Atari XF551 Drive Troubleshooting
.jpg)
The Atari XF551 disk drive has a simple controller board and a linear power supply, both drawn in Atari's schematic C100727, feeding a standard PC-type drive mechanism.[1][2] Its known faults are recorded in the Atari 8-bit FAQ, in Atari's owner's manual and in Igor Gramblička's repair notes, the last being community experience.[3][4] Routine care is on the Atari XF551 Maintenance Guide and capacitor values are on the Atari XF551 Capacitor Replacement Guide.
Things that are not faults
[edit | edit source]- The drive does not move its head to track 0 when switched on, unlike the 1050. The head moves only when a disk is inserted and the latch closed.[2]
- There is no power light. The BUSY light comes on briefly at switch-on and then goes out.[4][3]
- The XF551 cannot format the back of a "flippy" disk that has only one index hole, and the Chinon version cannot read or write it either. The Mitsumi version reads and writes it but still cannot format it.[3][5]
- A few commercial disks, among them Flight Simulator II and Blue Max, do not load because the drive spins at 300 rpm instead of the 288 rpm of Atari's other drives.[6]
- The XF551 cannot copy disks protected against copying; Gramblička notes that a 1050 with a Happy or Speedy upgrade is still needed for those.[2]
Power and start-up
[edit | edit source]| Symptom | Probable cause | Action |
|---|---|---|
| Completely dead, no BUSY flash at switch-on | No AC from the adaptor; the adaptor's thermal fuse blown by a short at the drive's power inlet[2] | Measure 9 V AC at the adaptor plug. Replace or repair the adaptor; in future plug in with the adaptor switched off. |
| Dead, adaptor good | Worn power switch[2][7] | Check the switch for continuity; replace it. |
| Dead, switch good | Failed regulator or open rectifier | Measure the rails in the table below.[1] |
| Works when cold, stops after running for a while, works again after cooling | 7805 or 7812 reaching its thermal limit[2] | Switch off between sessions, add heatsinking or fit switching regulators; see the Maintenance Guide. |
| Erratic with a second drive | Two drives fed from one AC supply[2] | Give each drive its own adaptor. |
Measurements
[edit | edit source]| Point | Expected | Source |
|---|---|---|
| Adaptor output | 9 V AC | FAQ[3] |
| Input of Q5 (7805), across C103 | About 14 V DC | Gramblička[2] |
| Input of Q6 (7812), across C104 | About 23 to 26 V DC | Gramblička[8][2] |
| J5 pin 1 (drive power) | +5 V | Atari schematic[1] |
| J5 pin 4 and TP14 | +12 V | Atari schematic[1] |
| J5 pins 2 and 3 | Ground | Atari schematic[1] |
If +12 V is missing but +5 V is present, check the voltage doubler (C102, D2, D3) and C104 as well as Q6; the doubler is the only source of the 7812's input.[1]
Communication errors
[edit | edit source]| Symptom | Probable cause | Action |
|---|---|---|
| Boot error, or error 138 (device timeout) | Drive switched on after the computer; loose cable or adaptor plug; wrong drive number[4] | Switch the drive on first. Check the cables and set the drive select switches (both down for drive 1).[4][3] |
| Drive works only when the SIO cable is held or moved | Cracked joints or tracks at the SIO sockets[2] | Resolder the socket pins and screw the sockets to the board. |
| Drive answers as the wrong number or changes number | Dirty drive select switches[2] | Work the switches to and fro; replace them if they stay erratic. |
| Errors on a PAL computer with a drive from North America, or the reverse | Early firmware made in separate NTSC and PAL versions with slightly different transfer rates[2] | Fit firmware 7.7 or 7.7p, which works with both. |
Reading and writing
[edit | edit source]| Symptom | Probable cause | Action |
|---|---|---|
| Read errors on every disk | Dirty heads[2] | Clean the heads with isopropyl alcohol or spirit. |
| Rattle inside the drive; intermittent errors | Head shield fallen off the Mitsumi mechanism[2] | Find the shield, make sure it has not shorted the board, and glue it back. |
| One side of double-sided disks fails | Oxidised head cable connector on the mechanism board[2] | Unplug it, clean the contacts with spirit, dry and refit. |
| A second disk of a different density reads wrongly after a disk change | Firmware 7.7 does not detect the change of density[2] | Fit Bob Woolley's firmware 7.7p, or Hyper-XF with its disk-change microswitch. |
| Erratic behaviour that cleaning does not cure | Faded bits in the firmware EPROM[2] | Fit a freshly programmed EPROM. |
| Error 144 (device done) | Write-protected disk, unreadable sector or drive speed[4] | Remove the write-protect tab, try another disk. |
| Error 173 (bad sectors at format time) on several disks | Drive fault[4] | Clean the heads and check the mechanism. |
| Damaged diskettes | The XF551's heads press harder than other Atari drives; fragile, poor-quality disks suffer[3] | Use good double-density disks. |
Controller board or mechanism?
