Connecting an FDD for PC/AT compatible computer to PC-9821
( Implementation )

• Introduction
• Application to other models
• Common precautions
• List of FDD modified drawings
• Reference

• In an FDD with a 34-pin interface, with some exceptions, the 360/300 signal input to pin 2 of the FDD must be inverted using a 74HC14 or the like.

• In general 3.5-inch FDD, there are FDD that does not require inversion of 360/300 signal and FDD that requires it, so in consideration of the uniformity of the appearance of the drawing, the matters related to 74HC14 are described in the special notes. On the other hand, the thin FDD basically needs to invert the 360/300 signal, so 74HC14 is shown in the drawing.

• When connecting a PC-9821Xa7 or later desktop machine and FDD with a flat cable, modifications related to so-called "reversible cables" and "reversible connectors" must also be made. Specifically, it is necessary to replace the flat cable with one whose terminals are crimped in the same direction, or to insert a conversion board between the existing flat cable and the modified FDD to absorb the difference in terminal direction.

• There are two types of Ready signals: one is to use a regular Ready signal and the other is to substitute a pseudo Ready signal. In the case of using a pseudo-Ready signal, there is a possibility of causing some problems if the wiring is simply connected. Please refer to "Consideration and Verification of MSX FDD READY Signal" by HP on PS2Linux DASH for the countermeasure.

• In the drawing, the Disk Change signal is shown to be output to pin 33. However, as described in the overview section, this is not actually used, so the modification is omitted in the FDD shown in the reference photo.

For this FDD, it is necessary to modify the jumper. For details of jumpers, refer to the separate drawing ( Jumper Setting Table ( Y-E DATA YD-702D-6639D ) ) .
Reference photo ( Before renovation,After renovation )

In order to modify this FDD, it is necessary to remove and reattach the FPC and FFC cables for the stepping motor of the head in addition to the control board at the same time.

Once the control board is removed, it is necessary to adjust the position of various sensors in micrometer steps. Therefore, although reference drawings of this FDD are provided, we recommend avoiding modifications as much as possible.

In the case of switching only between Disk Change and Ready signals, there is a method of modification without removing the control board. Specifically, after moving the head to the innermost side, "R45" and "R46" related to switching are modified through the gap between the head and frame inside the FDD. With this method, misalignment of various sensors can be prevented.

For this FDD, it is necessary to modify the jumper. For details of jumpers, refer to the separate drawing ( Jumper Setting Table ( TEAC 3-row type ) ) .
Reference photo ( Before renovation,After renovation )

• *1
  The string in round brackets indicates the model number of the control IC, and the string in square brackets indicates the number of the pin outputting the Ready or pseudo Ready signal of the control IC.
• *2
  The format type of the disk is 2HD.
• *3
  The format type of the disk is 2HD.
• *4
  If the access lamp does not light, shorting the HDR jumper will light the FDD access lamp.
• *5
  The information "pin 26 and pin 42 of FDN30x are connected" in the drawing was provided by Crusher-K.
• *6
  FD1231H can also be used with similar modifications.
• *7
  When inputting a 360/300 signal to the Density pin, the signal should be inverted using 74HC14 or similar. (The inverting circuit may not be shown in the reference photo. )
• *8
  It seems that YD-702D-6238D can be used with similar modifications.
• *9
  It seems that MPF920-F and MPF920-L can be used with similar modifications.
• *10
  The D359M3D may also be usable with similar modifications. However, since the pattern of the control board is different, it is necessary to carefully examine the signal extraction location based on the reference photo.
• *11
  JU-257A607PC can also be used with similar modifications. However, additional work to short the "R71" is required. Also, it seems that JU-256A347P can be used with similar modifications.
• *12
  It seems that FD-235HG-B380-U can be used with similar modifications.
• *13
  It seems that FD-235HG-C122-U5 and FD-235HG-C635-U can be used with similar modifications.
• *14
  It seems that FD-05HG-8745-U can be used with similar modifications.
• *15
  2DD can also be read/write, though unstable (not sure if it can be formatted) .
• *16
  2DD is also readable and writable (not sure if it can be formatted) .
• *17
  The JU-256A048PC may also be usable with similar modifications. However, since the pattern of the control board is different, it is necessary to carefully examine the signal extraction location based on the reference photo.
• *18
  The specific cause is unknown, but we have confirmed that there are some units that do not work properly even after modification for some reason.
• *19
  It seems that FD-235HF-7291-U5 can also be used with similar modifications.
• *20
  It seems that MF355H-348MN can be used with similar modifications. However, the modification to invert and input the 360/300 signal by cutting pin 13 while the control board is fixed to the FDD housing requires removal and reinstallation of the 26-pin terminal installed on the control board, making the modification highly difficult. Therefore, it is better to prepare a conversion board separately from the FDD.