The 3.5 is set to DS1 and the 5.25 is set to DS2 which is correct. The other jumpers are also correct for 3.5 = A and 5.25 = B. What type cable are you using ? You need to have a twist in it before the end and must use the end per the picture....if same as my Canon 7511 dual floppy drive.

Yes I have a twisted cable, with 5 connectors (MB connector + one double connector 34pin/34slots + twist + double connector 34pin/34slot)
The drive is attached at the end of the cable after the twist on the 34slot connector
I’m not sure if the jumpers under the white PCB (the ones directly on 5.25 drive) are at the right position? I was not able to find any documentation on them even on other TEAC standalone 5.25 drives, it seems to be a special jumper arrangement not found on other models 🙁

Not sure if it can help, but I booted a dos with 3.5 drive, and when I try to format a 5.25 floppy, the format starts for a 1.2M floppy, and at about 34% the drive is doing a noise like it find bad sectors until the end of the format process. At the end, I have an error “can’t write boot sector” and the new formatted floppy still not accessible.
I did the same with a 360k floppy, I had to force the format to 360k because it is detected as 1.2M but the result is the same…

jnjn63 wrote on 2022-02-21, 09:50:

when I try to format a 5.25 floppy, the format starts for a 1.2M floppy, and at about 34% the drive is doing a noise like it find bad sectors until the end of the format process

If that drive is indeed a 1.2M and not 360k one, it's double-stepping. Thus you are running out ouf head movement after about 42 steps, which is that 34% you get. I would not be doing that too much, you risk damage to the drive.
It's very rare (and I mean very) to have a 5.25" drive that can be internally configured to double-step. That is usually what the FDC does. So what you have there is simply a double density 40-track drive, a 360k one in other words.

I’m surprised because TEAC FD-505 is described as a 1.2Mo drive ?

Hm, according to the info I can find the 5.25" part is supposed to be functionally identical to FD-55GF drive. I have some experience with the newer FD-55GFR model, but not the original GF.
There is a signal on pin 2 of the ribbon cable that tells the 5.25" drive to use either high or normal density mode. That signal is apparently ignored by the 3.5" part (so no 3-mode operation). But even if that was wrong it should not result in double-stepping because 80 tracks in normal density is a valid format. Not for PCs but it is used on other computer systems (Atari ST?).

This is a combo unit but apart from the PCB that multiplexes the signals, each of the drives should have it's own electronics and a set of jumpers. Some (most/all) of these might be permanently soldered with a wire though. Can you please make some decent photos of the 5.25 PCB?

Here are additional photos

It’s very strange I tried with an isa fdc and I was able to format a 1.2mb floppy, but all my floppies (360 or 1.2) was not readable on it and 360k floppy was not formattable. Then I used back the integrated fdc and the 1.2mb floppy were unreadable so I formatted it a new time successfully and I was able to make it bootable.
I booted up on it few times, then I tried another floppies (1.2 and 360k) and now i can’t read any floppy, even the bootable one..
The led of the drive don’t power on anymore (even during drive seek) and when I try to format a floppy I get a track 0 error….

I need a floppy drive expert :p

Here's mine. Looks completely different though.

jnjn63 wrote on 2022-02-21, 17:40:

The led of the drive don’t power on anymore (even during drive seek) and when I try to format a floppy I get a track 0 error….

AFAIK these combo drives were not exactly known for their reliability. This is due to their smaller size I guess because full-size TEAC drives are tanks, not much goes wrong with those even after years of use.
You have some failed electronics I think - could be as simple as dirt, might be as bad as corrosion of the PCB. Frankly at this point the drive needs proper servicing, and by that I mean more than just blowing some air throug it...

OP what is the revision of your unit?

I have seen these in the wild. There are probably more:

• FD-505-000-U
• FD-505-100-U
• FD-505-200-U
• FD-505-202-U5
• FD-505-222-U5
• FD-505-300-U
• FD-505-300-U5
• FD-505-318-U5 (thanks wiretap)

ETA: This is from my notes:

The FD-505 drive family consists of two slim-line drives in a single 5.25" form factor. They were produced in four major revisions, each with several sub-variants:

• FD-505-000 - require the large Molex type power connector (5/12V); have two blocks of jumpers on the 5.25" drive; third block of jumpers on the left side of the 34-pin connector are not to be changed
• FD-505-100/200/300 - have one block of jumpers; need the small Berg power connector

ETA2: here is manual for the FD-505-000: https://gekk.info/misc/Teac%20FD505%20Dual%20 … %20Diskette.pdf

I will check the version soon. For the third block of jumpers next to the 34pin connector I think I’ve lost the initial set up..

They're correctly set. Don't touch anything there. According to the manual (p. 4) your drive is configured for Drive A: 5.25" and Drive B: 3.5" which is the factory configuration.

According to the manual (p. 5) your drive is configured for Drive A: 3.5" and Drive B: 5.25"

Hello
References are:

Fd-505-000-U for combo made with a Fd-155gf-007-u 5.25 drive.

After few times of clean, drive seems to work better, I can now format both 1.2M and 360k disks. All my existing floppies seems to be unreadable (but I didn’t used them since 20years) so maybe it’s normal ?
It seems format tool detect DD floppies as 1.2M, I have to force 360k maybe it’s normal too?

After a clean format DD and HD floppies works and can be bootable.

I still have a drive 40 error at first boot but this error disappears when I restart with ctr alt supr

I have one of those and it's never given me any trouble, however given how expensive these things are nowadays I don't like using it.

I also have a -222-U5 and a -300-U, however the last one has a broken 3.5" drive, so I disconnected the ribbon cable to the smaller drive and it now functions as a simple 5.25" drive.

The 3.5" drive is not labelled on these units, however I believe all of these models use a version of the FD-05HF.

jnjn63 wrote on 2022-02-22, 07:18:

All my existing floppies seems to be unreadable (but I didn’t used them since 20years) so maybe it’s normal ?

I had this problem with the -300U and it disappeared after I moved the drive to a different (older) computer. The disks were (mostly) OK but there was some weird incompatibility between the drive and the motherboard I was originally using.

It's always helpful to have multiple drives and retro computers to troubleshoot issues like this, but given the cost of the hobby nowadays I'm aware that's not helpful advice.

jnjn63 wrote on 2022-02-22, 07:18:

It seems format tool detect DD floppies as 1.2M, I have to force 360k maybe it’s normal too?

I don't remember but this may depend on the DOS version you are using.

Beware that Windows XP dropped support for DD 5.25" drives but still supports HD 5.25" drives. I'm not sure if it supports formatting DD floppies in HD drives. I have a dual boot Windows XP/ME machine with a DD 5.25" drive and it's only accessible in Windows ME. Windows XP sees it, but gives an I/O device error when I try to use it.

Have the same model as the OP (FD-505 000-U / FD-155GF 007-U), tho in my case its the 3.5" drive that failed 🙁

For reference my replacement part would be FD-05HF 030-U / PN: 19307520-30, if you could get them - these are OEM only so were never on general sale (used in TDS520A oscilloscope from Tektronix & some medical scanning systems)

That's useful to know, thanks.