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1541 CHIPS VS SYMPTOMS and DIAGNOSTIC TESTS
latest additions and corrections: 4-8-06
This list represents the most common versions of the 1541 in the
standard brown case with PC board numbers 1540050 (early ALPS
push-down door mechanism) and the 251830 and 251777 (Newtronics
twist door mechanism).
Although the very early "long board" (white case) 1541 is not
represented here, major chip functions are of course similar. That
drive used more TTL (so-called "glue logic") chips that were later
"integrated" into a single motor control IC. Although functionally
identical, newer drives such as the 1541C and 1541-II integrate more
functions into fewer more specialized IC's, making repair parts even
harder to find.
Although most of the chips in the different versions of the
standard brown case 1541 are the same, board layout and some chip ID
numbers may be different. To eliminate confusion, I will list the two
major versions of the drive separately.
At the end of this article, I will give you some troubleshooting
hints and things to look for when you are trying to pin down a
particular fault. Before suspecting IC chips, don't overlook more
common causes of problems such as dirty R/W heads. Always check the
"easy stuff" first.
*****************************************************************
1541 CHIPS VS SYMPTOMS
PCB# 1540050 (early version) with ALPS drive mechanism (1982)
UA1 74LS14 LOGIC
Partial failure common cause of "FILE NOT FOUND" error. Total
failure: when drive powered up, red LED stays on and spindle motor
runs continuously (check also UB4, UC2, UC4, UC5, UC6, UD3, and UD5).
UB1 7406 (M53206P) LOGIC
Partial failure most common causing "SEARCHING FOR" (also check
UC3), or "DEVICE NOT PRESENT". Total failure: drive may power up
normally, but will not reset when the computer is turned on.
UB2 TMM2016AP-10 16K RAM
TMM2116AP-15 or MB8128-15
When drive powered up, motor runs continuously and red LED flashes
slowly (about 1 flash every 2 seconds).
UB3 325302-01 DOS ROM
When drive powered up, red LED flashes 3 times repeatedly.
UB4 901229-03 or -05 DOS ROM
When drive powered up, red LED stays on and spindle motor runs
continuously. DOS ROM is a common failure. Check also UA1, UC2, UC4,
UC5, UC6, UD3, and UD5.
UC1 325572-01 MOTOR CONTROLLER
When drive powered up, red LED comes on and goes out, but spindle
motor does not turn. When LOAD attempted, spindle does not turn, red
LED flickers, screen displays "FILE NOT FOUND" and red LED flashes.
UC2 6522 VIA (MOTOR CONTROL INTERFACE)
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC4, UC5, UC6, UD3, and UD5.
UC3 6522 VIA (SERIAL INTERFACE)
Drive powers up and resets normally. When LOAD attempted, screen
indicates "SEARCHING FOR ...", but no motors run and red LED does not
light.
UC4 6502 MPU
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC5, UC6, UD3, and UD5.
UC5 74LS04 (74LS14) LOGIC
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC6, UD3, and UD5.
UC6 74LS00 LOGIC
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC5, UD3, and UD5.
UC7 74LS42P LOGIC (DECODER)
When drive powered up, motor runs continuously and red LED flashes
slowly (about 1 flash every 2 seconds). Red LED may stay on and/or
motor may stop.
UD1 7406 (M53206P) LOGIC
When drive powered up or reset, spindle motor runs momentarily, but
red LED doesn't come on. When LOAD attempted, screen indicates
"SEARCHING FOR ..." but red LED does not light, spindle runs
continuously, and screen shows "FILE NOT FOUND" error.
UD2 7417 LOGIC (R/W CONTROL BUFFER)
When drive powered up or reset, red LED comes on and goes out, but
spindle motor does not turn. If LOAD is attempted, red LED comes on,
stepper moves slightly, spindle doesn't turn, screen shows "FILE NOT
FOUND" and red LED flashes.
UD3 74LS86 LOGIC
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC5, UC6, and UD5.
UD4 9602 (8602) LOGIC (MMV)
Drive powers up and resets normally, but if LOAD is attempted,
spindle motor runs with red LED out. Screen displays "SEARCHING FOR
..." and stepper does not move. Check also UE6.
