IBM PS/2 Model 25 Troubleshooting Guide

This guide covers diagnostic procedures and the complete IBM PS/2 numeric POST error code reference applicable to the Model 25 (8525). The PS/2 BIOS uses a "Major Error Code / Minor Diagnostic Error Code" structure that is mostly identical to the PC/AT 1xx–19xx codes but extends them with many PS/2-specific minor codes. Codes specific to MCA hardware (which the Model 25 does not have) are excluded. SCSI- and Pageprinter-specific codes are not listed.

Audio Beep Codes

The Model 25 BIOS uses the standard PS/2 audio beep code scheme. Beep codes are produced by the PC speaker (also routed through the earphone jack on the rear) before video has initialised.

IBM PS/2 power-on audio codes

Pattern	Meaning
1 short beep (*)	POST OK, system boot normal
2 short beeps (**)	Problem found; check configuration. Run Advanced Diagnostics if no error code displayed
1 long + 1 short (_ *)	Display or display adapter problem (MCGA / VGA)
1 long + 2 short (_ * *)	Display or display adapter problem (VGA)
1 long + 3 short (_ * * *)	EGA / display adapter problem
Continuous short beeps (* * * * * * *)	Keyboard problem — check fuse F1, keyboard cable, 8042 controller
Continuous solid beep (____________)	System board failure
Click followed by no beep	Power-good signal absent — PSU started but planar did not assert Power Good in 150 ms. Suspect a shorted tantalum on the planar.
No display and no sound	Power problem — check mains and PSU. PSU may be in fold-back protection due to a shorted tantalum on the planar, an improperly seated SIMM, a defective adapter card, or a stuck power switch

If the audio pattern is "1 long + 1 short high beep" with the system halted, the BIOS has detected the CPU running at a clock speed outside its expected window. This is unusual on a Model 25 unless the 48 MHz oscillator has drifted.

Numeric POST Error Codes

The PS/2 error code is in the format MMMMM NN (or the 4 + 4 extended format on Premium Line LED panels). The MMMMM major error is essentially the PC/AT code; the NN minor code is supplied by Advanced Diagnostics and provides additional detail. Where the minor code is not displayed (as is normal during POST), only the major code appears. The following sections list the major codes applicable to the Model 25.

1xx — System Board

Major code 1xx — system board

Code	Meaning
101	Main system board failed — processor or 8259 PIC interrupt failure
102	Timer failure (8253 PIT channel 0) or BIOS ROM checksum error. Try reseating the U13/U17 (U19/U20) BIOS ROMs
103	Timer interrupt failure or 2 KB CMOS RAM test failure (Model 25 286 / SX only)
104	8259A interrupt controller error or 80286 protected-mode failure (Model 25 286 / SX)
105	Last 8042 keyboard controller command not accepted
106	Converting logic test — planar
107	NMI test failure (parity check) — planar
108	PC/AT-class memory error or memory too slow for the CPU; on PS/2, timer bus test failure (8253/8254)
109	DMA (8237A) test error
110	Planar parity error
111	I/O parity error (adapter card memory) or 80286 protected-mode test
112	Watchdog timeout (adapter failure)
113	DMA arbitration timeout (adapter failure)
114	External ROM checksum error
115	80386 protected mode test (Model 25 SX)
121	Unexpected hardware interrupt
131	Cassette wrap test failed (legacy code from the 5150 lineage)
151	Bad battery (Model 25 286 / SX RTC battery)
152	Real-time clock or CMOS error (battery low or power-on password installed)
160	Planar ID not recognised — commonly caused by a loose I/O channel riser card
161	System options not set — run SETUP from the Reference Diskette
162	System options not set / CMOS checksum mismatch — run SETUP
163	Time and date not set / RTC not updating
164	Memory size error — CMOS does not match installed RAM. Run SETUP
165	System options not set — card ID mismatch
166	Card busy error (adapter failure)
167	Clock not updating (Model 25 286 / SX)
171	I/O Card Failure or battery (PCC)
172	Static RAM failure
173	RTC RAM verification error
181	Unknown adapter
199	User-indicated configuration not correct

161 / 162 / 163 cluster

This cluster typically indicates a dead RTC battery on the Model 25 286 or Model 25 SX. The Dallas DS1287 / DS12887 / Odin module's internal lithium cell has run down and CMOS contents are lost. Replace per IBM PS/2 Model 25 Maintenance Guide and re-run SETUP.

