Apple Hard Disk SC Troubleshooting Guide
The Apple Hard Disk 20SC, 40SC, 80SC and 160SC share a case, power supply and fan, so Apple diagnosed them with one set of flowcharts. The tables here follow Apple's Technical Procedures for the SCSI hard disk drives, with the problems Apple published in its owner's guide and Tech Info Library.[1] Take-apart steps are on Apple Hard Disk SC General Maintenance.
Warning: the power supply runs from mains voltage, and Apple warns that the drive's high-voltage components keep their charge after switch-off. Unplug the drive before opening it.[2]
Before you start
[edit | edit source]Apple's points to remember:[1]
- Back up everything readable. Reinitialising a drive erases it permanently.
- Use known-good software and a known-good computer for testing.
- After fitting a new hard disk assembly, initialise it and copy the data back.
- The LED on these drives is off when the drive is ready. If it stays on or keeps flashing, the hard disk assembly is probably bad.
- Replacement mechanisms ship with terminating resistor packs for internal use. In an external case they must be removed, so a sluggish or dead drive after a mechanism swap calls for a check of the resistor packs.
Macintosh: Apple's flowchart
[edit | edit source]Apple's materials for this flowchart are a Macintosh test station, the MacTest disk for that Macintosh, the Macintosh Hard Disk Test disk, a DIN-8 serial loopback connector and a SCSI loopback card.[1]
- Rule out the Macintosh. Run the SCSI port loopback test on a Macintosh Plus, or the logic board test on other models. The test does not find bad SCSI connectors, so inspect the pins and solder joints of the Macintosh's SCSI connector too. If the test fails, Apple's cure is the Macintosh logic board.
- With the drive's case top off and the computer still switched off, plug in the drive, connect it and switch it on. You should hear the drive whir and see the fan turn.
- Watch the LED. It should go out within 15 to 20 seconds; it is lit only while the heads move.
- Run the Macintosh Hard Disk Test diagnostic. If it passes, run Disk First Aid, back up, reinitialise and restore the data.[1]
| Symptom | Apple's actions, in order |
|---|---|
| Drive or fan not running | Check the cable connections; replace the power supply; replace the fan. |
| LED still on after 15-20 seconds | Check the resistor packs; replace the hard disk assembly; replace the HDA-to-case cable. |
| Hard Disk Test fails, external drive (first time) | Replace the HDA-to-case cable; replace the SCSI select cable. |
| Hard Disk Test fails, internal drive (first time) | Check the resistor packs; check the cable connections; replace the SCSI power cable; replace the 50-pin SCSI cable. |
| Hard Disk Test fails a second time | Try Disk First Aid and back up what you can; replace the hard disk assembly; reinitialise it and restore the data. |
The Macintosh Hard Disk Test
[edit | edit source]Apple's Macintosh Hard Disk Test (version 2.1 or later in the 1990 procedures) tests any Apple SCSI drive, and also the non-SCSI Apple Hard Disk 20 from a Macintosh 512K, 512K enhanced, Plus, SE or Portable. Do not fit a SCSI loopback card while testing a drive, because it stops the SCSI bus from working normally.[1]
| Test | What it does | Time |
|---|---|---|
| Bad Block Scan | Reads every block, remapping bad blocks it finds. The only test that reads the whole drive; run it on every drive. | Up to 20 minutes |
| Random Seek | Reads a percentage of blocks in random order to check the seek mechanism | Up to 2 minutes |
| Exterior Track Seek | Seeks the outermost track from progressively nearer the centre | 2 minutes |
| Interior Track Seek | Seeks the innermost track from progressively nearer the edge | 2 minutes |
| Write Test | Reads, scrambles, rewrites and rechecks a random selection of blocks. It restores the data on a working drive, but can destroy data on a faulty one. | 10 minutes |
| Verify Partition Map | Checks the partition map. A damaged map means reformatting and repartitioning with HD SC Setup. | |
| Termination Power Test | Checks reliable reading and transfer from the drive. A drive that passes everything else but fails this test intermittently usually has a termination problem. |
If a drive keeps giving trouble after the Bad Block Scan has remapped its bad blocks, Apple's advice is to reformat it. Looping mode repeats the selected tests until stopped, for intermittent faults.[1]
Apple IIe and IIGS
[edit | edit source]Apple tests the drive from an Apple IIe or IIGS with the Apple II SCSI Diagnostic disk, a SCSI Interface Card and a SCSI loopback card.[1]
- Test the SCSI Interface Card on its own first, in slot 2 with the loopback card fitted. If it fails, replace the card. Apple warns that some SCSI card ROMs cause unexplained crashes on the IIGS while still passing the test.
