1541 CHIPS VS SYMPTOMS 02-22-99 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... things to look for when you are trying to pin down a particular fault. ***************************************************************** 1541 CHIPS VS SYMPTOMS PCB# 1540050 with ALPS drive mechanism (1982) UA1 74LS14 LOGIC 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 Drive may power up normally, but will not reset from the computer. No drive access: "DEVICE NOT PRESENT" error. 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. 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 DIODE BRIDGE (RECT FOR +12V) Drive appears to power up normally, but motors do not run. CR3 2 AMP 200V DIODE BRIDGE (RECT FOR +5V) On power up, green and red LED's are dark and spindle motor runs continuously. May be intermittant and "die" after warmup. Part runs very hot... common failure in this model. ****************************************************************** 1541 CHIPS VS SYMPTOMS PCB# 251830 or 251777 with Newtronics drive mechanism (1984) UA1 74LS14 LOGIC 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 Drive powers up OK, but does not respond to computer... no reset or disk access. If drive accessed, "DEVICE NOT PRESENT" error. 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). 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 DIODE BRIDGE (RECT FOR +12V) Drive appears to power up normally, but motors do not run. CR3 2 AMP 200V DIODE BRIDGE (RECT FOR +5V) Drive appears dead, but spindle motor runs continuously with both green and red LED's dark. May be intermittant after warmup. Part normally runs very hot... common failure in this model. Notes: UC2, UC3, UB4, and regulators VR1 and VR2 run warm normally and diodes (bridge rectifiers) CR1 and CR3 run very 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:PRINT#15,"I0":CLOSE15 (assuming drive is device 8). This (or formatting a disk) will return the heads to track zero and may bring it "back to life". 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. All of the possible drive error messages are listed in the back of the operators manual. 10 OPEN 15,8,15 20 INPUT#15,EN,EM$,ET,ES 30 PRINT EN,EM$,ET,ES 40 CLOSE 15