The magazine of the Melbourne PC User Group 3.5 inch Drive XT Installation Tom Coleman

I decided that rather than purchase a new controller card I would remove one of the 5.25 inch drives. The controller I have will only support two floppies. 

I was quoted from $150 to $200 for a 3.5 inch disk drive without a cable. I finished up paying $175 for a Panasonic drive with a 5.25 inch half height chassis to fit in the drive bay. 

There is a problem with the cable as the 3.5 inch drive uses a 34 pin plug fitting but the 5.25 inch drive uses a 34 pin edge connector. As a result I could not use the old drive cable and had to make up a new one. I had to purchase two 34 pin edge connectors and a 34 pin plug, plus 40 cm of 34 wire ribbon cable to make up the new cable. I received a few cents change out of $10 for my purchase. They are available from most of the electronics supply shops. Radio Parts, Rod Irving, All Electronic Components. All in the city of Melbourne. 

Theoretically you only have to open the fitting, place the cable in the back and squeeze it onto the cable with a vice. I broke two fittings opening then. You have to move them GENTLY and EVENLY otherwise the sides break off. I then put one fitting on the wrong side of the cable. It pays to think it through before rushing in. If you can find an experienced person to guide you through the first time it will flatten your learning curve no end. 

You need to be aware of a few rules regarding floppy disk drives and cabling. 

Cables can be straight through or twisted. In either case drive A: goes at the end of the cable and drive B: goes in the middle. Only two drives per cable. 

Whilst the electricity does not care what colour the insulation is, it is conventional to have the edge of the cable with the coloured wire (usually red) going to the number one pin on the plug. The number of the pins is usually marked on the circuit board. 

There are jumpers or switches to be set to indicate when a drive is drive A: or drive B:. If you have a twisted cable then both drives are set to drive B:. 

The drives are numbered as starting either 0 or 1 which would be drive A: and the next number would be for drive B: and so on. Drive A: (the one at the end of the cable) needs to have a Terminating Resistor in place. Drive B: must have it removed. This can be either a jumper or a thing that resembles a chip but is usually a different colour. Blue is common. Its position is usually marked on the circuit board. 

The newer disk drives may not use a terminating resistor. However jumper/switches must still be set for the drive number. 

Apart from the Terminating Resistor and the drive number options you need to choose a jumper/switch to indicate the status of pin 34. You have two options Ready Signal (RY) or Disk Change (DC) Signal. So far as we are concerned Ready signal is never right. Only set it for Disk Change.

Then you can choose between PS2 polarity, which is auto sense, or AT polarity. I chose AT to go with my XT. 

Finally you must choose when the spindle motor is turned on, either with the motor on signal (MO) or the drive select signal (MS). 

This was the only manufacturers default setting that I had to change. It was set to Motor On (MO). I assumed that the manufacturer knew best and spent a day scratching my head wondering why I was getting no response from the drive. Changing to (MS) fixed it up. 

Whilst all this was going on I took the precaution of checking the wiring of the power adapter supplied with the drive. The fitting on the Panasonic drive is smaller than the standard fitting and they give you an adapter. 

There are four wires. The outside wires carry 12 volts on one side and 5 volts on the other. If you get it wrong you zap the 5 volt circuit board with the 12 volts meant for the drive motor. 

It pays to check. 

Having set all the switches/Jumpers and finally got the cable made up I mounted the drive in the chassis. This is a frame made to hold the disk drive and fits into a 5.25 inch drive slot. 

Didn't have much trouble with this but as the 3.5 inch drive is much smaller it becomes inaccessible if it is mounted below the 5.25 inch drive. I intended to use a 5.25 inch drive as A: so it finished up in the bottom of the bay which is not the conventional place for drive A:. This should not be a problem for those with drives side by side. Having assembled the whole thing into the computer I now needed to tell the computer it was there. I modified the CONFIG.SYS file with the line
      DEVICE=DRIVER.SYS /d:1 

When I rebooted I first thought that I had done something wrong but after ringing around suppliers and knowledgeable users I was sure that I had done everything right. 

I could access drive B: but it would only format the drive to 360K. When I tried to FORMAT B: / T:80 I got the error message "Parameters not supported" 

After much fiddling about I tried accessing drive E: and sure enough there was my 3.5 inch 720 kB floppy. Accessed as drive B: it thought it was a 360 kB drive but it was a 720 kB drive as drive E: 

I ASSIGNed B: to A: and there we were. 

I have a sneaky suspicion that there has got to be an easier way. I believe that there is a command that can be put into the CONFIG.SYS which reads DRIVPARM=/D:1. This is supposed to be a better way than using Driver.sys. I haven't tried it yet and won't have the opportunity to do so before the deadline for this article expires. 

Reprinted from the June 1990 issue of PC Update, the magazine of Melbourne PC User Group, Australia

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