IBM PS/2 Model 70 Troubleshooting Guide
This guide documents fault diagnosis for the IBM PS/2 Model 70 (machine type 8570, all submodels). The Model 70 shares much of its POST architecture with the IBM PS/2 Model 50 / 60 but has 80386DX-specific and Power Platform-specific failure modes, and is uniquely afflicted by the SMD electrolyte leakage that defines the PS/2 plague.
Reference Diskette and Diagnostics
[edit | edit source]The Model 70 requires the Model 70-specific Reference Diskette. The Power Platform-equipped 8570-B21 / -B61 uses a different Reference Diskette image with BIOS extensions for the 80486 daughtercard. Reference Diskettes are not cross-compatible between PS/2 submodels.
Boot Options:
- F1 — boot the Reference Diskette (Set Configuration, Set Features, Display Configuration, Copy Option Diskette, Run Auto Configuration).
- Ctrl-A from the Reference Diskette menu — Advanced Diagnostics. Advanced Diagnostics for the Model 70 includes 80386-specific tests (paging, protected mode entry/exit, 32-bit data path) not run on the Model 50 / 60.
POST Sequence
[edit | edit source]The Model 70 POST runs in this order:
- Reset; CPU register check (80386 includes paging and protected mode tests).
- ROM checksum.
- CMOS / RTC battery check.
- Planar RAM count (with one beep at 640 KB).
- Onboard VGA initialisation.
- Floppy controller and drive seek.
- MCA adapter ID scan (each card returns a 16-bit ID).
- ADF lookup against CMOS configuration record.
- ESDI controller initialisation.
- Boot device selection.
A four-digit numeric code displayed top-left on the screen is a fault code from the test block currently running.
Beep Codes
[edit | edit source]| Beeps | Meaning |
|---|---|
| 1 short | POST passed; normal boot. |
| 2 short | Configuration error; numeric error on screen. |
| 1 long, 1 short | Planar fault. |
| 1 long, 2 short | Display adapter fault. |
| Continuous | Power supply or planar fault. |
| None, no display | Planar or PSU fault before video init. |
Numeric POST Codes
[edit | edit source]POST codes follow the IBM convention where the test block is the leading digit(s). The Model 70 shares the 1xx–10xxx code families with the Model 50 / 60 but adds 80386-specific tests.
1xx — Planar / System Board
[edit | edit source]| Code | Meaning | Notes |
|---|---|---|
| 101 | Interrupt failure | Planar IRQ controller fault. |
| 102 | Timer failure | |
| 103 | Timer IRQ failure | |
| 104 | Protected-mode failure | 80386 protected mode test failed. Often planar SMD cap leakage near the CPU. |
| 105 | Keyboard controller failure | |
| 106 | Logic gate / planar logic failure | |
| 107 | NMI failure | |
| 108 | Timer-bus timeout | |
| 109 | DMA test failure | |
| 110 | Planar parity check 0 | |
| 111 | I/O parity check | |
| 112 | Watchdog timeout | |
| 113 | DMA arbitration timeout | |
| 114 | Paging test failure | 80386-specific. |
| 121 | Unexpected hardware interrupt | |
| 151 | Real-time clock failure | RTC chip itself (not just the cell). |
| 161 | CMOS configuration empty | Dead RTC battery; replace DS12887 module. |
| 162 | CMOS checksum bad | |
| 163 | Time and date not set | |
| 164 | Memory size mis-match with CMOS | Run SETUP from Reference Diskette. |
| 165 | MCA adapter ID mismatch | Run Auto Configuration. |
| 166 | MCA arbitration failure | |
| 167 | Real-time clock failure |
A 104 on a Model 70 frequently indicates SMD electrolyte leakage near the 80386 CPU socket has corrupted address or control lines. Recap before any other diagnosis.
2xx — RAM
[edit | edit source]| Code | Meaning |
|---|---|
| 201 | Memory test failed (planar or memory adapter card) |
| 202 | Memory address line error |
| 203 | Memory address line error |
| 215 | Memory option-adapter failure (e.g., MCA Memory Adapter) |
| 216 | Memory option-adapter address conflict |
| 225 | Wrong memory speed for board (rare on Model 70) |
The 201 number is followed by the failed memory block address (8 hex digits). Use the address to identify the failing SIMM bank or MCA memory adapter slot.