UD5 74LS197 (74177) LOGIC (TIMER)
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC5, UC6, and UD3.
UE4 LM311 COMPARITOR (READ LOGIC)
Powers up normally. When LOAD attempted, spindle turns and red LED
comes on, but "FILE NOT FOUND" and red LED flashes. Check also UF3
and UF4.
UE6 74LS193 (7417) LOGIC (BIN COUNTER)
Drive powers up and resets normally, but if LOAD is attempted,
spindle motor runs with red LED out. Screen displays "SEARCHING FOR
..." and stepper does not move. Check also UD4.
UF3 NE592N READ PREAMPLIFIER
Powers up normally. When LOAD attempted, spindle runs and red LED
comes on, but "FILE NOT FOUND" and red LED flashes. Check also UE4
and UF4.
UF4 NE592N READ AMPLIFIER
Powers up normally. When LOAD attempted, spindle runs and red LED
comes on, but "FILE NOT FOUND" and red LED flashes. Check also UE4
and UF3.
VR1 UA7812KC (LM340KC-12) +12 VOLT REGULATOR
Drive powers up "normally", but motors run slowly or not at all.
If that happens, drive access will produce a flashing red activity
LED and errors "file not found" or "drive not ready" on the error
channel.
VR2 UA7805KC (LM340KC-5.0) +5 VOLT REGULATOR
Green (power) LED dim, flickers, or does not come on at all, but
spindle may run continuously and red LED may be dark.
CR1 2 AMP 200V BRIDGE RECTIFIER (FOR +12V)
Drive appears to power up normally, but motors do not run. Should get
warm only if the drive is being accessed (motors running).
CR3 2 AMP 200V BRIDGE RECTIFIER (FOR +5V)
On power up, green and red LED's are dim or dark and spindle motor
runs continuously. May be intermittant and "die" after warmup. Part
runs very hot normally and is a common failure in this model.
******************************************************************
1541 CHIPS VS SYMPTOMS PCB# 251830 or 251777 with Newtronics drive
mechanism (1984)
UA1 74LS14 LOGIC
Partial failure common cause of "FILE NOT FOUND" error. Total
failure: when drive powered up, red LED stays on and spindle motor
runs continuously (check also UB4, UC2, UC4, UC6, UC7, UD3, and UD5).
UB1 7406 (M53206P or 7707) LOGIC
Partial failure common cause of "SEARCHING FOR" (check also UC3)
and "DEVICE NOT PRESENT" errors. Total failure: drive powers up OK,
but does not respond to computer... no reset or disk access.
UB2 TMM2016AP-10 16K RAM
TMM2116AP-15 or MB8128-15
When drive powered up, spindle motor runs continuously and red LED
flashes about once every two seconds.
UB3 325302-01 DOS ROM
When drive powered up, red LED flashes 3 times repeatedly.
UB4 901229-03 or -05 DOS ROM
When drive powered up, red LED stays on and spindle motor runs
continuously. DOS ROM is a common failure. Check also UA1, UC2, UC4,
UC6, UC7, UD3, and UD5.
UC1 325572-01 MOTOR CONTROLLER
When drive powered up or reset, red LED comes on and goes out, but
spindle motor does not turn. When LOAD attempted, spindle does not
turn, red LED flickers, screen displays "FILE NOT FOUND" and red LED
flashes.
UC2 6522 VIA (MOTOR CONTROL INTERFACE)
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC4, UC6, UC7, UD3, and UD5.
UC3 6522 VIA (SERIAL INTERFACE)
Drive powers up and resets normally. When LOAD is attempted, screen
indicates "SEARCHING FOR ...", but no motors run and red LED does not
light.
UC4 6502 MPU
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC6, UC7, UD3, and UD5.
UC6 74LS04 (7713) LOGIC
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC7, UD3, and UD5.
UC7 74LS00 LOGIC
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC6, UD3, and UD5.
UC8 74LS42 LOGIC
When drive powered up, spindle motor runs continuously. Red LED may
stay on, or flash three times and go out.
UD1 7406 (M53206P) LOGIC
When powered up, spindle motor runs momentarily, but red LED
doesn't come on. When LOAD attempted, screen indicates "SEARCHING FOR
..." but red LED does not light and spindle runs continuously.
