THE 1571 * COMMON PROBLEMS AND SOLUTIONS    05-20-98

DOOR LATCH: The twist down latch has a pin that eventually works loose and
can fall out. That's what has happened if the latch flops around and will
not move the mechanism. Hopefully, it's still in the drive (rattling
around?) and can be recovered. If allowed to float around in there, it can
short something out and cause damage. It's a round silver metal shaft,
about 3/4" long and about 1/16" in diameter. If you can't find it after
taking the drive apart, the correct sized nail can be cut to fit and
installed as a replacement pin. The original, if still there, can be
reinserted and secured with a dab of superglue or contact cement... just
enough to keep it from sliding back out. It should be inserted just far
enough to engage the white plastic part of the latch mechanism... too far
forward, and it will scrape the metal part of the latch. Lube the
metal-to-metal parts of the latch while you're at it.

HEAD WIRES: The top head moves up and down when a disk is inserted and the
door latch is turned. The 5 connecting wires on the top head must be free
to move, but such movement will cause them to break eventually. Some
drives will have a bit of epoxy where the wires are soldered to act as a
strain relief. Note: wires can still break -inside- the insulation where
it can't be seen. If you pull -gently- on each one with tweezers, the
broken ones will be loose and pull apart easily. Looking down on the drive
head, with the front of the drive facing you, the color code of the wires
is as follows, from left to right: green, red, white, yellow, black. If
any of these wires are broken, the drive will still work in the 1541 mode
(bottom head only is used), but in 1571 mode, the top head will not
function properly. If any wires are broken, you will need to trim off some
insulation from each wire and resolder it. Because the repaired wires will
be a bit shorter, you should cut the ties holding the cable to allow more
freedom of movement for the remounted wires. Form a small loop in the
wires for maximum flexibility. Add a dab of epoxy or silicon sealer to the
wire ends to allow them to flex without breaking again. Loosely tie the
cable back to the head assembly. Open and close the drive door with a disk
inserted to see if the wires have enough slack to allow complete head
motion. If the wires are too tight, the head will not come all the way
down to the disk surface, and you will create intermittant read/write
problems. Also, if there is not enough slack in the wires, they will break
again in a short time. When you complete the repair to the wires, tie the
cable bundle back to the head with thread or string and a dab of glue.

HEAD MOUNT: In a 1541 disk drive, the disk is pressed against the single
read-write head by a felt pad. That spring-loaded pad is lowered onto the
disk when the door latch is pressed down. In the 1571, when you insert a
disk and lower the door latch, a head lifter mechanism releases, and the
spring-loaded top head is gently lowered down onto the disk. Both heads
thereby remain in intimate contact with both sides of the disk. The top
head is mounted by means of a thin flexible metal strip. This strip is
rather fragile and can be damaged by rough handling. Notice that the head
has only one "finger" (on the left side) to allow the lifter mechanism to
keep it raised. If shipped without a transit card or disk in place, the
head mount can be subjected to excessive twisting force because all the
weight of the head is on the finger. A downward shock can twist the head
mount and can possibly break it. The top head must sit straight and line
up with the bottom head. If the mount is bent or torn, the head will not
sit straight. You may notice that a spinning disk makes more noise than it
should... that's the sound of the top head scratching it.  Depending on
the severity of the misalignment, the drive may not be able to read the
top side of a disk (blocks over 664), the drive may not work even in 1541
mode, and/or disks may be damaged. If the head mount is only slightly
bent, it should be possible to straighten it by -gently- bending it back
into proper alignment.
     Some users put weights (like a penny) on the top head, or increase
the tension of the spring to provide more force. This is to be avoided... 
it will cause increased head and disk wear, and may not solve whatever
problem it was meant to, and may cause further damage. Better to find out
what is actually wrong, and fix that. See HEAD LIFTER