[edit | edit source]Gramblička describes a drive that began to boot, ran for about two seconds and then froze every time. Guides on the web blamed the head stepper motor. He tested the controller board with another mechanism and it worked, then swapped the electronics board on the original mechanism for a working one, after which the drive read, wrote and formatted normally; the stepper motor was good.[7] When a fault could be on either side of the 34-way cable, try the controller with another mechanism, or the mechanism with another controller, before replacing parts.
The mechanism is a standard 5.25-inch 360 KB PC drive at 300 rpm, so another PC drive can stand in. Gramblička warns that the cabling may not match, and that most other drives are longer and need the heatsink cut down to fit.[2]
Error codes
[edit | edit source]The DOS 2.5 manual's Appendix C gives these causes for the errors most often met with a disk drive.[4]
| Error | Name | Atari's explanation |
|---|---|---|
| 138 | Device timeout | The device did not respond in time: wrong drive number, drive not connected or not switched on. |
| 139 | Device NAK | Bad parameters, such as an unaddressable sector, or a garbled command; check the I/O cables. |
| 140 | Serial frame error | Garbled communication from the device; if it recurs, have the device or computer checked, and isolate it by removing peripherals one at a time. |
| 143 | Checksum error | Garbled communication on the serial bus; hardware or software. |
| 144 | Device done error | Write-protected disk, an unreadable sector, or variations in drive motor speed. |
| 173 | Bad sectors at format time | Use another diskette; if it happens with several, the drive may need repair. |
Related pages
[edit | edit source]- Atari XF551
- Atari XF551 Maintenance Guide
- Atari XF551 Capacitor Replacement Guide
- Atari XF551 Documentation
- Atari 1050 Drive Troubleshooting
- Floppy Drive Repair
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Atari (Japan) Corporation, Schematic Diagram XF551 (FCC), drawing C100727 rev. 1, sheet 1 of 2, preliminary release 19 November 1987: power supply, regulators Q5 and Q6, voltage doubler, connector J5 and TP14. Hosted as File:Atari XF551 Schematic C100727.pdf.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 Igor Gramblička (Igi), "Atari XF551 – doplnkové informácie / Atari XF551 – additional information", Igi blog, 26 March 2019 with later additions to September 2024, blog.3b2.sk (retrieved 2026-10-06), in Slovak. Community repair experience.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, last modified 2 August 2026, mcurrent.name (retrieved 2026-10-06). Section 3.2.3 (XF551 versions, flippy disks, drive select switches, fragile diskettes, busy light) and section 6.2 (9 V AC power supply). Community reference.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 Atari Corporation, Atari DOS 2.5: XF551 Disk Drive Owner's Manual, C033537-001, 1987. Section 1, pp. 1–4; boot errors, pp. 8–9; Appendix C, error messages, pp. 91–99. Hosted as File:Atari DOS 2.5 XF551 Disk Drive Owner's Manual C033537.pdf.
- ↑ Rich Tietjens, "Atari's New Super Disk Drive: First look inside the XF551", Antic vol. 7 no. 2, June 1988, atarimagazines.com (retrieved 2026-10-06). Formatting the reverse side of a flippy disk.
- ↑ Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, version of 29 November 2009 archived at faqs.org, section 3.4, faqs.org (retrieved 2026-10-06). Disks that do not load in the XF551 because of its 300 rpm speed.
- ↑ 7.0 7.1 Igor Gramblička (Igi), "Atari XF551 – ešte raz oživenie tejto jednotky / once again reviving this unit", Igi blog, 17 March 2020, blog.3b2.sk (retrieved 2026-10-06), in Slovak. Repair log including the mechanism-board fault.
- ↑ Igor Gramblička (Igi), "ATARI 1050, ATARI XF551 – napájací zdroj / Power Supply modification", Igi blog, 4 November 2013, blog.3b2.sk (retrieved 2026-10-06), in Slovak. Regulator input voltages.