1541 DIAGNOSTICS 2-15-08.

           1541 DIAGNOSTICS
	    Some symptoms and solutions for a sick disk drive. 
                 latest updates or corrections: 2-15-08

     To properly diagnose a potential problem, you have to know exactly how 
the drive should respond when it's working correctly...
 DRIVE POWER UP: Green power LED comes on and stays on, red activity LED comes 
on and spindle (which turns the disk) motor runs for about two seconds, then 
red LED goes out and spindle motor stops. There is no stepper (which moves the 
head assembly) motor activity at this time.
 COMPUTER POWER UP (OR RESET): Drive red LED should come on and spindle motor 
should start, then LED goes off and motor stops within two seconds.
 READ DIRECTORY: Insert a known good disk and type: LOAD"$",8 and hit the 
RETURN key. The disk should spin and the stepper should move the head to track 
18 and read the directory. The screen will show: SEARCHING FOR $. If it finds 
it, the screen will display READY. Then you can type LIST to see the contents 
of the disk. Note: some program disks will not have a directory you can list. 
If the disk read fails for any reason (drive door open, unformatted disk, bad 
chips in the drive, etc.), the drive red LED will flash and an error message: 
FILE NOT FOUND will appear. If you read the disk error channel, it will 
display: 74, DRIVE NOT READY,00, 00.
 INITIALIZE: This command from the computer should move the head from wherever 
it was to track 18 (directory) and the disk should spin. The head will not move 
(but the spindle motor will turn) if it is already over track 18. If there is 
no disk in the drive, or you insert an unformatted disk, or if the drive door 
is open, INITIALIZE should cause the spindle motor to run and the head to seek 
track 18 (directory) anyway. When it tries and fails, it will pull the head 
back to track zero and "chatter" as it hits the head stop, then advance to 
where track 18 should have been. The red LED will flash because of the drive 
read error. No error message will be shown on the screen, but if you read the 
disk error channel, it will display: 21,READ ERROR,18,00. More on this later...
 FORMAT OR DISK "NEW": When you format a disk, the spindle motor will turn 
and the red light will come on. The drive will pull the head back to track 
zero and "chatter", then the stepper will advance to each track as it writes 
from track 1 to track 35. When it finishes the format (about 1 minute 25 
seconds on a stock drive), the head will return to track 18 (the directory). 
If the format fails, the red activity LED will flash, but there will be no 
error message on the screen. Reading the drive error channel will display: 
21,READ ERROR,00,00. Format failures can be caused by write protect (disk tab 
open), drive door open, bad disk, bad or clogged head, or bad chips in the 
drive. The format will attempt to write to track 1, then do a read, and if the 
read fails, the format will terminate, and the head will not move from track 
1. If it advances a few tracks and then stops or takes a long time to format, 
suspect a bad disk or an intermittant connection to the head. If the drive 
will read OK but fails to format a disk, check the head, UC1, UC2, UA1, and 
UD2. Swap out drive mechanics to verify the head is bad. It may test good 
with an ohmmeter and read disks OK, but if defective, may fail to format a 
disk. Note that all wires of the head should measure continuity (low 
resistance) to each other. If any line is open, the head is bad. Disconnect 
the plug from the drive to do the resistance tests and make sure you get the 
plug back on the connector the same way it came off. For write-protect 
problems, check UC1, UC2, UA1 and, of course, the sensor.
     As mentioned above, it is sometimes helpful to read the disk drive error 
channel when the drive red light is flashing. Here is a small BASIC program 
to do that. It reads the channel, displays the error message, and turns the 
red activity LED off. 
 10 OPEN 15,8,15 
 20 INPUT#15,EN,EM$,ET,ES 
 40 CLOSE 15
This program and all of the possible drive error messages are listed in the 
back of the disk drive operators manual. Note that JiffyDOS provides an easy 
way to check the error channel... just press the @ key, then hit RETURN.


