Commodore 1571 Troubleshooting Guide
Introduction
The Commodore 1571 was Commodore's high-end 5¼" floppy disk drive. With its double-sided drive mechanism, it had the ability to utilize double-sided, double-density (DS/DD) floppy disks natively. This was in contrast to its predecessors, the 1541 and 1570, which could fully utilize such disks only if the user manually flipped them over to access the second side. (However, the two methods were not interchangeable; disk which had their back side created in a 1541 by flipping them over would have to be flipped in the 1571 too, and the back side of disks written in a 1571 using the native support for two-sided operation could not be read in a 1541).
The 1571 is generally a more reliable unit than its predecessors, and few cases of IC failure caused by heat have been reported due to the fact it tends to run cooler, even though it still has an internal power supply. Having said that, failures do still take place. This page hopes to assist you in locating the root cause of your 1571 issue(s).
The 1571 PCB
| Board Location | Purpose | Description |
| U1 | CPU | MOS 6502 |
| U2 | ROM | 32K x 8 DOS ROM - chip = MOS 310654-03 (old buggy ROM) or MOS 310654-04 (newer ROM that was released 12/05/86). |
| U3 | RAM | 2K x 8 Static RAM - various manufacturers |
| U4 | VIA | MOS 65SC22 or 65SC22A 2 MHz CMOS |
| U5 | Master OSC | 20-pin gate array - chip = 251829-01 |
| U6 | Controller | 40-pin gate array - chip = 251828-01 or HD61JS215P |
| U7 | Head amp & Stepper motor controller | R/W hybrid - 251853-01 or M36A2U57 |
| U8 | Logic | 7406 |
| U9 | VIA | MOS 65SC22 or 65SC22A 2 MHz |
| U10 | Logic | 74LS74 |
| U11 | Disk controller | WD1770-00 or WD1772 |
| U12 | Logic | 74F32 |
| U13 | Logic | 74LS266 |
| U14 | Logic | 7407 |
| U15 | Logic | 74LS14 |
| U16 | Logic | 7406 |
| U17 | Logic | 74LS14 |
| U18 | Logic | 74LS175 |
| U19 | Logic | 74LS241 |
| U20 | CIA | MOS 6526A (2 MHz) -or - MOS 8520 (2 MHz) - used only for fast serial access. When used in an unmodified C64, U20 is not in service. |
| U21 | PST | 520C/D Volt Detector |
| U22 | Logic | 74LS123 |
The following table outlines some common symptoms, the cause, and resolution:
NB: "Normal drive boot up" is as follows:
Red POWER light comes on and stays on, green DRIVE light comes on momentarily as well as spindle motor, then both DRIVE light and motor go off.
| Symptom | Cause | Resolution |
| Normal drive boot up, access to directory or loading results in no activity from drive (no motor spin-up, no rapid clicking, and no green DRIVE light), and FILE NOT FOUND ERROR or DEVICE NOT FOUND ERROR message | If DEVICE NOT FOUND error, make sure you are calling the correct device number, e.g. 8, 9, 10 or 11 according to the DIP switches on the back of the drive. If after LOAD"$",<device number> to get the disk's directory you get a mix of FILE NOT FOUND error and then DEVICE NOT FOUND ERROR, this could be a problem with your comope puter and not the drive itself. If possible test the drive and cable on another Commodore 64 or 128. If the drive works, you know its the computer at fault. |
Check DIP switch setting (table is further down this page here) |
| On boot up, green LED on steady and spindle motor runs continuously. No movement of stepper motor at power on. No drive access and computer locks up. | CPU at U1 is bad. DOS ROM at U2 is bad. Controller at U6 is bad. Logic chip at U12 is bad. Logic chip at U13 is bad. Logic chip at U15 is bad. Logic chip at U17 is bad. Logic chip at U18 is bad. |
Replace 6502 CPU at location U1, Replace DOS ROM at location U2. Replace Controller at location U6. Replace 74F32 logic chip at location U12. Replace 74LS266 logic chip at location U13. Replace 74LS14 logic chip at location U15. Replace 74LS14 logic chip at location U17. Replace 74LS175 logic chip at location U18. |
| Normal drive boot up, but no read in 1571 mode. Reads ok in 1541 mode but cannot write or format (READ ERROR displayed). Can also cause disk ID mismatch after disk swap. | Logic chip at U14 is bad. | Replace 7407 logic chip at location U14. |
| Normal drive boot up, but spindle doesn't run. Access to drive always shows DEVICE NOT PRESENT error. | Logic chip at U16 is bad. | Replace 7406 logic chip at location U16. |
| Normal drive boot up, but only works in 1541 mode (read, write and format ok). No 1571 mode. | Logic chip at U19 is bad. CIA at U20 is bad. |