Note that on the Model 25 SX, a 161/163 condition also defaults the floppy drive to 720 KB only regardless of the diskette inserted. After replacing the battery and running SETUP, 1.44 MB media is readable again.

2xx — Memory

Major code 2xx — memory

Code	Meaning
201	Memory test failed — data miscompare, parity error, or bad adapter. The hex digits preceding "201" identify the failing 64 KB bank and the failing bit:
	0yzz = 1st 64K bank (000–064K) ... 9yzz = 10th 64K bank (576–640K)
	zz = bad data bit: xy00 parity, xy01 bit 0, xy02 bit 1, xy04 bit 2, xy08 bit 3, xy10 bit 4, xy20 bit 5, xy40 bit 6, xy80 bit 7
202	Memory address line failure (address lines 0–15)
203	Memory address line failure (address lines 16–23) or refresh failure
204	Relocated memory — run diagnostics again
205	CMOS error
207	ROM failure
211	Base 64K on I/O channel failed — put memory into machine
215	Base 64K on daughter card 2 failed (card possibly in wrong slot)
216	Base 64K on daughter card 1 failed (card possibly in wrong slot)
221	ROM-to-RAM mapping error. Latches until the memory is fixed and SETUP rerun
225	Memory may be wrong type, defective, or not fast enough

Decoding 201 errors

On a Model 25 8086 with 640 KB installed, a "5810 201" error decodes as follows:

• 5: 6th 64K bank (320–384K).
• 8: Don't care on Model 25 (this digit identifies a 16K sub-bank on 5150 PC-I motherboards only).
• 10: Data bit 4 (the fifth chip after the parity chip in that bank).

For the Model 25 8086 planar, banks 0–3 are on-board at U16/U33/U34/U35 plus U44/ZM1, and bank 4+ is on the optional 128 KB memory module. Failures in bank 0 (POST cannot complete) cause a continuous beep; failures in higher banks display 201 with the bank/bit pattern.

3xx — Keyboard

Major code 3xx — keyboard

Code	Meaning
301	Keyboard did not respond / stuck key. The hex value preceding "301" is the scan code of the stuck key (e.g. "5C 301" = stuck "\" key). On the Model 25, a 301 also occurs if the keyboard is plugged into the mouse port or vice versa
302	User-indicated keyboard test failure
303	Keyboard or planar (8042) error
304	Planar (8042) error / CMOS does not match keyboard
305	Keyboard +5 V fuse failure. Replace fuse F1 on the planar (3 A). On the Model 25 286 (8525-006), a 305 with no beep and no fall-through to the F1 prompt is the symptom of ECA 082 — planar replacement under IBM Engineering Change Authorization

Stuck-key 301 errors and the DASDDRVR.SYS workaround

If a Model 25 reports a XX 301 error at POST and XX is a hex scan code, an object resting on a keyboard key is the most likely cause. If multiple keys appear stuck, the system also reports 8602 (user-indicated pointing device error).

A 301 error that only occurs on a warm boot (Ctrl-Alt-Del) within ~1 minute of a previous power-on is a known IBM-documented issue addressed by installing DASDDRVR.SYS (a device driver on the Reference Diskette version 1.02 and higher). To install:

1. Boot DOS from a working diskette.
2. Insert the Reference Diskette in drive A:.
3. Type "A:INSTALL" and follow the prompts.
4. DASDDRVR.SYS is required for DOS 3.3 and DOS 4.0 on the Model 25.

305 ECA 082

Model 25 286 (8525-006) systems with a serial number in a specific range exhibit a "305 error at POST, no beep, no F1 fall-through" symptom. IBM issued Engineering Change Authorization 082 for replacement of the planar. The affected machines do not respond to F1 to bypass the error, so the system cannot be booted; the only fix is planar replacement.

4xx — Monochrome Display Adapter / MCGA

Major code 4xx — display (monochrome paths)

Code	Meaning
401	Monochrome memory test, horizontal sync, or video test failed. On the PS/2 Model 25, this code is also raised by the planar MCGA CRT error path
408	User-indicated display attribute failure
416	User-indicated character set failure
424	User-indicated 80×25 mode failure
432	Parallel port wrap test failed on the monochrome adapter (legacy code; the Model 25 parallel port may instead raise 9xx)

5xx — Colour Graphics / MCGA / VGA

Major code 5xx — display (colour paths)

