Getting FDS disk games to boot that normally don't
Brad Taylor

During the research & development stage I went through for finishing the FDS 
loader project, I discovered a way to get FDS games that normally don't work 
to now boot up successfully. The trick to doing this lies in a part on the 
disk drive mechanism itself.

When you insert a disk into the drive, the disk bay lowers down, and 
eventually the bottom side of the magnetic floppy contacts the head (the 
head is at a constant alditude). On the top side of the magnetic floppy, 
some kind of arm with a brush on it lowers onto the floppy's surface, and 
applies pressure on the floppy against the head, to allow for closer (or 
better) contact with it.

I have discovered that by applying some extra force on this brush arm, disk 
games that regularly do not boot up, will now work. However, do not apply 
too much force, otherwise the friction from the brush will slow down the 
disk's RPM, and the RAM adaptor will not be able to boot from it anyway, 
since the transfer rate will be out of range.

The permanent fix to this is to increase the tension that the spring already 
in there applies. To remove the spring, you must pop out that pin that it's 
wrapped around (which is also the pin that supports the arm as well). With 
the front of the drive facing towards you, chissel the pin from the right 
side of it to pop it out.

It is neccessary to re-torque the spring, since simply adding an extra 
revolution to the windings will offer too much tension. Use both your hands 
(you may need to use needle-nosed plyers) to twist the spring in the SAME 
direction in that it is supposed to be applying pressure in. This will 
increase the size of the radius of the spring's coil. Don't overdue the 
re-torquing; hand strength is all you need to do it. After this, the spring 
is ready to be put back into the drive. It will be a little tricky to put 
the spring back onto the pin (with the arm kind of in the way), so this 
requires patience. If putting it back in seems easy, this means that you're 
not adding enough revolutions to the windings of the spring for force. At 
any rate, make sure that the force applied after you put the spring back in 
is a good deal more than when you removed it.

For an easier way of incerasing the pressure the brush arm applies against 
the floppy without having to adjust/replace the arm's spring, I'd try taping 
some weight onto the arm (for example, a few pennies or dimes would make up 
the weight well). Personally, I tried this before re-torquing the spring, 
and it didn't work out very well (mostly because the tape was always 
brushing against somthing).

As for why certain games work with the default pressure, while others 
require more, I would speculate that the surface of the disks in question 
are rippled, possibly left that way after years of use. Without enough 
pressure, the ripples are the only thing the head makes contact with, which 
is only a fraction of the area it needs to contact in order to read the 
magnetic data reliably.

But don't take my word for it- just take a look at the surfaces of FDS disks 
that boot, and compare it to ones that don't. You'll find that working disks 
have a uniform surface, while the others will have tracks of wear on them, 
with most of the wear appearing at the end of the disk (the most inner 
tracks). The wear appears at the end because this is where the disk head is 
put to rest after every disk scan.

EOF