A 1995 Kern CD650 reported INT 2: NMI/PARITY INTERRUPT! on an 80486 at approximately 0690:2A68, followed by a restart that stopped at the HEIDENHAIN loading screen. Treat the address as approximate because the recorded value is uncertain. The evidence supports checking memory, machine constants, communication paths, and stored data; it does not identify a confirmed root cause.
Separate confirmed symptoms from suspected causes
| Observation | Engineering interpretation |
|---|---|
| Intermittent serious errors during operation | The failure preceded the current startup lockup, so inspect persistent data and hardware paths rather than treating the loading screen as an isolated display issue. |
INT 2: NMI/PARITY INTERRUPT! |
A parity-related failure is confirmed, but the evidence does not prove that the RAM module caused it. |
| Startup now stops at the HEIDENHAIN loading screen | Determine the last completed loading stage before changing configuration or hardware. |
BIOS battery measures 2.7 V; clock and settings remain present |
The measurement alone does not establish that the battery caused the parity interrupt or startup lockup. |
Run the supported diagnostic sequence
- Record the complete error text, the displayed address, and the exact point where loading stops. Confirm whether the approximate address
0690:2A68appears again. - Test the replacement RAM when available. The installed RAM was already removed, cleaned, and reseated without changing the fault, so another compatible module provides a stronger memory test than another reseat.
- Recheck the power rails while the control attempts to boot. Previous oscilloscope checks of the
5 Vand12 Vsupplies showed no large change, but that result does not eliminate RAM, data, or interface faults. - If machine constants are accessible, verify the character-set settings in
MC_0905,MC_0915, andMC_0925. Correct only the relevant constant when its stored setting is known to be wrong. - Inspect communication cabling and interfaces for connection faults, then check the storage-medium contents for corrupted information or inconsistent parity handling.
Protect configuration before battery work
The retained clock and BIOS settings show that configuration is still present at the time of observation. The evidence does not identify which settings could be lost, provide a backup method, or validate a live battery replacement. Do not use a hot-swap procedure based solely on this fault report. First document every accessible setting and obtain the control-specific battery replacement and configuration-retention procedure through an official HEIDENHAIN support channel.
Verify the repair and decide the next action
After changing one item, cold-start the control and verify that it passes the previous loading point, reaches an operational screen, and completes a run without another parity interrupt. If the replacement RAM produces no change, preserve the exact boot-stage observations and machine-constant values for HEIDENHAIN support. Conversion to Manualplus M is mentioned only as a possible backup plan; the evidence provides no supported hardware, software, compatibility, or migration requirements.
FAQ
What does INT 2: NMI/PARITY INTERRUPT on an 80486 mean?
It confirms a parity-related interrupt, but it does not by itself prove defective RAM. The supported checks also include MC_0905, MC_0915, MC_0925, communication interfaces, and stored data.
Should I replace the 2.7 V BIOS battery while the control is powered?
The evidence does not validate a hot swap or identify which settings may be lost. Document the configuration and obtain the control-specific replacement procedure before disturbing the battery.
What should I test if reseating the RAM does not fix the startup lockup?
Test another compatible RAM module, verify the three character-set machine constants, inspect communication cabling and interfaces, and check the storage medium for corrupted or parity-inconsistent data.