     Lets take it from the top. Does the drive start up properly when turned 
on? If the power light (green LED) doesn't come on, or is dim or flickers, you 
probably have a power supply problem... the 5 volt line is bad. That usually 
results in a spindle motor that runs continuously with red LED off. Check the 
bridge rectifier (CR3 in early version drives with PCB# 1540050, and CR1 in 
later version drives with PCB# 251830) and the 5 volt regulator VR2. Note: if 
the regulated 12 volt supply fails, the motors will not run at all. That's a 
rare failure.
     At power up (without the computer connected) if the red activity LED 
stays on and the motor runs continuously, it means that the drive failed to 
complete its startup sequence. The most common causes are a bad DOS ROM UB4 
(901229-xx) or failing 5V bridge rectifier. The easiest place to check for 
correct voltages in and out of the power supply regulators is at the diodes 
CR2 and CR4 located near the two rectifiers. The anodes of those diodes are 
connected to the outputs of the +5V and +12V regulators. The cathodes 
(designated by a line or stripe at one end) show the unregulated source from 
the rectifiers that feed the regulators. 
     With drive startup problems, some chips to check are: UC4 (6502 MPU) and 
UC2 (6522 VIA). The smaller "glue logic" chips are pretty rugged, but do 
sometimes fail. Check UA1 (74LS14) and UD2 (7407)... they have also been known 
to cause those symptoms.


     When the computer is turned on, the reset signal from the computer should 
cause the drive (and other periferals like the printer) to reset. The red LED 
and spindle motor should come on and go off within a few seconds. If that 
doesn't happen, try a substitute serial cable. If that's OK, suspect the 
interface chips in the computer or VIA chip in the drive. If the computer 
resets other periferals, it's probably OK. Note that a drive may stay in reset 
(red LED on and spindle turning) if connected to a computer that is turned off. 
That's normal.
     If the computer can't "see" the drive on the serial bus, (serial cable 
unplugged or drive turned off, for example) you will immediately get an error 
message: "DEVICE NOT PRESENT" when you try a LOAD command, and the red LED 
will start flashing. 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 with LOAD"$",8 you will get that error message but 
LOAD"$",9 will work. If the VIA (UC3) 6522 interface chip in the drive is bad, 
the drive will likewise be "invisible" to the computer and you'll get "DEVICE 

     If you get "SEARCHING FOR" and nothing else happens, check ICs UB1 (7406) 
and UA1 (74LS14). These two chips carry data to and from the VIA chip. When 
one of them fails, if you try to load the directory or a program, the computer 
will display that error message until you turn it off or reset it. 
 74,DRIVE NOT READY,00 00 from the drive error channel indicates the computer 
can "see" the drive on the serial bus, but 1. there is no disk in it, 2. the 
disk is not formatted, 3. the drive door is not closed, 4. the read/write head 
is completely clogged or 5. the drive has an electrical problem. With any of 
these problems, the drive head can't find -any- data. The drive will respond 
by flashing its red activity LED and may step the head back and forth slightly 
looking for data. Note that this takes only a second or two before the drive 
"gives up" and the spindle stops. 
     A partially clogged R/W head may allow the drive to see data but still 
not read it properly. Other similar false reads would include a corrupted 
disk or trying to load the directory of the reverse side of a 1571 formatted 
disk. In any case, if the drive can see data but can't read it properly, it 
takes some time "hunting" before it gives up trying... more time than if it 
doesn't see any data. That's an important clue. You may hear the head assembly 
"chatter" as it bangs against the head stop searching for track zero... a 
normal process if disk errors are encountered. 


