TE is for termination.
DS0-3 are the drive numbers.
So in an AT or XT machine TE would have a jumper if it's the last drive on the cable. Then you would just select your drive order by placing another jumper on DS0-3. AT and XT machines did not have a twist in the cable like newer machines so this was how you selected the drive order. I have the same drives in my commodore PC-10.

OK. I don't remember if my XT had a twisted cable but my drive seems to be configured for it. Anyway, I have left the jumpers untouched and I have tested the drive in my 486, in the edge position of a twisted cable. Its behaviour is the same as in those days. I took a disk that I could read, and even could copy its files to the hard disk, but when I tried to copy one file onto the disk it turned unaccessible and it could'nt be read any more.

I have found that the drive works well with high density disks but it does not with double density disks. I have tried 4 different 96 tpi MD2-HD disks and I can read, write and format (360 KB of course, because it is a 360 KB drive) all of them without an error. All the 48 tpi double density disks (whose data could be read perfectly) that I tried to write or format, ended up with a "track 0 bad" error and never worked again. Why?

One more problem. In windows 98, the first time you try to access the disk it shows a "drive not ready" error, but if you quickly click on the retry button it works. It is very important to click the button quickly, otherwise it throws the error again and again. This problem does not appear if windows starts in safe mode, where it works perfectly. Is there a way to fix this?

Contrary to what was stated earlier, the IBM PC and its clones (also including XT-class and AT-class) machines did indeed use a twisted FDD cable, exception of some unusual PC clones (such as the Tandy 1000) which relied upon the DS jumpers and didn't use a twisted cable.

FIXED UP! Now it can read, write and format Double Density disks perfectly. It can also read High Density disks but, as a result of the fix, it cannot write or format them. I am going to relate the repair process. May it help people repair their drives.

First I searched the Internet for the circuit board photo and compared to mine.

I found three differences in my board:

1) One added R33 resistor in parallel with the existing one in the other side of the board.
2) One added resistor in parallel with the last resistor in the RM1 resistor network (termination resistors).
3) An accidental tin solder drop over the R8 resistor which was shorting it.

Then I searched for the schematic but I could not find it. Instead, I found the schematic of the Chinon F-502II or F-502LII which seems to be quite similar for the most part to that of the FZ-502.

The two main ICs (Sony CX20185 and Toshiba TC8600F) are the same but there are some differences between this schematic and the FZ-502 circuit board:

- R33 in my board is R34 in this schematic.
- R15 in my board is R32 in this schematic.
- The terminal resistors (RM1 resistor network) are before the diodes, the other way around in this schematic.
- R11, R12, R13 and R14 in my board are the RM2 corresponding to DIR, STEP, WGATE and SIDE signals in this schematic.
- R7 in my board is R12 in this schematic.
- R9 in my board is R11 in this schematic.
- R8 in my board is R9 in this schematic.
- Maybe IC4 and IC5 are of the same model in this schematic but they are of different models in my board (different pin numbers).
- ...

There are more differences between the schematics and much more important than these without a doubt, but I did not want to deepen the subject (I had already found what I was looking for...).

The original R33 resistor in my board (R34 in this schematic) is 2,7 Kohm and the added one in parallel is 1,6 Kohm, so the resulting total resistance is 1 Kohm.
The resistor network includes seven 1 Kohm resistors but the last resistor in the network must be defective because the total resistance with the added resistor in parallel is 1 Kohm.
Maybe the drive did not pass the quality control and was repaired. I suppose that both resistors where added in the repair process and that the tin solder drop fell on R8 (R9 in this schematic) during this process. Then the write function of the drive was not properly verified. Because the one to blame is the shorted R8.

What I have learnt after my research on this malfunction is that DD disks and HD disks are made with different materials featuring different coercivity (300 oersted for 5.25" DD disks and 600 oersted for 5.25" HD disks) meaning that HD disks require a stronger magnetic field than DD disks to be written. The current passing through the heads of the drive generates the magnetic field so it is needed a higher current to write a HD disk than to write a DD disk.