Code	Meaning
501	Colour memory test, horizontal sync, or video test failed. On the PS/2 Model 25, the planar MCGA / VGA CRT error path. Run Advanced Diagnostics and observe the minor code
508	User-indicated display attribute failure
516	User-indicated character set failure
524	User-indicated 80×25 mode failure
532	User-indicated 40×25 mode failure
540	User-indicated 320×200 graphics mode failure
548	User-indicated 640×200 graphics mode failure

6xx — Diskette Drive / Controller

Major code 6xx — diskette drive

Code	Meaning
601	Diskette power-on diagnostic test failed (drive or controller)
602	Boot record on diskette invalid
606	Diskette verify function failed
607	Diskette is write-protected
608	Bad command (status from NEC controller)
610	Diskette initialisation failed
611	Timeout — controller did not respond
612	Bad NEC — diskette controller (uPD765 / D765BC) returned a fault
613	Bad DMA — diskette DMA channel failed
621	Bad seek
622	Bad CRC
623	Record not found
624	Bad address mark
625	Bad NEC seek
626	Diskette data compare error
630–633	Index or track-0 signal stuck on drive A (PS/2 specific)
640–643	Index or track-0 signal stuck on drive B
650	Drive speed error
651	Format failure
652	Verify failure
653	Read failure
654	Write failure
655	Controller error
656	Drive failure
657–660	Write-protect or change-line signal stuck

For a Model 25 with a single floppy bay, 640–643 indicate a problem with the second drive cable / connector even if no drive is fitted. Inspect the PS/2 single-cable connector at the planar.

7xx — Math Coprocessor

Major code 7xx — math coprocessor

Code	Meaning
7xx	8087 (Model 25), 80287 (Model 25 286), or 80387SX (Model 25 SX) math coprocessor error
702	Exception errors test (80387 / 80287)
703	Rounding test
704–707	Arithmetic tests 1–3 and combination test
708	Integer / store test
709	Equivalent expressions test
710	Exceptions (interrupts)
711	Save state (FSAVE)
712	Protected mode test
713	Special test (voltage / temperature sensitive)

9xx and 10xx — Parallel Port

Major codes 9xx / 10xx — parallel port

Code	Meaning
901	Data register latch error
902	Control register latch error
903	Register address decode error
904	Address decode error
910	Status line(s) wrap connector error
911–915	Status line bit-N wrap error
916	Interrupt wrap failed
917	Unexpected printer adapter interrupt
92x	Feature register error
10xx	Parallel printer adapter (alternate port)

11xx and 12xx — Serial Port

Major code 11xx — primary serial port

Code	Meaning
1101	8250 / 16450 / 16550 ASYNC chip error
1102	Card selected feedback error
1103	Port 102h register test failure
1106	Cannot put serial option to sleep
1107	Cable error
1108 / 1109	IRQ3 / IRQ4 error
1110–1119	Various UART internal tests (transmit, receive, modem control, baud-rate, FIFO)

Codes 12xx are the same set for an alternate (second) serial port (Dual ASYNC).

13xx — Game Port and 14xx — Printer

• 1301 / 1302 — Game adapter / joystick test failure.
• 1401 — Printer failure.
• 1402 — Printer not ready / out of paper.
• 1403 — Printer no paper / interrupt failure.
• 1404 — System board timeout for printer.
• 1405 — Parallel adapter failure.
• 1406 — Presence test failed.

17xx — Fixed Disk

Major code 17xx — fixed disk

Code	Meaning
1701	Presence code — controller POST error
1702	Timeout
1703	Seek failure
1704	Controller error
1705	Record not found
1706	Write failure
1707	Bad track 0
1708	Bad reset / head select
1709	ECC error or Disk 0 error
1710	Drive not ready / read buffer overrun
1711–1740	Various ECC / addressing / format / sense / data-compare faults
1750	Drive X verify failure
1751	Drive X read failure
1752	Drive X write failure
1753	Drive X random read test error
1754	Drive X seek test error
1755	Controller failure
1756	Controller ECC test failure
1757	Controller head-select failure
1780 / 1781	Timeout for hard disk drive 0 / drive 1 at IPL — drive not up to speed, missing format, control cable problem
1782	Fixed disk controller error
1790 / 1791	Fixed disk drive 0 / 1 error — no drive, data cable off, or format not recognised

On the Model 25 286 with the 30 MB ST-506 drive, 1780 with the drive present is most commonly drive stiction; with the system powered off, gently rotate the drive case to free the heads, then re-power. Replace the drive at the earliest opportunity.

18xx — I/O Expansion / Adapter Card Bus

• 1801 — I/O Expansion unit POST error.
• 1810–1821 — Extender / receiver card faults.