- Power the drive with its case top off, not yet connected to the card. Listen for the drive and check the fan. If it does not run, replace the power supply, then the fan, then the drive.
- If the LED stays lit after 15 to 20 seconds, replace the drive, then the power supply, then the drive-to-case cable, then the SCSI select cable.
- Connect the drive to the card, start from the latest System Utilities disk and catalogue the drive. If it catalogues, run the Apple II Hard Disk Test; if it fails, exchange the drive. If it will not catalogue, format it from System Utilities, and exchange the drive if that fails.[1]
Warn the owner first: the repair step in the Apple II diagnostic can leave some data unreadable, and a reformatted or exchanged drive needs all applications and files reinstalling.[1]
An unenhanced Apple IIe cannot start up from a SCSI drive, though it can use one after starting from another disk; Apple's fix was the Apple IIe Enhancement Kit.[3] To start up from a SCSI drive on an Apple IIe, the SCSI card must be in a higher-numbered slot than any other card, and the drive's select switch set lower than the card's priority.[1]
Owner-level problems
[edit | edit source]| Symptom | Probable cause | Action |
|---|---|---|
| No fan noise when switched on | Cables, power cord or switch | Check all cables, the power cord and the power switches. |
| No drive icon on the Macintosh desktop | Drive not initialised; second drive switched on too late; damaged System file or driver | Initialise a new drive. With two or more drives, switch both on and wait at least 10 seconds before the Macintosh. Replace the System Folder from the installation disk, and if that fails, use the Installer's Update button on the right SCSI device number to replace the driver. |
| "Drive selection failed" in the Installer | Drive off, or cables wrong | Switch the drive on; check the cables and the terminator. |
| "This drive is not working correctly. See your dealer." during initialisation | Hardware fault | Work through Apple's flowchart above. |
| Second drive's number missing when clicking Drive | That drive not connected properly or not switched on | Check its cable and power. |
| Disk contents damaged after a power cut | Power lost while the light was blinking | Reinitialise and restore from a backup. |
The 20SC Installer has its own drive test, about 4 minutes long, which does not affect the data on the disk. Apple suggests running it every month or so.[2]
Known faults
[edit | edit source]40SC and 80SC drives that will not start
[edit | edit source]Some Hard Disk 40SC and 80SC drives develop a start-up problem after a period of use: no normal whine at start-up, and the computer does not see the drive. Apple's cure was a new hard disk assembly, with this procedure to recover the data first:[1]
- Remove the hard disk assembly from the case (or from a Macintosh II or IIx), leaving it on its metal frame.
- Hold it with the circuit board facing you and, in one quick, sharp motion, rotate it counter-clockwise. This should let it start.
- Install the replacement drive in the customer's case and the faulty drive in a second case, daisy-chain both to a Macintosh, check that the faulty drive is recognised (repeat steps 1 and 2 if not), initialise the replacement and copy the files across. With only one case, copy the files to floppy disks instead.
