Famicom Disk System

What You’ll Need

• Famicom Disk System
• Replacement Drive Belt
• Phillips Head Screwdriver
• 1.5mm Hex Head Wrench (needed for Spindle Hub Adjustment)
• Needle-nose Pliers (needed for Spindle Hub Adjustment)
• Micrometer Calipers (needed for Magnetic Head Adjustment)
• X-Acto Knife or needle (needed for Magnetic Head Adjustment)

Step 1

Turn over the FDS and remove the six (6) phillips head screws that hold the casing together.

Step 2

Turn the FDS over and remove the top cover. At the back of the FDS there is a rectangular battery tray which is fastened with two screws. Remove the screws and the tray. Using your thumb and index finger, slowly move the connector in the back of the disk drive from side to side to loosen and unplug it. If you are having trouble removing the cable from the connector, remove the four screws holding the drive to the base of the case and move the drive forward for additional working space.

Step 3

If you haven’t already, remove the four screws holding the disk drive to the base in the step 2. Lift and remove the front trim piece. Once the drive is removed from the casing, look for the two wires which are circled in blue in the picture below. Each wire has a piece of the metal casing holding it in place. Bend the metal clips back and carefully release the wire. This is very important to perform since the wires could end up breaking off.

Step 4

Turn the disk drive over and remove the three screws shown in the picture below, ignoring the top left one at this time.

Step 5

Once the base removed, the drive belt is visible. In this case it hasn’t broken, but it has stretched so it will still need replaced. Remove the four screws shown in the picture below and carefully lift the circuit board. Underneath the circuit board is where the gray wire is connected with a four pin connector. This can either be left alone or you can disconnect it, but the drive belt can be replaced with it still connected.

Step 6

Remove the three screws shown below and then turn the metal triangle clockwise and carefully lift it out under the circuit board. Be careful not to lose the circular plastic shims that are between the triangle and gears.

Step 7

Once the metal triangle is out the way, it’s time to attach the new drive belt. Because the belt goes between one of the legs on the metal triangle (the one with two screw holes) you cannot attach the belt and then the triangle, you have to connect both at the same time. First place the drive belt under the correct leg and place the triangle back in the top right corner and slowly turn it.

Carefully move the belt so it goes around the white circular drive cog. Once the belt is around the bottom half of the cog, carefully stretch it to the top left-hand corner around the motor. Check that the drive belt is lined up and then slot the triangle back into place. It should click as it goes into position.

Step 8

Now that the belt is in place, the circuit board needs to be replaced. Note that the underside of the circuit board has small black switches that must be aligned in their respective slots. To correctly place the board, it is sometimes necessary to slide the pressure arm assembly back until the board can be correctly seated.

Step 9

Replace all the screws in the circuit board and those that hold the drive to the disk case. Replace the wires under the metal tabs and press the tabs into place to secure the wires.

Since it’s easily accessible with the case removed, clean the magnetic head using a cotton swab and some isopropyl rubbing alcohol before testing the drive.

Test the drive by attempting to read a known good disk. If it correctly reads the disk, replace the trim ring and disk case. You’ve now successfully replaced the drive belt. If it doesn’t work, see Troubleshooting below.

Troubleshooting

If your drive isn’t correctly reading disks and is instead throwing error codes, you may need to adjust the drive speed, correct alignment issues, adjust the spindle hub, and/or adjust the magnetic head alignment. It’s also a good idea to check the cotton/felt pad (small, circular cotton/felt part that touches the disk surface) on the pressure arm to ensure it isn’t too worn or thin, as this can cause error 27 to be given when attempting to read a disk. It should be replaced if necessary.

Drive Speed Adjustment

To adjust the drive speed, use a small flat head screwdriver and adjust the variable potentiometer on the top of the motor in small increments and re-test after each adjustment. The drive speed adjustment can also be calibrated using Copy Master.

Alignment Issues

If the read head on the FDS isn’t correctly moving, is getting stuck, or is making clicking sounds, you probably haven’t correctly seated the circuit board, switches, or gear mechanism. Remove the drive and have a look at these items. The gear mechanism should click into place when it’s correctly seated. You may need to slide the pressure arm forward to get it to correctly seat. Correct any alignment issues with the remaining items, put the drive back together, and re-test.

Spindle Hub Alignment

This is perhaps the most important and misunderstood adjustment when replacing a FDS belt. Photo Source

Why it’s important: On the top of the metal hub/spindle is a pin with a spring that allows it to move up and down. This pin fits into the small hole in the disk center and turns the disk. It also positions the disk media in relation to the magnetic head. The positioning of this metal hub is vital since it determines when the magnetic head starts to read data from the disk. A few degrees off, and the disk system will throw error codes, most typically 22 and 27.

One way to adjust the spindle hub and ensure it is correctly positioned involves removing the top portion of the disk drive after the belt has been replaced. To do this, first remove the 3 springs attached to the side of the disk card holder with needle-nose pliers.

Push the white lever as indicated for the disk card holder to descend.

Next, push in the eject lever to raise the disk card holder while lifting the pressure arm out of the way.

Lift the top of the disk card holder off the drive. Now you can see the read head and spindle hub.

Check the small hole by the spindle as pictured. If you see white gears through the hole, turn the drive mechanism by rotating the gears on the bottom side of the drive.