HEAD LIFTER: This mechanism prevents the top head from lowering except: 1) 
when a disk is inserted, and 2) the door latch is down. It's there to keep
the two heads from banging into each other. When a disk is inserted, it
pushes a small lever with a brass cone-shaped end (at the left middle side
of the drive) out from under the head lifter and allows the head to come
all the way down and press on the disk. The brass cone should slide
forward on the tab of the metal plate above it when a disk is inserted all
the way, and should move completely out of the way when the door latch is
closed.
     If the cone does not move far enough or if the metal plate is sticky,
the lifter will prevent the top head from being lowered all the way down
to the disk. The result may be intermittant operation of the drive in all
modes, but especially in the 1571 double-sided mode, when data is accessed
on the top side of the disk. It may take longer to read disks (the drive
will try several times until it gets a good read), or you may encounter
errors on that side of the disk.
     Some users indicate that they must "tap on the disk after inserting
it" to get the drive to work properly. Some report that they can hear a
"click" when they do that and then the drive works fine. This is likely an
indication that the lifter mechanism is sticking, and the mechanical
action of tapping on the disk causes it to move forward and lets the
lifter release.
     See if the cone-lever is sticking by pushing on it with a toothpick. 
It has a spring return and is hidden under the metal lifter plate when no
disk is there. When you insert a disk and close the door slowly, see if
the cone is pushed all the way back out of the way by the downward
pressure of the plate. If not, see if that spring-loaded metal plate is
free to move down by itself. Insert a disk, move the cone lever back out
of the way and pull up on the plate, then gently release it. It should
drop all the way and release the head. If not, the lifter plate probably
needs lube (oil) on both ends of the shaft. The cone lever may need
cleaning and/or lubrication if the lever itself is sticky, or it needs
lube at the contact point of the cone and the tab. I prefer Molytone
grease, available at electronics supply houses.  It stays where you put
it, is -very- slippery, and it will not get gummy like oil or other
greases. You should use only a small amount of grease on those parts.
     If someone tried to "adjust" the cone lever or the plate, one or both
may be bent, and bending may be necessary to straighten them again. The
cone should be pointing straight up and should be shiny with no burrs on
it. The tab above it should likewise be clean. Examine it's underside (the
contact point for the brass cone) for burrs or rough spots. A pencil
eraser works well as a polishing tool. If the drive has been "adjusted" by
repair attempts, you may need to compare it to a working drive to see how
everything -should- line up.
     Before you even think about bending anything in an attempt to fix
your drive, consider this: the drive worked for years from the factory the
way it was designed. Find out why it doesn't work and repair it correctly.
An easy way to tell if the head is hanging up on the lifter is to observe
the black plastic "finger" on the left side of the top head. With a disk
in the drive and the door closed, that finger should -not- be touching the
lifter mechanism at all. 

OPTICAL SENSORS: The 1571 has three infra-red activated sensors. If these
sensors becomes contaminated with dust or smoke residue, it can cause the
drive to malfunction. The TRACK ZERO DETECTOR is located at the right rear
of the drive head assembly. It is used during disk Formatting, Initialize,
and whenever the drive seeks track zero. If out of adjustment,
contaminated, or defective, it may cause the drive to "chatter" like a
1541 when the stepper hits the mechanical head stop. The INDEX DETECTOR
(just to the left of the spindle collar) checks the disk for the index
hole. Although not needed on a Commodore GCR drive, this sensor maintains
compatiblity with the MFM standard when the drive is used in that mode
(the index hole conincides with sector 1). The WRITE-PROTECT SENSOR at the
left front side of the drive senses disk change and write-protect status. 
It should be checked and/or cleaned if the drive will not format or write
to a disk, but otherwise works normally. Don't forget to check for a write
protect tab that may have fallen off a disk and got stuck at the sensor. 
     Sensors can be cleaned with compressed air (to remove dust) and/or a
Q-tip moistened (not wet) with alcohol (to remove residue from cigarette
smoke). Do not remove the mounting screws to gain access to the sensors...
you will upset the alignment. The index and write protect sensors are
accessable through the drive door area with the front cover removed from
the drive. The zero stop sensor is a tight fit... remove about half the
head from a Q-tip and it will work. You'll need to move the head forward
to get to the sensor. 