Replace 74LS241 logic chip at location U19. Replace 6526A or 8521 chip at location U20. |
| Normal drive boot up, and read/write works ok. Format fails and locks up computer. | Logic chipat U22 is bad. | Replace 74LS123 logic chip at location U22. |
| On boot up, green LED flashes once per second continuously. No drive access and computer locks up. | SRAM at U3 is bad. | Replace SRAM at location U3. |
| On boot up, no green LED. Spindle motor runs continuously. No drive access and computer locks up. | VIA at U4 is bad. | Replace VIA at location U4. |
| Normal drive boot up, but no access (DEVICE NOT READY ERROR). | Logic chip at U8 is bad. | Replace 7406 logic chip at location U8. |
| Normal drive boot up, but computer locks up. | VIA at U9 is bad. | Replace 65SC22 VIA chip at location U9. |
| Normal drive boot up. Read ok, but writing or formatting fails. | Logic chip at U10 is bad. | Replace 74LS74 logic chip at location U10. |
| Normal drive boot up. Drive can't read disks and stepper motor moves head to track zero. Subsequent disk access shows DEVICE NOT READY and green LED flashes rapidly. | Disk controller chip at U11 is bad. | Replace WD1770 or WD1772 at location U11. |
| Takes a long time to read single-sided disks. Double-sided are quick. | You have the buggy ROM. The old ROM was buggy in that it has a hard time figuring out 1541-formatted single-sided mode and 1571 double-sided mode. | Upgrade the ROM to the Commodore new ROM or install a JiffyDOS kernal ROM |
| Only works single-sided, and cannot format successfully | Five coloured wires on the top head - one or more are loose or have become disconnected. | See 'HEAD WIRES' section further down this page. |
| Can format double-sided, but cannot read on second side | Upper drive heads are out of alignment. | Run the alignment program further down this page and try again. |
| Reading directory of a disk it just clicks rapidly, then the green light flashes repeatedly. No directory is displayed. In C64 mode, trying LOAD"$",8 returns 'FILE NOT FOUND' and green light flashes repeatedly. | Drive head may be jammed. The 1571 generally does not make a lot of noise the way the 1540/1541 did, unless the drive head is rammed into track 40 (near the centre of the disk). Another light sensor near the outer edge of the disk detects track 1, which is why you do not normally hear the head-banging you used to with the 1540/1541 drives (the sensor detects track 1 and stops the head to avoid banging). BUT.. there is no track 40 sensor ! | |
| Drive can be heard spinning continuously even when no disk is inserted | When you insert a disk into the drive it breaks a light beam. This is mainly used to test the write-protect tab, but it also serves to spin-up the drive motor. This helps the disk seat properly when you close the drive door. | |
| No disk spinning sound ever | Drive motor may not be working, or the drive belt is broken. | |
Detecting your 1571's ROM version
Here's a program which allows you to check which ROM version you have. It reports one of three versions: the old ROM, the new ROM, or the Cost-Reduced (CR) model.
10 OPEN1,8,15
20 PRINT#1,"M-R"CHR$(0)CHR$(192)CHR$(2):GET#1,A$
30 CLOSE1
40 A=ASC(A$+CHR$(0))
50 IFA=56THENPRINT"1571 WITH NEW ROM CHIP":END
60 IFA=66THENPRINT"1571 WITH OLD ROM CHIP":END
70 IFA=132THENPRINT"1571CR"
Head Alignment Program from RUN Magazine
0 REM REVERSE KNOCK YOUR DRIVE - STEPHEN CHEUNG
10 OPEN 15,8,15,"I"
20 SP=1:FORI=1 TO 100:GOSUB40:NEXT
30 FORI=1 TO 20:SP=-1:GOSUB40:NEXT:PRINT"ALL DONE!":PRINT#15,"I":CLOSE15:END
40 PRINT#15,"M-R"CHR$(0)CHR$(28):GET#15,A$:A=ASC(A$+CHR$(0)):BI=A AND 3
50 BI=BI+SP:BI=BI AND 3
60 R=(A AND 252) OR BI: PRINT#15,"M-W"CHR$(0)CHR$(28)CHR$(1)CHR$(R):RETURN
DIP Switch settings on the back of the 1571
The two DIP switches on the back of the 1571 unit configure how the drive appears (Drive 8, 9, 10 or 11) to the computer it's connected to:
| DIP1, DIP2 | Meaning |
| Up Up | Drive 8 |
| Up Down | Drive 9 |
| Down Up | Drive 10 |
| Down Down | Drive 11 |
Some other notes from around the web...
The top head moves up and down when a disk is inserted and the door latch is pulled down. The 5 connecting wires on the top head must be free to move, but such movement causes 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.