R8 (R9 in this schematic) is the resistor which value determines the write current passing through the heads. With a short in R8 the current is too high to write a DD disk properly but it is fine to write a HD disk. After removing the short in R8, the current generated with the 3.3 Kohm resistor is fine to write a DD disk but it is insufficient to write a HD disk.

You cannot have it all.

By the way, I had not realized until now but there are more differences between both circuit boards. JP4, JP5 and JP8 differ from each other and in the first board there are green marks over the JP5 and JP8 places. I wonder why.

I have been wondering how HD drives face the problem of having to deal with both types of disks, so I have searched for the schematic of the Chinon FZ-506:

For DD disks it uses a 3.3 Kohm resistor (R50) and for HD disks it seems that a switch is turned on to connect in parallel the 3.3 Kohm and a 5.1 Kohm resistors (R50 and R49) resulting in a total resistance of 2 Kohm. I have thought that an intermediate value between 3.3 Kohm and 2 Kohm might do the trick so I have replaced my 3.3 Kohm resistor with a 2.5 Kohm one, and now my FZ-502 drive can perfectly read, write and format both DD and HD types of disks (both formatted to 360KB, of course).

Cannot do that.

1.22MB drive; you can only write and read only to 1.22MB disks.
360K drive; ditto only to write and read to 360K disks but only read by 1.22MB drive.

The differences are: track width of the 1.22MB is narrower by 50% than 360K head's track
And second difference is write amplification is stronger on 1.22MB as 1.22MB disks magnetic cohesion is harder to flip bits as opposed to since 360K diskettes has less magnetic strength required to change bits.

Third: all 5.25" drives does not have mode sensor that 1.44MB and 2.88 drives have.

Cheers,

pentiumspeed wrote on 2020-05-09, 14:24:

Cannot do that.

I am confused right now because I am not sure if you have not read all my posts or you have not undestood them.
I have done what I say that I have done in this thread, and not another thing. So, definitely, I can do it.

pentiumspeed wrote on 2020-05-09, 14:24:

1.22MB drive; you can only write and read only to 1.22MB disks.
360K drive; ditto only to write and read to 360K disks but only read by 1.22MB drive.

It will be difficult to understand each other if we refer to a disk using its physical type or its logical type in the wrong context. If we want to refer to the physical type we should speak of Double Density disks or High Density disks, and if we want to refer to the logical format we should speak of 360KB or 1.2MB (or many others, because you can format each physical type to various logical formats).

I am sure that HD drives can read and write DD disks formatted to 360KB (and they can also format them to 360KB). I do not know if HD drives can write or format HD disks to 360KB (I think they could do it if they were modified in the same way that I did with my drive). I also do not know if HD drives can write or format DD disks to 1.2MB (this looks more difficult to achieve).

pentiumspeed wrote on 2020-05-09, 14:24:

And second difference is write amplification is stronger on 1.22MB as 1.22MB disks magnetic cohesion is harder to flip bits as opposed to since 360K diskettes has less magnetic strength required to change bits.

I have already said that. I quote myself:

Bellator wrote on 2020-05-07, 21:51:

What I have learnt after my research on this malfunction is that DD disks and HD disks are made with different materials featuring different coercivity (300 oersted for 5.25" DD disks and 600 oersted for 5.25" HD disks) meaning that HD disks require a stronger magnetic field than DD disks to be written. The current passing through the heads of the drive generates the magnetic field so it is needed a higher current to write a HD disk than to write a DD disk.

pentiumspeed wrote on 2020-05-09, 14:24:

Third: all 5.25" drives does not have mode sensor that 1.44MB and 2.88 drives have.

I do not care. What I can say is that now, my Chinon FZ-502 DD drive can format HD disks (and DD disks) to 360KB and it can read and write them as long as they are formatted to 360KB.