Quantum 3.5-inch 40 MB and 80 MB boot problems
[edit | edit source]Some Quantum 3.5-inch 40 MB and 80 MB drives boot intermittently, showing a disk icon with a flashing question mark or a "Cannot Load Finder" dialog. Only drives with variation codes 0032, 0034 and 0058 are affected; the code is on the small bar-code label at the SCSI connector end. Apple's fix replaced the ROM at U201 (version 7.9 01) with PROM TA.2 01 (part 341-0768), fitted with its notch towards the 50-pin SCSI connector.[1] On external drives, take the metal mounting bracket off the drive to reach the ROM. If the drive still fails after the new PROM and two or three power cycles of about 30 seconds off, Apple treated it as a different fault and exchanged the drive.[1]
20SC controller EPROM for the Macintosh II
[edit | edit source]One version of the 3.5-inch 20 MB drive must be upgraded from revision 2.6A to work in a Macintosh II or IIx. Check the 28-pin EPROM at U12: if it is labelled 2.6A, replace it with the upgrade EPROM, notch towards the 50-pin SCSI connector.[1]
Termination
[edit | edit source]Apple's article on a Macintosh IIci that would not start with an external Apple 160 MB drive attached gives the checks in order: drive switched on before the Macintosh, SCSI ID from 1 to 6, the drive tried on a second Macintosh without an internal drive, and the cable and terminator swapped.[4] On the 20SC, Apple's owner's guide and its SCSI cable manual placed the terminator differently; both work, and Apple recommended a terminator on the input of the first device plus one on the last device where there is more than one device or more than 10 feet of cable.[5]
Power supply
[edit | edit source]The supply (661-0343) is the same in all four models.[1] Adam Wilson, rebuilding the supply from a 1988 20SC, replaced all its electrolytic capacitors as a precaution, describing them as generally reliable, and found two 3.3 Ω 1 W resistors on its daughterboard damaged by overheating.[6] See Apple Hard Disk SC Capacitor Replacement Guide and Capacitor Failure Symptoms.
Mechanism replacement
[edit | edit source]Adam Wilson fitted a BlueSCSI SD-card adapter in a 3D-printed caddy inside the original drive frame of a 20SC whose Seagate ST-225N had failed, keeping the case, power supply and fan, and wired the front LED as a power light.[6] For general drive work see Hard Drive Maintenance and Repair.
Related pages
[edit | edit source]- Apple Hard Disk SC General Maintenance
- Apple Hard Disk SC Capacitor Replacement Guide
- Apple Hard Disk 20SC
- Apple Hard Disk 40SC
- Apple Hard Disk 80SC
- Apple Hard Disk 160SC
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 Apple Computer, Apple Service Technical Procedures, Cross Family Peripherals, Volume One (PN 072-0230, 1991), SCSI Hard Disk Drives chapter, hosted as File:Apple Service Technical Procedures Cross Family Peripherals Volume One Apr 1991.pdf and described at Apple Service Technical Procedures Cross Family Peripherals Volume One. Basics, p. 1.10 (PDF p. 185): Apple II slot rules; Diagnostics, pp. 3.2-3.9 (PDF pp. 215-222): test versions, Macintosh Hard Disk Test and its selections; Troubleshooting, pp. 4.3-4.9 (PDF pp. 238-244): things to remember, Flowchart 1 and notes, Flowcharts 2A and 2B with notes; Additional Procedures, pp. 6.2-6.8 (PDF pp. 247-253): 20SC upgrade, hard disk startup problem, 40SC/80SC upgrade; IPL.3 (PDF p. 256): power supply 661-0343 and PROM 341-0768.
- ↑ 2.0 2.1 2.2 Apple Computer, Apple Hard Disk 20SC Owner's Guide (030-3138-A, 1986), hosted as File:Apple Hard Disk 20SC Owners Guide 1986.pdf and described at Apple Hard Disk 20SC Owner's Guide. Printed pp. 22-25 (PDF pp. 32-35): the high-voltage warning, problem descriptions and solutions, and testing with the Installer.
- ↑ Apple Computer, "Hard Disk 20SC: Can't Be Startup Device for Unenhanced Apple IIe", Tech Info Library article 7582, created 19 April 1991, in the archive.org collection Apple's Technical Information Library Articles, https://archive.org/details/APPLE_TIL_ARTICLES, file TIL00001_to_TIL60496.zip.
- ↑ Apple Computer, "SCSI Termination and External Hard Drives", Tech Info Library article 8140, created 14 May 1991, APPLE_TIL_ARTICLES collection (archive.org), file TIL00001_to_TIL60496.zip.
- ↑ Apple Computer, "Hard Disk 20SC: Connecting a terminator", Tech Info Library article 662, revised 29 September 1990, APPLE_TIL_ARTICLES collection (archive.org), file TIL00001_to_TIL60496.zip.
- ↑ 6.0 6.1 Adam Wilson, "1988 Apple 20SC External HDD Repair & Restoration", Adam's Vintage Computer Restorations, 25 January 2023, retrieved 2026-10-04.