     One quirk of the 1541 is the "drive lost" symptom. Normally, the drive 
will "park" the head over the directory track (18). If the head, for some 
reason, gets stuck past the directory track, an INITIALIZE command from the 
computer 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 can exiting incorrectly from some programs by just turning off the 
computer. So, if the computer can access the drive, but you can't load even 
the directory of a known good disk, try the INITIALIZE command (with or 
without a disk inserted), then try reading A disk again. To INITIALIZE the 
As an alternative to Initializing, you could try formatting a disk. That will 
also return the head to track zero. Lastly, if you insert the original CBM 
transit card shipped with the drive (drive turned off) it will push the head 
back to track zero. Inserting a disk will not do it. The transit card has a 
tab on the front (the longer of the two tabs if there are two) that moves 
the head back. Don't have your transit card? With the top cover off and metal 
shield (if your drive has one) removed, you can push the head assembly back 
with your finger. The drive must be turned off, of course, or the head 
assembly will not move. The transit card is preferred to Initialize or Format 
as you don't have to turn off the computer (just the drive) so you don't lose 
a program in memory.


     If your computer setup or components have been moved recently, take note: 
drives or cables too close to a TV or monitor can sometimes pick up 
interference from the high voltage circuits inside the monitor which can 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 the drive and it still doesn't work (can't
read a disk), it may be out of alignment. Keep in mind that actual alignment 
problems are not as common as once thought. 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, then misalignment is a 
good possibility. There is one other thing you should check first: see if the 
head assembly rails are sticky, especially on a drive that has sat unused for 
a long time. With power off, the head assembly should slide back and forth 
easily and the tension band should be taut. If the rails seem sticky 
(experience helps to know the difference between good and bad), the rails 
should be cleaned with strong solvent (acetone, MEK, paint thinner, even 
WD-40 works) and either run dry or relubed with a tiny amount of graphite 
or silicone lube. Oil on the rails will work for a time, but it eventually 
picks up dirt and the rails will get sticky again. Avoid the use of spray 
cans in a drive. The spray goes everywhere. Spray a small amount of solvent on 
a Q-tip (cotton swab) and then wipe the rails, work the head assembly back and 
forth, clean the rails again, and repeat as necessary until no more residue is 


     Drive misalignment is something that doesn't usually happen all at once. 
It's normally a gradual process that begins with occasional disk errors (bad 
disk or intentional errors from copy protection) while loading (red LED 
flashing), failure to work with some programs, or excessive head chatter (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 chatter against the 
track zero stop repeatedly. If the alignment is far enough off, you will get 
"FILE NOT FOUND" and red LED flashing with all disks, and the drive may try 
several times before "giving up". Note that misalignment will cause read 
errors with known good disks but such a drive will probably still be able to 
format a disk and read it back again. A disk formatted on a misaligned drive 
will not read properly on a correctly aligned drive. 
     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 of course realignment requires disassembly.
I always final-check my drives with several different program disks to verify 
alignment... any commercial program disk can be used to do that. 
     Drive speed can drift over time, but it's rather rare to find it off far 
enough to cause problems. Spindle speed (Note: some drives have no adjustment) 
is reset with a small screwdriver adjustable control on a small PC board near 
the spindle motor. On older belt-driven spindle motors, the belt may be 
slipping. On all drives, the spindle collar (clamper) can get sticky and a 
tiny bit of lube helps. Don't overdo lubrication. Excess oil will be thrown 
off and could get on the disks. 
     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 securely. You can bend the tab down -slightly- (Newtronics drives 
only) so it makes more firm contact if necessary. A slipping or stalling 
disk will produce random read and write errors, a problem that's very hard 
to track down. Some disks may work better than others. The DD ones without a 
hub ring seem to slip more easily. HD disks should never be used in a 1541. 
     Bad (sticky) old grease on an ALPS drive can stall the spindle motor. If 
that is suspected, you must remove the metal bar that the hub lock is mounted 
on (two screws in the back) and take apart the clamper assembly by removing 
the C clip. It has half a dozen assorted washers, a brass bushing and a 
spring along with the plastic hub. Don't allow any of the spring-loaded parts 
to fly off when you remove the C clip. These parts need to be cleaned with 
solvent and put back together in the same order as before. A bit of moly lube 
or light oil finishes the job. Make sure the hub clamper is centered on the 
spindle before you fully tighten the rear screws. 

Ray Carlsen
CARLSEN ELECTRONICS... a leader in trailing-edge technology.
Questions and comments are welcome, especially if you spot a mistake
here. Thanks!