UD2 7407 (7417) LOGIC (R/W CONTROL BUFFER)
When drive is powered up or reset from computer, red LED comes on
and goes out, but spindle motor does not turn. When LOAD is
attempted, stepper moves slightly, spindle doesn't turn, and error
message on screen is "FILE NOT FOUND" with flashing red LED.
UD3 74LS86 LOGIC
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC6, UC7, and UD5.
UD4 9602 (74123) LOGIC (MMV)
Drive powers up and resets normally, but when LOAD is attempted,
screen indicates "SEARCHING FOR ..." red LED does not light and
spindle runs continuously. Check also UE6.
UD5 74LS197 (74177) LOGIC (TIMER)
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC6, UC7, and UD3.
UE4 LM311 COMPARITOR (READ)
Drive powers up and resets normally. Spindle motor runs, stepper
moves slightly, but "FILE NOT FOUND" error, and red LED flashes.
Check also UF3 and UF4.
UE6 74LS193 (7417 or 7407) LOGIC (COUNTER)
Drive powers up and resets normally, but when LOAD is attempted,
screen indicates "SEARCHING FOR ..." red LED does not light and
spindle runs continuously. Check also UD4.
UF3 NE592N (LM592) READ PREAMP
Drive powers up and resets normally. Spindle motor runs, stepper
moves slightly, but "FILE NOT FOUND" error and red LED flashes. Check
also UF4 and UE4.
UF4 NE592N (LM592) READ AMPLIFIER
Drive powers up and resets normally. Spindle motor runs, stepper
moves slightly, but "FILE NOT FOUND" error and red LED flashes. Check
also UF3 and UE4.
VR1 UA7812KC (LM340KC-12) +12 VOLT REGULATOR
When powered up, green power LED comes on and red LED comes on and
goes out normally, but motors do not run (or move slowly). Drive
access will produce a flashing red activity LED and error messages
"file not found" or "drive not ready" on the error channel.
VR2 UA7805KC (LM340KC-5.0) +5 VOLT REGULATOR
Green (power) LED dim, flickers, or does not come on at all. Drive
appears dead, but spindle motor runs continuously.
CR1 2 AMP 200V BRIDGE RECTIFIER (FOR +5V)
Drive appears dead, but spindle motor runs continuously with both
green and red LEDs dim or dark. May be intermittant and fail after
warmup. This part normally runs hot and is a common failure item.
CR3 2 AMP 200V BRIDGE RECTIFIER (FOR +12V)
Drive appears to power up normally, but motors do not run. Should get
warm only if drive is accessed (motors running).
Notes: UC2, UC3, UB4, and regulators VR1 and VR2 run warm normally
and bridge rectifiers CR1 and CR3 run very hot if drive is
being accessed. Otherwise, only CR3 will get hot.
Newtronics drives (twist type door latch) normally run a bit noiser
(stepper chatter) than earlier ALPS (push down door) types.
*******************************************************************
DIAGNOSTICS... WHAT TO LOOK FOR
When you are troubleshooting a drive, it is important to observe it
closely (with the cover off) for symptoms. For example, note how the drive
motors and indicator LED's function when the drive is powered up, reset,
and accessed by the computer. When the drive is instructed to LOAD a
program, note whether the stepper moves, how much it moves, and if it
"chatters". Try various functions like Initialize and observe the results.
Sometimes the clues to a malfunction are subtle. In some cases, as many as
eight different chips can cause the same symptom.
If your drive suddenly goes "dead" and you can't read disks without
"FILE NOT FOUND" errors, try the Initialize command:
OPEN15,8,15 (assuming drive is device 8)
PRINT#15,"I0"
CLOSE15
This command (or formatting a disk) will return the heads to track zero
and may bring it "back to life". You can also use the transit card (if
you still have one) to push the head back (with the drive turned off, of
course). By resetting the drive with a card, you don't need to lose a
program running in the computer.
Another cause of a "dead" drive is failure of the 5 volt bridge
rectifier (CR3 in early version drives, CR1 in later drives). That part
normally runs hot and is a common failure in a 1541. When the 5 volt
supply fails, your symptoms are dim or dark red and green LEDs and drive
motor spins continuously. If the 12 volt supply fails, the motors will
not run. The easiest place to check for correct voltages in and out of
the 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.
