Not my words.. I have a load of service notes in the old Amiga Repository on my G drive if you get stuck...
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1541 DIAGNOSTICS, Some symptoms and solutions for a sick disk drive.
DRIVE DEAD... OR NEARLY
Lets take it from the top. Does the drive initialize properly when first turned on?
The start up sequence should be: green power light on, red drive light comes on and goes
out while spindle motor turns for a few seconds and stops. If the power light (green LED)
doesn't come on, or is dim or flickers, you have a power supply problem... the 5 volt
line is bad. That usually results in a spindle motor that runs continuously and red LED
off. Check the bridge rectifier CR3 and the 5 volt regulator VR2. Note: if the regulated
12 volt supply fails, the motor will not run at all. If the drive activity light (red
LED) stays on and the motor runs continuously, it's usually an indication of a bad DOS
ROM UB4 (901229-xx). Anything that can cause the drive to fail to complete it's startup
sequence should be checked, such as UC4 (6502 MPU) and UC2 (6522 VIA). The smaller "glue"
logic chips are pretty rugged, but do sometime fail. Check UA1 (74LS14) and UD2 (7407)...
they have been known to cause those symptoms.
DRIVE INITIALIZES OK, BUT WILL NOT LOAD PROGRAMS
When the computer is turned on, the reset signal should cause the drive (and other
periferals like the printer) to reset: the drive red LED and spindle motor come on and go
off within a few seconds. If that doesn't happen, suspect the serial cable (try a
substitute) or the VIA chips in the computer or drive. If the computer resets other
periferals, it's probably OK. If the computer can't "see" the drive on the serial bus,
you will get an error message: "DEVICE NOT PRESENT" when you try to LOAD something. The
default (factory setting) for a 1541 is device #8. If your drive is hardware modified as
device 9 for example, and you try to read the directory (LOAD"$",8), you will get that
error message. If the VIA (UC3) 6522 interface chip in the drive is bad, the drive will
likewise be "invisible" to the computer. Check also UB1 (7406).
A "DRIVE NOT READY' message indicates that the computer can "see" the drive, but
there is no disk in it, or it's not formatted, or the drive door is not closed. A dirty
read/write head can do the same thing. The drive will respond by flashing the red
activity LED and banging the heads (looking for track zero). If the computer can access
the drive, but you can't load even the directory of a known good (formatted) disk, try
the INITIALIZE command, then try reading the disk again. To INITIALIZE the drive:
OPEN15,8,15
PRINT#15,"I"
CLOSE15
One quirk of the 1541 is the "drive lost" symptom: if the head, for some reason, gets
stuck past the directory track (18), INITIALIZE will return it to track zero and it
should then work normally. Note: turning the drive off and back on again will -not- reset
it if that's the problem! Some disk errors can do that to a drive and make it look
"dead". As an alternative, you could try formatting a disk... that will also return the
head to track zero. Lastly, if you insert the transit card (shipped with the drive) with
the drive turned off, it will push the head back to track zero. Inserting a disk is not
the same thing! The transit card has a tab on the front of it that does the job. With the
top cover off and metal shield removed, you can push it back with your finger (drive
turned off, of course) if you don't have a transit card.
If your computer setup or components have been moved recently, take note... drive
cables too close to the monitor can sometimes pick up interference from the flyback
tranformer in the monitor and garble the data. Move the drive and cables at least a foot
away from the monitor and try it again. If that helps, move the drive to the other side
of the monitor and keep the cables as far away as possible.
If you have re-initialized (or otherwise reset) the drive and it still doesn't work
(can't read a disk), it may be out of alignment. Try formatting a disk and see if it can
read the (empty) directory of that disk. If it can't, clean the head and try it again. If
it can, but can't read other disks, misalignment is a good possibility. Before you get
your tools out, there is one other thing you should check: see if the head assembly rails
are sticky, especially on a drive that has been unused for a time. With power off, the
head assembly should slide back and forth easily. If it seems sticky (experience helps),
the rails should be cleaned with strong solvent (acetone, MEK, paint thinner) and either
run dry or relubed with a tiny amount of graphite lube. Oil on the rails will work for a
time, but eventually picks up dirt and will get sticky again.
Drive misalignment is something that doesn't happen all at once. It is a gradual
process that begins with occasional errors while loading (red LED flashing), failure to
work with some programs, or excessive head banging (the drive getting "lost" and having
to go back to track zero to "find" it's place again.) Drives are forced out of alignment
(mostly while hot from use) by copy protected programs or disk errors that cause the head
to "bang" against the track zero stop repeatedly. If the alignment is far enough off,
you will get "FILE NOT FOUND" and red LED flashing... the drive tries and "gives up".
To properly realign a drive, you need special software. I use "1541/1571 Drive
Alignment" by Free Spirit Software. The flipside of the program disk is the alignment
disk, and as such, should not be copied (a copy is only as good as the drive that made
it). The program provides a menu screen that indicates what track you're on, drive speed,
etc. You make adjustments to the drive while watching the screen. The instructions even
tell you how to load the program when nothing else will load. You can -check- the
alignment of the drive without taking it apart, but realignment requires disassembly.
Drive speed can drift over time, but it's rather rare to find it off far enough to
cause problems. Spindle speed is reset with a small screwdriver adjustable control on a
PC board near the spindle motor on the underside of the drive. On older belt-driven
spindle motors, (synchronous motor... not adjustable) the belt may be slipping. On all
drives, the spindle or collar can get sticky and a tiny bit of lube helps. (Don't overdo
it... excess oil will be thrown off and could get on the disk). Make sure the latch
clamps the disk properly. Without a disk, move the lever down and see if the spring
presses the collar against the spindle to clamp it tightly. You can bend the tab down
-slightly- so it makes more firm contact. A slipping disk will produce random read and
write errors... -very- hard to track down. If you have any questions, email me at:
rrcc@u.washington.eduRay Carlsen
CARLSEN ELECTRONICS... a leader in trailing-edge technology.
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scuzz