The Model 25 has only two ISA slots (three on the 25 SX), but an 18xx error is reported when a bus adapter card has been installed and fails initialisation.

24xx — Enhanced / VGA Adapter

• 2401 — PS/2 planar video error. On the Model 25 8086 this code is raised by an MCGA failure; on the 286 / SX it is raised by a VGA failure. If DOS text appears in unexpected colours, the planar VGA gate array is suspect.
• 2402 — Diagnostic video error.
• 2408 — VGA ground circuit fault.

A 2401/2402 raised by version 1.00 of an early Reference Diskette on an 8512 display is a known false error; upgrade to Reference Diskette 1.02 or later.

86xx — Pointing Device (Mouse)

• 8601 — System board or pointing-device error.
• 8602 — User-indicated pointing-device test failure. If a 301 also appears, see the 301 keyboard section.
• 8603 — System board (8042) or pointing-device error.
• 8604 — System board or pointing-device error.

A keyboard plugged into the pointing-device port (or vice versa) on the Model 25 produces a 301 (keyboard) and possibly an 8603 (pointing device). Switch the cables and re-run POST.

Reference Diskette and Advanced Diagnostics

The Model 25 has no built-in SETUP screen. All setup and diagnostics are performed by booting the IBM Personal System/2 Reference Diskette that ships with the machine. Important behaviours:

• Always cold-boot the Reference Diskette — insert it before powering on. Warm-booting (Ctrl-Alt-Del with the diskette in the drive) may cause false errors and may falsely indicate a power-on password is already set.
• From the main menu, press Ctrl-A to enter Advanced Diagnostics. Advanced Diagnostics produces minor (NN) codes that further identify the failing FRU.
• If multiple POST errors are reported, resolve them in the order presented — the first fault often causes the others.
• The Reference Diskette is model-specific. A Model 30 Reference Diskette is not interchangeable with the Model 25 Reference Diskette. Use the diskette image specific to your machine type 8525 generation.

A Model 25 Reference Diskette image (machine-type 8525) is available from the Walsh Computer Technology PS/2 archive and from the Ardent Tool of Capitalism. Burn the image to a DSDD 720 KB diskette (or 1.44 MB for the 286 / SX).

Dead System — Isolation Procedure

When the Model 25 shows no signs of life (no display, no beeps, no fan, or fan only without POST), the most likely cause is a device shorting one of the PSU rails. Per IBM, the planar must present "Power Good" within 150 ms or the PSU shuts down internally to protect itself.

Procedure:

1. Verify mains power: check the wall outlet and the chassis power switch. Intermittent dead-system symptoms are often caused by a loose mains lead at the IEC connector; reseat or replace.
2. Disconnect all external connections (keyboard, mouse, monitor pass-through on the 286 / SX, serial, parallel).
3. Open the chassis (after CRT + PSU discharge, see IBM PS/2 Model 25 Maintenance Guide).
4. Remove all ISA cards, all SIMMs (Model 25 286 / 25 SX), and the optional hard drive.
5. Power on and listen for a beep.
6. If no beep: verify continuity through the speaker (the PC speaker is mounted near the front of the chassis). If continuity is good, suspect planar memory (Model 25 8086: bank 0 at U16/U33/U34/U35; Model 25 286: J9 SIMM). Replace planar memory and retry.
7. If still no beep: verify PSU voltages on the planar power connector with a multimeter (see IBM PS/2 Model 25 Maintenance Guide). If voltages are out of tolerance, replace the PSU. If voltages are in tolerance with the planar dead, suspect the planar itself.
8. If beep occurs: re-add SIMMs / ISA cards one at a time. When the beep stops on a given card, that card is faulty or wrongly seated.

A known "dufus" trick (per Louis Ohland's PS/2 documentation): a SIMM inserted backwards has been observed in service. With enough force, anything is possible. Inspect SIMM polarity before suspecting the planar.

Common Symptoms

Continuous beep at power-on, no display

• Most common cause: shorted tantalum on the planar pulling +5 V or +12 V down. The PSU detects the short and folds back; the speaker may emit a continuous click or low tone from residual ripple. See IBM PS/2 Model 25 Capacitor Replacement Guide.
• Less common cause: keyboard fuse F1 (3 A) blown. Symptom: continuous beeping at power-on, system does not POST. Replace fuse.