DISK EJECTOR: This mechanism should automatically eject the disk when you
open the drive door. Normally, when a disk is inserted, it pushes a
spring-loaded slide plate back which locks in place. When the drive door
is latched down, it triggers the release mechanism, but the plate remains
fixed in place until the drive door is opened again. The slide plate then
releases, the spring forces it backwards and it ejects the disk for the
user to grasp. You can hear each one of these actions if you listen
closely. If the drive does not automatically eject disks, check for a
bent, misajusted or sticking slide lever, or a missing, broken, or
dislodged spring. 

CLEANING AND LUBRICATION: The heads and stepper rails should be cleaned
periodically, especially if the drive is running in a smoky or dusty
atmosphere, or if old disks are used (shedding oxide onto the heads). Dust
can be blown out with compressed air. Since the upper head is on a rather
delicate swivil mount, a minimum of force should be used to clean it. Pull
the top head up gently (it will not go very far before it hits the stop),
just enough to get a Q-tip moistened with alcohol between the two heads.
Rotate the Q-tip between your fingers to wipe the heads. The easiest
access point is between the rails on the right hand side of the drive.
Alcohol works OK for heads, but a stronger solvent should be used on the
rails, especially if they are contaminated and sticky. I use paint
thinner, but caution must be used not to get any solvent on plastic parts
as it may attack the surface. Swab down the rails and move the head gently
back and forth to reach further into the tight spots. You can't get
everywhere, but with solvent on the rails, just moving the stepper back
and forth will dislodge the dirt that can then be wiped off.  Let the
solvent dry throughly and then relube the rails, using a small amount of
silicone or graphite lube, or just run them dry. Don't use oil... it will
attract dirt and get sticky again. 

ROM BUG: If your 1571 takes a long time to access a 1541 formatted disk,
suspect the early version drive ROM 3.0 (CBM # 310654-03) as the reason. 
The latest version from Commodore was V3.1 and was the one CMD used to
formulate their JiffyDOS ROM. If you're on the fence regarding adding
JiffyDOS to your system, here is one more reason. If you have access to a
burner, a ROM image for the upgraded CBM version 3.0 (CBM # 310654-05) is
available at ftp.funet.fi. 

POWER SUPPLY: The power pack inside the 1571 uses a switching type of
supply. It runs cool and rarely fails. If it does malfunction, it can be
replaced easily (one plug-in connector) or repaired by a competant
technician. If you disconnect the power supply, make sure you note how the
connector is oriented. If it is installed backwards, it will cause severe
damage to the supply and/or the drive electronics package. The four-pin
plug of the supply goes to a motherboard socket: CN1. Pin # 1 is marked on
the board. The correct orientation of the PS plug is: pin 1 = black, pin 2
= brown, pin 3 = black, pin 4 = red. It's wise to somehow mark any
connectors you remove to prevent mistakes when you put them back.

OTHER PROBLEMS: Because it runs cooler than a 1541, the 1571 rarely fails
because of chip problems. In the rare event of a malfunction, one thing
you can try is reseating the only socketed chip in the drive: the DOS ROM,
a 310654-03 at board location U3. The motherboard is under the power
supply, by the way. The power supply can be moved out of the way (four
screws) without disconnecting it. It will just fold up and over the drive
mechanics, but be mindful that the power connector will probably pull out
when you do that. Make sure you know how it goes back... don't get it
backwards! If any other chips are socketed (perhaps because the drive was
repaired before), try reseating them too.  Make sure the connections
between the drive and motherboard are properly seated when you're
finished. Remove and reinsert them to clean the contacts. The mechanism
for the stand-alone 1571 and for the internal drive in the 128D are the
same. They can be interchanged if necessary as a diagnostic or to salvage
a working mechanism from a bad drive.

Ray Carlsen CET
Carlsen Electronics 
email: rrcc@u.washington.edu or rcarlsen@i-link-2.net
Questions and comments are welcome, especially if you spot a mistake here.
Thanks!