive.

Deunan wrote on 2022-04-08, 21:35:

So first of all, these are 1-sided floppies. While most manufacturers made them all 2-sided by the time 5.25" drives got popular, and just branded as 1-sided, there is no guarantee they will work as such. Should though. And in any case these are double-density floppies and HD drives (such as your JU-475) can't write them very well. Sometimes it works, sometimes it doesn't, depends on the head and media (and contents). A HD drive should read a DD floppy though.

The extra hole would suggest these were used with something like C64 and flipped, if so you do need to reformat them. A PC FDC can't read GCR-encoded floppies. And if your drive can't properly write to DD media then these floppies will not be of much use as far as testing goes. But can still be used with 360k PC floppy drives.

To be sure if this drive works or not you need a HD floppy, and a known good one. So preferably not a NOS unformatted one. That being said, you mentioned a second floopy drive (3.5") that you have. Was it connected to the cable as well during testing? If not, connect it (make sure it has power connected as well) and try again.

I don't understand how to recognise if the IBM floppies are 2-sided or not and also if they are double density.
The 3.5'' drive is connected.

As a rule of thumb if the floppy has an extra ring attached to the central hole, where the media is clamped to the spindle, it's a DD disk. Also that self-made write protect hole is a giveaway this particular floppy was used in 1-sided drive and flipped. So there is a good chance those are 1-sided floppies though yes, I can't be sure about that.

Does your drive attempt to spin the floppy at all when accessed? Does the motor turn on briefly when a floppy is inserted (or removed)? Does the head seek during BIOS drive detection phase (that might be disabled in the BIOS settings)?

Holy guacamole, it's working!

I just enabled floppy seek at boot, and now it can read the IBM DOS disks!

Formatted a C64 floppy as 360 kb one, first write was unsuccessful but tried again and it gone through. Read file back and was OK.

I'm very happy! Many thanks to all of you!

And now as next question... any ideas on how fill up the last remaing bays? 🤣

This is my "All-in-one" retro PC project!
Tualatin powered Abit VH6T motherboard with an ATI Rage 3D Pro, Voodoo 2 and a Creative AudioPCI (an okay-ish sound card I know, but I do have an ISA slot available so a future "retro-grade" may happen).