3xx — Keyboard
[edit | edit source]| Code | Meaning | |
|---|---|---|
| 301 | Keyboard not responding | Wrong port? Try a known-good keyboard. |
| 302 | User-indicated keyboard error | |
| 303 | Keyboard / system unit interface fault | |
| 304 | Keyboard or system unit interface failed | |
| 305 | +5 V fuse on planar (keyboard fuse) | |
| 365 | Keyboard mouse problem (PS/2 ports) |
6xx — Floppy Drive
[edit | edit source]| Code | Meaning |
|---|---|
| 601 | Floppy / drive failure |
| 602 | Floppy drive boot record failure |
| 604 | Floppy diagnostic error |
| 611 | Floppy adapter / controller failure |
| 613 | Cable / drive A: failure |
| 621 | Drive seek failed |
| 622 | Drive CRC error |
| 624 | Floppy data bus addressing error |
| 626 | Floppy data compare error |
8xx — Math Coprocessor
[edit | edit source]The Model 70 (E61 / 121 / A21 / A61) supports an optional 80387DX coprocessor. The Power Platform B21 / B61 has the math unit built into the 80486DX.
| Code | Meaning |
|---|---|
| 801 | Coprocessor test failed |
104xx — ESDI Fixed Disk Adapter/A
[edit | edit source]The Model 70 uses the IBM ESDI Fixed Disk Adapter/A for its 60 / 120 MB ESDI drive. The 104xx error family is the same as on the Model 50 / 60 ESDI submodels.
See IBM PS/2 Model 60 Troubleshooting Guide for the complete 104xx code table — the same codes apply to the Model 70.
In summary:
- 10450 / 10451 / 10452 — drive-side errors.
- 10455 / 10499 — controller failure. Recap controller card before condemning.
- 10463 — write/read sector error. Same.
- 10464 — primary boot record read failure (drive or filesystem).
- 10480 / 10481 — drive 0 / 1 fatal error.
- 10491 / 10492 / 10493 — user-indicated read/write/controller error during Advanced Diagnostics.
Display POST Codes
[edit | edit source]The Model 70 has onboard VGA on the planar. The 2401 / 2402 / 24xx code family covers the planar VGA. A 24xx error is a planar / VGA fault — and on the Model 70 is one of the more common SMD electrolyte leak symptoms (electrolyte corrodes traces near the VGA controller chip first because they are the most densely-packed on the planar).
| Code | Meaning |
|---|---|
| 2401 | Onboard VGA POST failure |
| 2402 | VGA video memory failure |
| 2403 | VGA palette DAC failure |
| 2408 | User-indicated VGA failure (Advanced Diagnostics) |
| 2409 | VGA test failure |
| 2410 | Planar VGA card failure |
SMD Electrolyte Leak Diagnostic Workflow
[edit | edit source]The Model 70 / 80 planar's surface-mount aluminium electrolytic capacitors are the leading cause of "the Model 70 won't POST" complaints. A leaky SMD cap can produce:
- A 104 (protected mode) error if the leak is near the CPU.
- A 201 (memory) error if the leak is near the SIMM controller.
- A 2401 (VGA) error if the leak is near the VGA chip.
- Random, intermittent reboots if the leak is on a bus signal.
- No POST at all if the leak has shorted a power rail.
If a Model 70 is exhibiting any persistent or intermittent POST fault, inspect the planar for SMD electrolyte leakage before any other diagnosis. Read IBM PS/2 Model 70 Capacitor Replacement Guide for the recap procedure.
MCA-Specific Faults
[edit | edit source]165 Card-ID Mismatch
[edit | edit source]The Model 70's three MCA slots make 165 less common than on a Model 80, but the fault mode is identical. Causes:
- Card was added or removed without running Auto Configuration.
- MCA edge contact oxidation.
- RTC battery died and CMOS lost the configuration record (cluster with 161/162/163).
- CMOS battery is fine but the saved configuration was corrupted.
Fix:
- Boot the Reference Diskette.
- Select Set Configuration → Run Auto Configuration.
- Insert option diskettes as prompted.
- Save and reboot.
If 165 persists after Auto Configuration:
- Reseat every MCA card. Clean edge fingers with eraser and contact cleaner.
- Try removing all cards, run Auto Configuration with bare planar, then reinstall cards one at a time.
- Suspect SMD electrolyte leakage on the planar near the MCA bus controller.
Power Platform-Specific Faults (8570-B21 / B61)
[edit | edit source]The Power Platform daughtercard adds its own failure modes:
- Power Platform regulator failure — the on-card +5 V regulator can fail and the daughtercard receives no power. Diagnosis: probe the +5 V test point on the Power Platform.
- Power Platform clock generator failure — the 80486DX receives no clock.
