Atari 810 Drive Troubleshooting
Fault-finding on the Atari 810 starts with Atari's floppy quick-check and symptom table in the Atari 810 Disk Drive Field Service Manual (FS015854 Rev. 1), then moves to the voltage, clock and motor checks in Sams Computerfacts CD9, which also has a full schematic with DC voltages.[1][2] Both describe the original drive with a side board and a single rear board. Cleaning and adjustments are on the Atari 810 Maintenance Guide.
Before you start
[edit | edit source]- Use a working 9 V AC adaptor. Sams expects 10.9 V AC at the output plug.[2]
- Unplug the adaptor from the drive before connecting or disconnecting SIO cables.[3]
- Rule out user errors first. Atari's operator's manual lists a missing diskette, an open door, the wrong diskette, and a drive or peripheral that is not connected or not set to the right number.[4]
- If the drive keeps trying while the BUSY light is on, do not switch it off or open the door. Press SYSTEM RESET; if that does not stop it, disconnect the data cord at the drive, and the drive times out within about 20 seconds.[4]
- Try more than one diskette before blaming the drive.[5]
Floppy quick-check
[edit | edit source]Atari runs the quick-check before and after every repair. Switch the drive on and wait for the BUSY light to come on and go off; if it does not, check the connections and go to the symptom table. Then boot a write-protected master diskette, try to format it (ERROR-144 must appear), format a scratch diskette and check for 709 free sectors, write and delete files on it, and load and run a program from a diskette written on a known good drive.[1] The steps are listed on the maintenance guide.
Atari's symptom table
[edit | edit source]| Symptom | Possible cause | Corrective action |
|---|---|---|
| Drive will not turn on | Defective transformer; fault in the power switch and side board, or the power supply on the rear board | Replace the transformer; replace or troubleshoot the boards |
| Drive will not turn off | Defective side or rear board | Replace or repair the boards |
| Diskette does not turn | Belt off the flywheel or pulley, or broken; defective drive motor; clutch cone not clamping the diskette; fault in the drive motor circuit on the rear board | Refit or replace the belt; replace the motor; adjust or replace the clutch cone assembly; replace or troubleshoot the board |
| Diskette speed slow or varying | Tachometer lead out of place; write protect circuit bad; belt tension wrong; belt stretched; fault in the drive motor circuit on the rear board; spindle bearings seizing | Connect the green motor harness lead to the centre terminal of the write protect harness; replace the transport left side plate; adjust or replace the belt; troubleshoot the board; replace the spindle bearings |
| Diskette will not eject when the door is opened | Eject mechanism out of adjustment or broken; clutch cone to spindle clearance too small with the door open | Adjust or replace the mechanism; shim the clutch cone assembly |
| Front door will not open | Door latch out of adjustment or broken | Adjust or replace the latch |
| System will not boot | Speed wrong; cannot find track 00; fault on the side or rear board; stepper motor faulty; radial misalignment; bad head | Adjust the speed; adjust the track 00 stop setscrew; troubleshoot the boards; replace the stepper; align; replace the head assembly |
| Occasional read errors on all tracks | Damaged diskette; dirty or magnetised head; worn or dirty pressure pad; overstressed pressure pad arm spring | Replace the diskette; clean and demagnetise the head; replace the pad; replace the spring or head assembly |
| Read errors on the inner tracks | Speed wrong; fault in the read circuit | Adjust the speed; troubleshoot the rear board, side board or head, and check for a slow Q102 or Z104 on the side board |
| Read errors on the outer tracks | Speed wrong; fault in the read circuit | Adjust the speed; troubleshoot the boards or head, and check the value of R155 on the rear board |
| Drive will not write | Damaged diskette; fault in the write circuit | Replace the diskette; troubleshoot the rear board, side board or head |
| Various error codes | Electrical or mechanical faults | Check the diskette is not write-protected; replace Z105; troubleshoot the boards and transport |
| Drive incompatible with other drives | Speed wrong; radial misalignment | Adjust the speed; align |
| Drive writes on write-protected diskettes | Write protect circuit | Check the LED and phototransistor harness connections; replace the transport left side plate |
Best Electronics, which sells 810 parts, gives a rule of thumb: a drive that is dead, or lights its LEDs but does nothing mechanical, usually has a bad rear power board, sometimes together with a side board fault, while a drive that moves but gives boot errors or will not format usually has a mechanism fault.[6] It also reports that drives without the data separator board suffer read and write problems, and that the early single rear power board suffers speed problems.[6]
Power supply
[edit | edit source]The rear board rectifies the 9 V AC in a bridge (CR111 to CR114). A 7805 (A108) makes +5 V, a voltage doubler (CR115, CR116) feeds a regulator built around a TIP32A pass transistor (Q113) for +12 V, and a second doubler (CR117, CR118) feeds a 1N5231 zener (CR107) for -5 V, with the power LED (CR108) in series.[2][1]
| Point | Voltage |
|---|---|
| A108 (7805) input | 11.2 V |
| A108 output, +5 V source | 5.0 V |
| Q113 input, J105 pin 3 (doubler output) | 25.1 V |
| +12 V source | 12.0 V |
| -5 V source | -5.0 V |
Sams' order of checks:[2]
- Check for 10.9 V AC at the adaptor plug. If it is missing, replace the adaptor.