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 light comes on and stays on, red activity
light comes on (and spindle motor turns) for about two seconds, then red
light should go out and motor should stop.
COMPUTER POWER UP (OR RESET): Drive red light should come on and go out,
and motor should start and stop within two seconds.
READ DIRECTORY: Insert known good disk and type: LOAD"$",8 and hit the
RETURN key. The disk should spin and the head should move to track 18 and
read the directory. The screen will show: SEARCHING FOR $. If it finds it,
the screen will say READY. If the disk read fails for any reason (drive
door open, unformatted disk, bad chips in the drive, etc.), the drive red
light will flash and an error message: FILE NOT FOUND will appear. If you
read the disk error channel, it will say: 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, it 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
light 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 say:
21,READ ERROR,18,00.
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
(directory). If the format fails, the red drive light will flash, but
there will be no error message on the screen. If you read the drive error
channel, it will say: 21,READ ERROR,00,00. Format failures can be caused
by write protect, 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 stops, suspect
a bad disk, or an intermittant connection to the head. If the drive will
read OK but fails to format a disk, check UC1, UC2, UA1, and UD2. Swap out
drive mechanics to check the head. It may test good with an ohmmeter and
read OK, but if defective, will fail to format a disk. 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 (for DOS V2.0) to do that. It reads the channel, displays the
error message, and turns the drive light off.
10 OPEN 15,8,15
20 INPUT#15,EN,EM$,ET,ES
30 PRINT EN,EM$,ET,ES
40 CLOSE 15
All of the possible drive error messages are listed in the back of the
operators manual. Note that JiffyDOS provides an easy way to check the
error channel... just press the @ key, then hit RETURN.
Ray Carlsen CET
CARLSEN ELECTRONICS... a leader in trailing-edge technology.
Questions and comments are welcome, especially if you spot a mistake
here. Thanks!
--------------------------------------------------------------------------
1541 CHIPS VS SYMPTOMS and DIAGNOSTIC TESTS
latest additions and corrections: 4-8-06
This list represents the most common versions of the 1541 in the
standard brown case with PC board numbers 1540050 (early ALPS
push-down door mechanism) and the 251830 and 251777 (Newtronics
twist door mechanism).
Although the very early "long board" (white case) 1541 is not
represented here, major chip functions are of course similar. That
drive used more TTL (so-called "glue logic") chips that were later
"integrated" into a single motor control IC. Although functionally
identical, newer drives such as the 1541C and 1541-II integrate more
functions into fewer more specialized IC's, making repair parts even
harder to find.
Although most of the chips in the different versions of the
standard brown case 1541 are the same, board layout and some chip ID
numbers may be different. To eliminate confusion, I will list the two
major versions of the drive separately.
At the end of this article, I will give you some troubleshooting
hints and things to look for when you are trying to pin down a
particular fault. Before suspecting IC chips, don't overlook more
common causes of problems such as dirty R/W heads. Always check the
"easy stuff" first.
*****************************************************************
1541 CHIPS VS SYMPTOMS
PCB# 1540050 (early version) with ALPS drive mechanism (1982)
UA1 74LS14 LOGIC
Partial failure common cause of "FILE NOT FOUND" error. Total
failure: when drive powered up, red LED stays on and spindle motor
runs continuously (check also UB4, UC2, UC4, UC5, UC6, UD3, and UD5).
UB1 7406 (M53206P) LOGIC
Partial failure most common causing "SEARCHING FOR" (also check
UC3), or "DEVICE NOT PRESENT". Total failure: drive may power up
normally, but will not reset when the computer is turned on.
UB2 TMM2016AP-10 16K RAM
TMM2116AP-15 or MB8128-15
When drive powered up, motor runs continuously and red LED flashes
slowly (about 1 flash every 2 seconds).
UB3 325302-01 DOS ROM
When drive powered up, red LED flashes 3 times repeatedly.
UB4 901229-03 or -05 DOS ROM
When drive powered up, red LED stays on and spindle motor runs
continuously. DOS ROM is a common failure. Check also UA1, UC2, UC4,
UC5, UC6, UD3, and UD5.