- Power Platform Reference Diskette mismatch — if a standard E61 / 121 / A21 Reference Diskette is booted on a Power Platform-equipped 8570, the 80486-specific BIOS extensions are not loaded and some diagnostics will fail.
- Cache test failure — the Power Platform exposes the 80486 on-die 8 KB cache for testing in Advanced Diagnostics. A cache test failure is a daughtercard fault, not a planar fault.
ECA Recalls and Service Bulletins
[edit | edit source]The Model 70 was affected by several Engineering Change Authorisation (ECA) bulletins:
- ECA 087 — Reference Diskette compatibility update for newer MCA cards.
- ECA 092 — Planar fix for one revision of the Model 70 with an erratic memory timing.
- ECA 117 — ESDI controller firmware update.
These ECAs apply only to specific FRU part numbers; check the planar / card FRU against the bulletin before applying.
PSU Faults
[edit | edit source]Symptoms and diagnosis:
- Dead — no fans, no power: Bulk capacitor or mains rectifier; verify mains; PSU recap required. See IBM PS/2 Model 70 Capacitor Replacement Guide.
- Fans spin briefly, then click-retry: Power Good not asserted in 150 ms. Could be PSU fold-back or shorted planar tantalum / leaked SMD electrolyte.
- Boots cold, fails when warm: Secondary electrolytics aged. Recap.
- Audible whine, smell of fish: RIFA X2 cap is venting.
- Rails low/high: PSU feedback path issue. Recap and retest.
Drive Stiction
[edit | edit source]ESDI drives in the 8570 are prone to spindle stiction after long storage. Same procedure as the Model 60:
- Power off.
- Open the chassis. Locate the drive.
- Gently rotate the drive case 45–90° around its spindle axis in both directions to free the heads.
- Re-install. Power on.
After the drive boots, immediately image its contents to a modern disk image file. The drive cannot be trusted to spin up reliably again.
Floppy Faults
[edit | edit source]Same as Model 60 (see IBM PS/2 Model 60 Troubleshooting Guide).
Keyboard / Mouse Faults
[edit | edit source]- 301: Keyboard or mouse in the wrong port.
- 305: +5 V fuse on planar blown.
- 365: PS/2 mouse fault.
Memory Faults
[edit | edit source]- 201 with address in the on-planar range: SIMM (planar memory) failure. Note: the Model 70 uses IBM proprietary 72-pin SIMMs.
- 201 with address in an MCA memory adapter range: Memory adapter card failure.
- 215 / 216: MCA Memory Adapter configuration error.
When to Suspect the Planar
[edit | edit source]- 1xx errors that persist after CMOS battery replacement and Auto Configuration.
- 10x errors with no other peripheral fault visible.
- No video and no beeps after PSU verified known-good.
- Repeated 165 errors after every card removed and reseated and a full Auto Config done.
- Any visible SMD electrolyte leak.
The single most common Model 70 planar failure is SMD aluminium electrolyte leakage. See IBM PS/2 Model 70 Capacitor Replacement Guide.
Diagnostic Workflow
[edit | edit source]- Visually inspect planar for SMD electrolyte leak first. If found, do not power on.
- Power on. Listen for beep.
- Note POST screen — any leading numeric code.
- If 161/162/163 cluster — replace DS12887 module.
- If 165 — run Auto Configuration.
- If 17xx (n/a — no ST-506 on Model 70) / 104xx — verify drive type in CMOS; reseat drive cable; consider stiction; consider controller cap failure.
- If 24xx — planar VGA fault, often SMD electrolyte leak.
- If 104 — 80386 protected mode fault, often SMD electrolyte leak near CPU.
- If no beep and no video — PSU first (rail check), then planar SMD inspection.
- Run Advanced Diagnostics (Ctrl-A) once basic POST passes.
Related Pages
[edit | edit source]- IBM PS/2 Model 70
- IBM PS/2 Model 70 Maintenance Guide
- IBM PS/2 Model 70 Capacitor Replacement Guide
- IBM PS/2 Model 80 Troubleshooting Guide — tower sibling, same planar family
- IBM PS/2 Model 60 Troubleshooting Guide — predecessor
References
[edit | edit source]- PS/2 Error Codes — Ardent Tool of Capitalism. Source for the 1xx–104xx error code tables.
- IBM PS/2 Model 70 — Ardent Tool Quick Reference. FRU data and ECA history.
- IBM, IBM Personal System/2 Hardware Maintenance Manual (S52G-9971-02, October 1994). POST error code reference.