You should see the spindle assembly moving toward the front of the drive and then hear an audible “click” as it stops in the read-out position. There should be a metal plate between the spindle hub and magnetic head. Loosen the 1.5mm hex head set screw in the spindle hub and position it as pictured. It’s important to maintain the correct vertical alignment of the spindle hub, too, so make a note of it before first loosening the set screw. This is the factory positioning of the spindle hub. The set screw may or may not align with the indentation on the spindle, but it’s not important that it does, since variations in how the gears were replaced when replacing the belt can potentially move it out of position. Tighten the set screw once it is in position.

Once aligned, reattach the disk card holder with the springs, the front plate, the bottom plate, and reconnect the pin connector on the back of the drive. Test it with a known good disk.

If it still doesn’t read disks correctly, you may need to adjust the spindle hub position again. You can do this simply by removing the front plate, loosening the set screw, and rotating the hub a few degrees and tightening the set screw. Test after each adjustment. If the drive that your disks were written with had the spindle hub position out of factory alignment, you will have to adjust your drive’s spindle hub until the disks can be read. This is potentially a problem with any rewritten disks that aren’t official Nintendo disks from the factory or Disk Writer kiosks.

This adjustment should allow you to successfully calibrate your drive to read FDS disks, although it will probably take some time to get it correctly positioned.

Magnetic Head Tuning Method

Article by Rob Budrick

A method to consider if you’re unable to get your FDS to correctly read disks involves adjusting the magnetic head via the adjustment screw. I would caution you to carefully read and understand this before attempting it on your own drive, since the alignment procedure could potentially take a long time if the measurements noted in this section do not work for your particular drive. If you do attempt this method, please send your feedback to me via the Contact Form.

To adjust the alignment of the magnetic head via the adjustment screw, you’ll need a Phillips head screwdriver, an X-Acto knife or needle, and a precision micrometer caliper.

In the FDS at the back of the drive tray you will see the following adjustment screw:

The screw adjusts the forward and backward positioning of the metal plate upon which resides the magnetic head. Having the magnetic head in the perfect position is crucial to having it optimally read disks. Also, the quality level of disk media varies greatly, with licensed Nintendo brand disks being the highest, and copied, third party, and bootleg disks being the lowest.

You will probably notice some colored (usually pink-colored) glue all around the screw, which was probably applied at the factory to keep it in the correct position. Over time, all FDS drives will probably require realignment. To adjust the screw, the hard, brittle glue must first be carefully removed from all around the screw, including the underside. The glue can be removed using an X-Acto knife and/or a needle.

In the photos below, you will see the drive head on the right and the adjustment screw on the left side. On the far left is the head of the adjustment screw, as noted in the photo. Note that there is a spring that goes over the screw and sits between two metal outcroppings. You will be using the caliper to measure between these two outcroppings.

As the adjustment screw is turned, the distance between the outcropping will change, since they sit on separate metal plates. Turning the adjustment screw clockwise decreases the distance between the two plates and turning it counterclockwise increases the distance. One quarter of a turn is approximately equal to .1mm, give or take 2 to 5 hundredths of a millimeter. Generally, you should only make small adjustments before measuring.

The red arrows show the distance between the plates and are the desired places to position the calipers to take the measurements. Make sure to not place the caliper over the adjustment screw, but just to the left or right of it, as the arrows suggest.

You may find that the caliper gives varying readings. To ensure the best possible measurements, it’s important to use a new battery in the caliper. Also, these are precision instruments, so adjustments can be a couple hundredths of a millimeter different each time if the method you use to take the measurements varies. Remember that if the calipers aren’t angled perfectly over the object being measured, they will give a higher reading because the tilt widens the gap on the calipers. When taking the measurements, you should use little pressure but make sure the caliper is completely closed. Take each measurement 5 times to ensure you are being consistent.

The optimum outside distance between the two metal outcroppings should be 10.68 to 10.72mm (0.421 to 0.426 inches). There is a variance in which the FDS will read disks outside of the noted range, but 10.68 to 10.72mm are the optimum measurements. If you have disks that don’t work at 10.68, adjust it up slowly and re-try at every small increment you can up to 10.72mm. I’ve found that few disks work after 10.72mm (except in rare instances), so I wouldn’t recommend going beyond that adjustment. If the disk doesn’t work in this range, it may be damaged or need to be rewritten.

The absolute lowest range I’ve found that disks will work within is between 10.57-10.59mm. These disks were never used, Nintendo-brand disks. Adjusting lower than this range and using the program FDSLoader as a tool, I saw the amount of blocks FDSLoader could read start to drop off, or rather, it would count the correct number of blocks but read the data within them incorrectly (re: corrupt data). The absolute lowest point at which you will likely see FDSLoader count the number of blocks correctly, even if they are all corrupt, is somewhere between 10.52-10.53mm. After this minimum range, it counts the amount of blocks incorrectly. Note that in extremely rare cases, you may even be able to read a disk in excellent shape from 10.49 up to 10.79mm, although it is unlikely based on my experiences.

If you attempt this adjustment, please remember to leave feedback through the Contact Form.

Thanks to SimplyNES for permission to use parts of their tutorial and to Rob Budrick for the magnetic head adjustment article.