UC1 325572-01 MOTOR CONTROLLER
When drive powered up, red LED comes on and goes out, but spindle
motor does not turn. When LOAD attempted, spindle does not turn, red
LED flickers, screen displays "FILE NOT FOUND" and red LED flashes.
UC2 6522 VIA (MOTOR CONTROL INTERFACE)
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC4, UC5, UC6, UD3, and UD5.
UC3 6522 VIA (SERIAL INTERFACE)
Drive powers up and resets normally. When LOAD attempted, screen
indicates "SEARCHING FOR ...", but no motors run and red LED does not
light.
UC4 6502 MPU
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC5, UC6, UD3, and UD5.
UC5 74LS04 (74LS14) LOGIC
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC6, UD3, and UD5.
UC6 74LS00 LOGIC
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC5, UD3, and UD5.
UC7 74LS42P LOGIC (DECODER)
When drive powered up, motor runs continuously and red LED flashes
slowly (about 1 flash every 2 seconds). Red LED may stay on and/or
motor may stop.
UD1 7406 (M53206P) LOGIC
When drive powered up or reset, spindle motor runs momentarily, but
red LED doesn't come on. When LOAD attempted, screen indicates
"SEARCHING FOR ..." but red LED does not light, spindle runs
continuously, and screen shows "FILE NOT FOUND" error.
UD2 7417 LOGIC (R/W CONTROL BUFFER)
When drive powered up or reset, red LED comes on and goes out, but
spindle motor does not turn. If LOAD is attempted, red LED comes on,
stepper moves slightly, spindle doesn't turn, screen shows "FILE NOT
FOUND" and red LED flashes.
UD3 74LS86 LOGIC
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC5, UC6, and UD5.
UD4 9602 (8602) LOGIC (MMV)
Drive powers up and resets normally, but if LOAD is attempted,
spindle motor runs with red LED out. Screen displays "SEARCHING FOR
..." and stepper does not move. Check also UE6.
UD5 74LS197 (74177) LOGIC (TIMER)
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC5, UC6, and UD3.
UE4 LM311 COMPARITOR (READ LOGIC)
Powers up normally. When LOAD attempted, spindle turns and red LED
comes on, but "FILE NOT FOUND" and red LED flashes. Check also UF3
and UF4.
UE6 74LS193 (7417) LOGIC (BIN COUNTER)
Drive powers up and resets normally, but if LOAD is attempted,
spindle motor runs with red LED out. Screen displays "SEARCHING FOR
..." and stepper does not move. Check also UD4.
UF3 NE592N READ PREAMPLIFIER
Powers up normally. When LOAD attempted, spindle runs and red LED
comes on, but "FILE NOT FOUND" and red LED flashes. Check also UE4
and UF4.
UF4 NE592N READ AMPLIFIER
Powers up normally. When LOAD attempted, spindle runs and red LED
comes on, but "FILE NOT FOUND" and red LED flashes. Check also UE4
and UF3.
VR1 UA7812KC (LM340KC-12) +12 VOLT REGULATOR
Drive powers up "normally", but motors run slowly or not at all.
If that happens, drive access will produce a flashing red activity
LED and errors "file not found" or "drive not ready" on the error
channel.
VR2 UA7805KC (LM340KC-5.0) +5 VOLT REGULATOR
Green (power) LED dim, flickers, or does not come on at all, but
spindle may run continuously and red LED may be dark.
CR1 2 AMP 200V BRIDGE RECTIFIER (FOR +12V)
Drive appears to power up normally, but motors do not run. Should get
warm only if the drive is being accessed (motors running).
CR3 2 AMP 200V BRIDGE RECTIFIER (FOR +5V)
On power up, green and red LED's are dim or dark and spindle motor
runs continuously. May be intermittant and "die" after warmup. Part
runs very hot normally and is a common failure in this model.
******************************************************************
1541 CHIPS VS SYMPTOMS PCB# 251830 or 251777 with Newtronics drive
mechanism (1984)
UA1 74LS14 LOGIC
Partial failure common cause of "FILE NOT FOUND" error. Total
failure: when drive powered up, red LED stays on and spindle motor
runs continuously (check also UB4, UC2, UC4, UC6, UC7, UD3, and UD5).
