THE 1571 (and 1571 in the DCR) * COMMON PROBLEMS AND SOLUTIONS 11-20-07.


           THE 1571 (and 1571 in the DCR) * COMMON PROBLEMS AND SOLUTIONS 
       includes chips vs symptoms for the stand-alone 1571 drive
               latest changes and corrections  11-20-07


I TAP ON THE DISK, THEN IT WORKS...
     This is such a common complaint, I put it here at the top of the 
list. Some users indicate that they must "tap on the disk after inserting 
it and closing the drive door" 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 problem can be caused by: 1. a sticky lifter mechanism, 
(see HEAD LIFTER) or 2. the ejector mechanism is not latching properly 
(see DISK EJECTOR). 

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 will not solve whatever problem
it was meant to, but 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.
     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. 
     Sometimes the lever releases prematurely when the drive door is 
closed. If that happens, you may hear a scraping sound as the spinning 
disk rubs the inside edge of the disk jacket. This problem can also cause 
a failure to read properly and can be "cured" by tapping on the disk after 
insertion and closing the door. You may hear the click of the ejector 
latching again. If the ejector is the problem, you can bend the slide 
plate down a bit at the spot where the tang on the slider engages the 
lower fixed plate. Don't bend it too far down or the slider will bind 
and disks will not eject at all. 

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 stepper rails, especially if they are contaminated and/or sticky with 
old grease. I use paint thinner, but caution must be used not to get any 
such solvent on plastic parts as it may attack the surface. Swab down the 
rails and move the head assembly gently back and forth (drive turned off, 
of course) to reach further into the tight spots. Alternate between 
swabbing and moving the assembly several times until the rails are clean. 
You can't get everywhere, but with solvent on the rails, just moving the 
stepper back and forth will dislodge the dirt and old grease that can 
then be wiped off. Let the solvent dry throughly. Although it's really 
not necessary, you can 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. As an alternative to solvent, you can use 
WD-40 on a Q-tip as a cleaner. Contrary to popular belief, it's not a 
lubricant, but it works well as a solvent on old sticky grease. 

ROM BUG: If your stand-alone (not the 128DCR drive) 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 on the drive controller board (under the
power supply). The power supply (metal can) 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 may be unplugged
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, although I've
heard that some will require cutting a bit of the cabinet at the drive
latch because it rubs on the latch shaft. Drives can be interchanged if
necessary as a diagnostic or to salvage a working mechanism from a bad
drive.

          Added notes for the 1571D (drive inside the C128DCR):  

     The socketed DOS ROM in the 128DCR is under the drive mechanism on the
motherboard at location U102. It's different than the one in the stand-alone
1571 and therefore should not be interchanged.
     If there is a problem with the drive in the C128DCR, you may get
"dumped" into the built-in monitor at boot time (when it tries to autoboot).
If that happens, the screen will show something like: U1:13 0 01 00. If you
are having problems with internal drive access, as a diagnostic, or to use
an external drive as device 8, you can disable the internal drive by
disconnecting the ATN line, pin 1 of IC U113 (74LS14). That will make the
internal drive "invisible" to the computer. That chip is under the drive
near the right front edge of the computer. If you cut the IC pin, leave
enough so that you can solder it back if necessary (cut it close to the
motherboard).

                          CHIPS VS SYMPTOMS

     A normal startup sequence is as follows: with drive disconnected from 
computer, power up shows a continuous red power LED, and the green status 
LED comes on and goes out within about 1 second. The spindle motor runs for 
about three seconds and then stops. The stepper moves the head slightly 
back and forth, then stops. Note that the spindle motor may continue to 
spin if the computer is connected but turned off... that's normal because 
it holds the reset line. Also normal is spindle running about 10 seconds 
after disk reads. When the drive startup sequence or other operation is not
normal, this information might help nail the problem down. I assume you 
have already checked the power supply for its +5 and +12 volt DC outputs. 

U1	MPU				6502
  Green LED on steady and spindle motor runs all the time, no movement of 
the stepper at turn on. No drive access, locks up computer.

U2	DOS ROM				310654-03
  Green LED on steady and spindle motor runs all the time, no movement of 
the stepper at turn on. No drive access, locks up computer.

U3	SRAM				M2128-xx or TMM2016
  When powered up, green LED flashes once per second continuously. No drive 
access, locks up computer.

U4	VIA, SPINDLE MOTOR CTRL		65SC22 
  Green LED stays dark at power up and spindle motor runs continuously. No 
drive access, locks up computer.

U5	MASTER OSC			251829-01
  Drive powers up normally but no read, DRIVE NOT READY error.

U6	CONTROLLER			251828-01 OR HD61J215P
  Green LED on steady and spindle motor runs all the time, no movement of 
the stepper at turn on. No drive access, locks up computer.

U7	HEAD AMP & STEPPER CTRL		251853-01 or M36A2U57

U8	logic				7406
  Normal looking startup (LEDs and motors) and computer resets drive but no 
access, 74 DRIVE NOT READY error.

U9	VIA				65SC22
  Normal looking startup (LEDs and motors) but no drive access although 
computer resets drive when turned on or reset, locks up computer. 

U10	logic				74LS74
  Normal looking startup (LEDs and motors) and read OK but no write or 
format.

U11	DISK CONTROL			WD1770 or WD1772
  Normal looking startup (LEDs and motors) but when computer boots, drive 
can't read disk and stepper moves head to track zero. Subsequent disk 
access shows 74 DRIVE NOT READY error and green LED flashes rapidly. 
NOTE: this bad IC can corrupt disks!

U12	logic				74F32
  Green LED on steady and spindle motor runs all the time, no movement of 
the stepper at turn on. No drive access, locks up computer.

U13	logic				74LS266
  Green LED on steady and spindle motor runs all the time, no movement of 
the stepper at turn on. No drive access, locks up computer.

U14	logic				7407
  Normal looking startup but no read in 1571 mode, reads in 1541 mode but 
no write or format (21 READ ERROR). Can also cause disk ID mismatch after 
disk swap.

U15	logic				74LS14
  Green LED on steady and spindle motor runs all the time, no movement of 
the stepper at turn on. Computer locks up.  

U16	logic				7406
  Normal looking startup but spindle doesn't run. Although computer resets 
drive, access shows DEVICE NOT PRESENT error.

U17	logic				74LS14
  Green LED on steady and spindle motor runs all the time, no movement of 
the stepper at turn on. Computer locks up.

U18	logic				74LS175
  Green LED on steady and spindle motor runs all the time, no movement of 
the stepper at turn on. No drive access, locks up computer.  

U19	logic				74LS241
  Normal startup but 1541 mode only (read, write, format OK), no 1571 mode.

U20	CIA				6526A or 8521
  No 1571 mode but normal startup, read, format and write in 1541 mode only. 

U21	RESET GENERATOR			T520D

U22	logic				74LS123
  Normal startup and read/write but format fails and locks up computer.

Y1	XTAL OSC			TCO-745A


Ray Carlsen
Carlsen Electronics 
Questions and comments are welcome, especially if you spot a mistake here.
Thanks!