Amiga Technical Resource


Fitting a PC floppy drive to the Amiga



Introduction:

The floppy disk drive in older Amiga computers are starting to wear out, particularly in machines which have had many years of constant disk swapping.
For those that can't get a real Amiga drive, you can use some types of PC floppy drive. Some drive types are more suited to the job than others and the older Panasonic JU257 models seem to work well.
The limitations are that even though it might be a high density PC drive, you will only be able to use it as double density (880kb) on the Amiga. High density mode on the Amiga is a bit more complicated and requires a special drive.
For more information, there is a drive compatibility list available here.

It is worth pointing out that quite a number of late model PC drives will not work correctly with the Amiga no matter how you modify it. Alternatively you might want to buy a drive controller such as the Catweasel from Individual Computers which allows many options for reading/writing disks of many formats on multiple platforms.

Other solutions exist. Buy a replacement floppy drive from Amigakit.com or look at purchasing a floppy drive adaptor PCB from Ian Steadman. These are both available ready-made and as a kitset.

Older drives including some Sony and Chinon models will often work by simply swapping the diskchange and ready line (pins 2 and 34) in the ribbon cable.



Converting a Panasonic JU257 floppy drive

These modifications to the Panasonic JU257 means it will plug into any Amiga as a direct replacement for the unit 0 (DF0:) internal floppy drive. I have had reports that newer versions of the JU257 are different from the older ones in that the labelled pads are not there, so be warned!




Read me first

The JU257 drive seems to be difficult to find these days, so refer to the notes above for other solutions.

The information provided below outlines the modifications which will work for some models of JU257 and serves as a rough guide only. Note that this is not intended as a step-by-step guide, these details are a copy-and-paste of an Email I wrote over 12 years ago detailing a conversion I'd performed. Various individuals have requested that I publish the information, which you can find below. Just don't expect to find a floppy drive that you'll be successful with!

In addition, Ian Steadman has some useful notes and utilities for floppy drives here which may assist users in their own modifications.


Some of the things you'll need:

- Panasonic JU257 PC floppy drive
- small sharp knife, such as a craft or Stanley knife.
- small electronics type soldering iron and very fine solder.
- a good soldering ability
- about 2 inches of small, insulated hook up wire (about 0.5mm diameter or less). Or better, enamel "wire wrapping" wire
- a #0 Philips screwdriver
- needle-nose pliers


Please note that you'll need some very good soldering skills, so if you aren't used to soldering, give these instructions to someone who does.


First take the cover off the bottom of the drive to expose the under side of the PCB.
You need to unscrew and lift the PCB up to work on it.

There are two flexible looms running to the heads which can be carefully unplugged using the needle-nose pliers. You might want to mark them so you don't swap them when reconnecting later.
The stepper motor which moves the heads is connected to the PCB with a loom that's permanently soldered into the component side of the board. It's a bit tricky to get it off without damaging anything, so you can try to work on the board with the motor still attached if you like.
I decided to de-solder the loom at the stepper motor, but you have to be extremely careful as the metal pins in the motor are bedded in plastic which melts very easily, causing pins to come out.

Once you have access to the component side of the PCB, you'll need to locate some pads/jumpers.
Not far back from the 34 way connector you'll find 3 pads with the labels RY and DC beside the outer two. If you look VERY carefully, you'll see that the centre pad is linked to the DC side pad.

Note that if you can't find these pads, it might be a later version of the drive which doesn't have them. If so, get another drive, or you're on your own from here!

Using the knife, cut the PCB track running from the centre pad to the DC pad.
Once that is cut, use the knife to scratch the green coating off the surface of the RY, DC pads and centre pad between them.

Next get your soldering iron and link the centre pad to the RY pad. You might be able to "blob" solder between them, but it might be better to use a fine bit of wire. A pair of tweezers might help here.

Now get the hook-up wire. It has to join the DC pad to pin 2 on the 34 way connector. Pin 1 is nearest the outside edge of the drive and connects to ground, as do all the other odd numbered pins. Pin 2 is the one beside it......hopefully you can work out the correct pin, sometimes the end ones are labelled.

One final link to make. Locate the drive select pads. They look similar to the RY/DC ones but will be labelled something like DS0 and DS1.
You'll notice the DS1 pad is linked to the centre pad. Cut this link with the knife..
Scratch the green coating from the centre and the DS0 pad then solder link the two together.


Now you can reassemble the drive and try it. Reconnect the stepper motor and plug in the heads into the correct sockets. Screw the PCB back on and connect the drive to the computer.
If being installed into an A500/600/1200, you can remove the drive's front bezel which is just clipped on.
Make sure the 34 way cable is wired "straight" and doesn't have a twist in wires 10 to 16 (like PC drive cables are).

Once the computer has passed the power up tests, it should begin polling the drive about once every two seconds, you'll hear this as a continuous pulsing or clicking noise. Insert a disk and make sure you can read/write to it.

If it doesn't work, re-check your soldering. Make sure that when you cut the linked pads, that the track is actually open circuit. You can use a multimeter to check.
Also check to make sure there is +5V and +12V at the drive. Red wire= 5V, yellow=12V.
If the drive LED is on all the time, the 34 way connector is probably upside down. Power off and turn one end over. If there is a coloured stripe on one side of the ribbon cable, it usually indicates pin 1.


You can browse some files and pictures of other conversion notes via FTP by clicking here.
Feel free to contact me with any questions or problems.


Have fun!
Anthony.







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