UB1 7406 (M53206P or 7707) LOGIC
Partial failure common cause of "SEARCHING FOR" (check also UC3)
and "DEVICE NOT PRESENT" errors. Total failure: drive powers up OK,
but does not respond to computer... no reset or disk access.
UB2 TMM2016AP-10 16K RAM
TMM2116AP-15 or MB8128-15
When drive powered up, spindle motor runs continuously and red LED
flashes about once every two seconds.
UB3 325302-01 DOS ROM
When drive powered up, red LED flashes 3 times repeatedly.
UB4 901229-03 or -05 DOS ROM
When drive powered up, red LED stays on and spindle motor runs
continuously. DOS ROM is a common failure. Check also UA1, UC2, UC4,
UC6, UC7, UD3, and UD5.
UC1 325572-01 MOTOR CONTROLLER
When drive powered up or reset, red LED comes on and goes out, but
spindle motor does not turn. When LOAD attempted, spindle does not
turn, red LED flickers, screen displays "FILE NOT FOUND" and red LED
flashes.
UC2 6522 VIA (MOTOR CONTROL INTERFACE)
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC4, UC6, UC7, UD3, and UD5.
UC3 6522 VIA (SERIAL INTERFACE)
Drive powers up and resets normally. When LOAD is attempted, screen
indicates "SEARCHING FOR ...", but no motors run and red LED does not
light.
UC4 6502 MPU
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC6, UC7, UD3, and UD5.
UC6 74LS04 (7713) LOGIC
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC7, UD3, and UD5.
UC7 74LS00 LOGIC
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC6, UD3, and UD5.
UC8 74LS42 LOGIC
When drive powered up, spindle motor runs continuously. Red LED may
stay on, or flash three times and go out.
UD1 7406 (M53206P) LOGIC
When powered up, spindle motor runs momentarily, but red LED
doesn't come on. When LOAD attempted, screen indicates "SEARCHING FOR
..." but red LED does not light and spindle runs continuously.
UD2 7407 (7417) LOGIC (R/W CONTROL BUFFER)
When drive is powered up or reset from computer, red LED comes on
and goes out, but spindle motor does not turn. When LOAD is
attempted, stepper moves slightly, spindle doesn't turn, and error
message on screen is "FILE NOT FOUND" with flashing red LED.
UD3 74LS86 LOGIC
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC6, UC7, and UD5.
UD4 9602 (74123) LOGIC (MMV)
Drive powers up and resets normally, but when LOAD is attempted,
screen indicates "SEARCHING FOR ..." red LED does not light and
spindle runs continuously. Check also UE6.
UD5 74LS197 (74177) LOGIC (TIMER)
When drive powered up, red LED stays on and spindle motor runs
continuously. Check also UA1, UB4, UC2, UC4, UC6, UC7, and UD3.
UE4 LM311 COMPARITOR (READ)
Drive powers up and resets normally. Spindle motor runs, stepper
moves slightly, but "FILE NOT FOUND" error, and red LED flashes.
Check also UF3 and UF4.
UE6 74LS193 (7417 or 7407) LOGIC (COUNTER)
Drive powers up and resets normally, but when LOAD is attempted,
screen indicates "SEARCHING FOR ..." red LED does not light and
spindle runs continuously. Check also UD4.
UF3 NE592N (LM592) READ PREAMP
Drive powers up and resets normally. Spindle motor runs, stepper
moves slightly, but "FILE NOT FOUND" error and red LED flashes. Check
also UF4 and UE4.
UF4 NE592N (LM592) READ AMPLIFIER
Drive powers up and resets normally. Spindle motor runs, stepper
moves slightly, but "FILE NOT FOUND" error and red LED flashes. Check
also UF3 and UE4.
VR1 UA7812KC (LM340KC-12) +12 VOLT REGULATOR
When powered up, green power LED comes on and red LED comes on and
goes out normally, but motors do not run (or move slowly). Drive
access will produce a flashing red activity LED and error messages
"file not found" or "drive not ready" on the error channel.