System POSTs, but display is black

• Verify the CRT is on (some Model 25 chassis have a small intensity dial).
• Verify the integrated VGA / MCGA cable from the planar to the CRT is seated.
• On the Model 25 286 / SX, verify no external VGA monitor is connected to the rear VGA pass-through (this disables the internal CRT on some early submodels).
• If the planar generates VGA at the rear connector but the integrated CRT is dark, suspect the CRT yoke flyback, the EHT transformer or the integrated video amplifier.

"Insert system diskette" message at every boot

• The Model 25 has no ROM BASIC; if no boot diskette is found, the BIOS prompts for a system diskette. This is normal and not an error.
• If a hard drive is fitted and configured in CMOS but the system still asks for a system diskette, suspect a boot sector problem (run FDISK from DOS / Reference Diskette to verify the partition table).

161 / 163 errors at every boot

• Battery on the Model 25 286 / 25 SX. See IBM PS/2 Model 25 Maintenance Guide for the DS12887+ replacement procedure.
• On the Model 25 SX, the symptom also includes the floppy reverting to 720 KB only.

96 8N1 ASCII console code (Model 25 SX)

The "96 8N1" message indicates a serious CMOS / RTC fault on PS/2 systems. Per IBM HMM Oct 1994, the recommended fix is to "Replace the battery and restart the system." Empirical evidence per Peter Wendt: isolate the battery and toggle the startup password jumper simultaneously. There appears to be planar logic that ANDs the two conditions on a power-on and clears the entire CMOS only when both are present. Moving only the jumper or only isolating the battery typically does not clear the condition.

System resets randomly under load

• Most likely cause: aged PSU electrolytic capacitors. Symptom is more pronounced under load (CRT warm-up + drive spin-up + ISA card current draw).
• Verify all rails at the planar with a multimeter, then with an oscilloscope if available, while the system is under load.
• Consider a PSU recap (see IBM PS/2 Model 25 Capacitor Replacement Guide) or a PSU swap with a tested unit.

Floppy drive symptoms

• 601 at POST, drive does not seek: suspect drive, drive logic-board capacitors, or PS/2 single-cable connector. Reseat the cable. Try a known-good Sony PS/2 drive in the same bay.
• 601 at POST, drive seeks but cannot read: suspect dirty heads or aged drive logic-board electrolytics. Run a head-cleaning diskette; if that fails, recap the drive logic board.
• 650 drive speed error: belt on Mitsubishi MF355C / F drives is stretched. Replace belt.
• 651 format failure: drive will not format new media. Suspect drive or media compatibility. Verify the diskette is DSDD for a 720 KB drive or DSHD for a 1.44 MB drive.

Hard drive symptoms (Model 25 286 with ST-506)

• 1701 / 1780 with the drive present: drive stiction. Gently rotate the drive while powered off, then re-power. Replace the drive at the earliest opportunity — this is a sign of imminent failure.
• Drive spins up but no detect: verify CMOS drive type matches the drive (often type 5 or type 17 for 30 MB ST-506).

Power-On Password and Password Override

The Model 25 supports a power-on password stored in CMOS (Model 25 286 / SX only). The password is set from the Reference Diskette. If the password is lost, the only IBM-supported recovery is the password-override connector on the planar (J13 on the Model 25 286). Place a jumper on J13 momentarily during power-on; the BIOS detects the override and clears the password from CMOS. On the Model 25 SX, the equivalent is J2.

Related Pages

• IBM PS/2 Model 25
• IBM PS/2 Model 25 Maintenance Guide
• IBM PS/2 Model 25 Capacitor Replacement Guide
• IBM PC AT Troubleshooting Guide

References

• PS/2 Error Codes, Ardent Tool of Capitalism. Reference for the 4 + 4 Major / Minor code format, dead-system isolation procedure, multiple POST error procedure, and the 96 8N1 / password jumper recovery.
• PS/2 Error Codes, Museodelcomputer.org. Reference for the complete 1xx–25xx PS/2 error code list and the PCC / PCAT distinctions.
• IBM, IBM Personal System/2 Hardware Maintenance Manual (October 1994, document S30G-2207). Source for ECA 082 (305-no-beep planar replacement) and the 96 8N1 clear procedure.
• IBM, IBM Personal System/2 Model 25 Reference Diskette (machine-specific). Source for SETUP, Advanced Diagnostics (Ctrl-A), DASDDRVR.SYS, and the 301-stuck-key workaround.
• IBM PS/2 Model 25 — DOS Days. Reference for the planar IC layout and the 161/163 floppy-defaults-to-720KB Model 25 SX symptom.