- With the drive on, check for 12.0 V at the cathode of CR111. If it is missing, check the power connector J110, the bridge diodes CR111 to CR114, and A108.
- Check for 5 V at pin 3 of A108. If it is missing, substitute A108; if it is low, substitute the error amplifier transistors Q114 and Q115.
- Check for 12 V at the collector of Q113. If it is missing, check the voltages and parts around Q113 and the doubler diodes CR115 and CR116.
- Check for -5 V at the anode of CR107. If it is missing, check CR107 and the power LED CR108.
The eight electrolytic capacitors on the rear board, including the three 4,700 µF filters, are listed in the Atari 810 Capacitor Replacement Guide.
Processor and clock
[edit | edit source]Sams checks the side board in this order:[2]
- Watch the reset line, pin 1 of the 6507 (A101), at switch-on. It should be low for about 0.2 seconds and then stay high. If not, check the reset transistors Q110 and Q111 and R175.
- Check for a 0.534 MHz waveform at pin 27 of A101. If it is missing, check for 1 MHz at pin 11 of Z101; if that is present, substitute Z101. If the 1 MHz is missing too, check the crystal X101 and the clock amplifier Q101.
- Check for activity on the data lines (pins 18 to 25) and address lines (pins 5 to 16) of A101. If there is none, check for 5 V at pins 3 and 4 of A101 and for the clock at pin 27.
The custom ROM (A102), 6810 RAM (A103), 6532 (A104) and FD1771 controller (A105) are the other large chips on the side board.[1] On drives with the data separator, that board plugs into the A105 socket.[2][7]
Drive motor
[edit | edit source]If the drive motor does not run, Sams checks:[2]
- Connector J103 for a good connection.
- 1.1 Ω between pin 3 of J103 and ground; if higher, check R139.
- The motor windings: 7.8 Ω between pins 3 and 4 of J103, 9.1 Ω between pins 4 and 5 of J103, and 178.5 Ω between pin 1 of J105 and pin 3 of J101. Replace the motor (M2) if they are wrong.
- Pin 25 of the 6532 (A104): about 0.1 V at rest and 5 V when the drive runs. Pin 14 of A104: low when running, high at rest. If these are wrong, substitute A104, the controller A105, the 6507 A101 and the ROM A102.
The motor speed control R142 and the motor drive array A107 are on the rear board; the speed adjustment is on the maintenance guide.[2][1]
Stepper motor
[edit | edit source]If the head does not step, check for 12 V at pins 1 to 5 of J102. If it is missing at pin 5, check for 12 V at pin 20 of J106. If it is missing at pins 1 to 4, measure the stepper windings: 75 Ω between pin 5 and each of pins 1 to 4 of J102. Replace the stepper if any winding is open.[2] The stepper is driven by four PIA lines through the MPSA06 drivers Q106 to Q109.[1][2]
Error codes
[edit | edit source]The drive reports faults through Atari BASIC and DOS error numbers. These are the input/output codes in Atari's list that concern the drive:[1]
| Code | Message |
|---|---|
| 138 | Device timeout |
| 139 | Device NAK |
| 140 | Serial bus |
| 142 | Serial bus data frame overrun |
| 143 | Serial bus data frame checksum error |
| 144 | Device done error |
| 145 | Read after write compare error |
| 160 | Drive number error |
| 162 | Disk full |
| 163 | Unrecoverable system data I/O error |
Error 144 is the expected result of trying to format a write-protected diskette in Atari's quick-check.[1]
Related pages
[edit | edit source]- Atari 810
- Atari 810 Maintenance Guide
- Atari 810 Capacitor Replacement Guide
- Atari 810 Documentation
- Floppy Drive Repair
- Capacitor Failure Symptoms
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Atari, Inc., Atari 810 Disk Drive Field Service Manual (FS015854, Rev. 1, July 1980): theory of operation pp. 2-3 to 2-20; floppy quick-check pp. 4-3 to 4-10; troubleshooting guide pp. 5-3 to 5-7; parts lists pp. 8-6 to 8-10; error codes p. 9-9. Hosted here as File:Atari 810 Disk Drive Field Service Manual FS015854 Rev 1.pdf.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 Howard W. Sams & Co., Computerfacts CD9, Atari Model 810 (June 1986): schematic with voltages and waveforms pp. 2-3; troubleshooting p. 12. Hosted here as File:Sams Computerfacts CD9 Atari 810 Disk Drive.pdf.
- ↑ Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, last modified 29 November 2009, section 3.4 (note by Rich Mier). faqs.org. Community reference.
- ↑ 4.0 4.1 Atari, Inc., Disk Drive Operators Manual (C014760, 1979), troubleshooting page. Hosted here as File:Atari 810 Disk Drive Operator's Manual C014760.pdf.
- ↑ Jason H. Moore, "Clean an 810/1050 Disk Drive Head (15-30 min)", Atari Projects, 4 August 2018. atariprojects.org. Community write-up.
- ↑ 6.0 6.1 Best Electronics, "8-Bit Drives" catalogue page, Atari 810 Tech Tip. best-electronics-ca.com. Atari parts vendor's service notes.
- ↑ Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, comp.sys.atari.8bit FAQ, last modified 2 August 2026, section 3.2.1. mcurrent.name. Community reference.