VR2 UA7805KC (LM340KC-5.0) +5 VOLT REGULATOR
Green (power) LED dim, flickers, or does not come on at all. Drive
appears dead, but spindle motor runs continuously.
CR1 2 AMP 200V BRIDGE RECTIFIER (FOR +5V)
Drive appears dead, but spindle motor runs continuously with both
green and red LEDs dim or dark. May be intermittant and fail after
warmup. This part normally runs hot and is a common failure item.
CR3 2 AMP 200V BRIDGE RECTIFIER (FOR +12V)
Drive appears to power up normally, but motors do not run. Should get
warm only if drive is accessed (motors running).
Notes: UC2, UC3, UB4, and regulators VR1 and VR2 run warm normally
and bridge rectifiers CR1 and CR3 run very hot if drive is
being accessed. Otherwise, only CR3 will get hot.
Newtronics drives (twist type door latch) normally run a bit noiser
(stepper chatter) than earlier ALPS (push down door) types.
*******************************************************************
DIAGNOSTICS... WHAT TO LOOK FOR
When you are troubleshooting a drive, it is important to observe it
closely (with the cover off) for symptoms. For example, note how the drive
motors and indicator LED's function when the drive is powered up, reset,
and accessed by the computer. When the drive is instructed to LOAD a
program, note whether the stepper moves, how much it moves, and if it
"chatters". Try various functions like Initialize and observe the results.
Sometimes the clues to a malfunction are subtle. In some cases, as many as
eight different chips can cause the same symptom.
If your drive suddenly goes "dead" and you can't read disks without
"FILE NOT FOUND" errors, try the Initialize command:
OPEN15,8,15 (assuming drive is device 8)
PRINT#15,"I0"
CLOSE15
This command (or formatting a disk) will return the heads to track zero
and may bring it "back to life". You can also use the transit card (if
you still have one) to push the head back (with the drive turned off, of
course). By resetting the drive with a card, you don't need to lose a
program running in the computer.
Another cause of a "dead" drive is failure of the 5 volt bridge
rectifier (CR3 in early version drives, CR1 in later drives). That part
normally runs hot and is a common failure in a 1541. When the 5 volt
supply fails, your symptoms are dim or dark red and green LEDs and drive
motor spins continuously. If the 12 volt supply fails, the motors will
not run. The easiest place to check for correct voltages in and out of
the 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.
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 light comes on and stays on, red activity
light comes on (and spindle motor turns) for about two seconds, then red
light should go out and motor should stop.
COMPUTER POWER UP (OR RESET): Drive red light should come on and go out,
and motor should start and stop within two seconds.
READ DIRECTORY: Insert known good disk and type: LOAD"$",8 and hit the
RETURN key. The disk should spin and the head should move to track 18 and
read the directory. The screen will show: SEARCHING FOR $. If it finds it,
the screen will say READY. If the disk read fails for any reason (drive
door open, unformatted disk, bad chips in the drive, etc.), the drive red
light will flash and an error message: FILE NOT FOUND will appear. If you
read the disk error channel, it will say: 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, it 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
light 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 say:
21,READ ERROR,18,00.
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
(directory). If the format fails, the red drive light will flash, but
there will be no error message on the screen. If you read the drive error
channel, it will say: 21,READ ERROR,00,00. Format failures can be caused
by write protect, 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 stops, suspect
a bad disk, or an intermittant connection to the head. If the drive will
read OK but fails to format a disk, check UC1, UC2, UA1, and UD2. Swap out
drive mechanics to check the head. It may test good with an ohmmeter and
read OK, but if defective, will fail to format a disk. 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 (for DOS V2.0) to do that. It reads the channel, displays the
error message, and turns the drive light off.
10 OPEN 15,8,15
20 INPUT#15,EN,EM$,ET,ES
30 PRINT EN,EM$,ET,ES
40 CLOSE 15
All of the possible drive error messages are listed in the back of the
operators manual. Note that JiffyDOS provides an easy way to check the
error channel... just press the @ key, then hit RETURN.
Ray Carlsen CET
CARLSEN ELECTRONICS... a leader in trailing-edge technology.
Questions and comments are welcome, especially if you spot a mistake
here. Thanks!