BOSS 5 Code 704007: CPU Stall, Not Proof of XDI Failure

BOSS 5 code 704007 stays on the display and will not reset. You may also see the RUN, GOTO, and HOLD LEDs lit. Start with the processor and its power path. A working display proves that the XDI-to-pendant display path is active; it does not prove that the LSI-11 processor is executing.

Stop trying fixes that do not isolate the fault

Several common actions can leave this symptom unchanged. Treat each result as diagnostic information.

• Repeatedly pressing reset: The reset switch cannot recover a processor with missing logic power, poor board contact, cooling trouble, or a hardware failure. Try it once using the correct startup sequence, then test the processor path.
• Removing the LSI-11 and powering up: An unchanged display does not clear the processor. The XDI card interfaces with the pendant display card, so the display can retain or present a code while the processor is absent.
• Removing other logic cards: Leaving only the XDI card confirms little beyond the display interface. It does not demonstrate that the XDI generated the original fault.
• Cleaning without measuring afterward: Electronic cleaner may remove contamination, but it does not prove low-resistance edge-connector contact or correct logic voltage under operation.
• Adjusting the supply immediately: Do not turn the multiturn potentiometers merely because the machine will not boot. Measure the rails at the logic-card terminal strip first and compare them with the required values.

Read the panel symptoms as a processor stall

The closely related code 70007 has repeatedly indicated an LSI-11 that is not functioning. The displayed value here is 704007, so first record every digit exactly and check whether the display is adding a digit, combining fields, or presenting a distinct code. Do not silently treat the two numbers as identical.

Check cooling, seating, and logic power first

Loss of processor execution can come from heat, connector resistance, or a marginal supply even when the display remains alive. Perform these checks before replacing the XDI.

1. Remove power and follow the machine's electrical isolation procedure.
2. Check every cabinet fan. Pay particular attention to the fan beneath the logic boards. Restore airflow before repeating a powered test.
3. Record each board position before removal. Inspect the LSI-11 and the other logic boards for contamination, damaged contacts, or connectors that are not fully seated.
4. Clean edge contacts only with a method suitable for electronic contacts. The documented field method used a soft pink eraser. Remove all residue, avoid abrasive damage, and reseat every board firmly.
5. Restore power and measure the logic rails at the terminal strip immediately to the right of the logic cards. Use the adjacent small light-blue and lavender wires identified for the 5 VDC measurement.
6. Move outward by one wire in each direction for the 12 VDC measurement. The two outside wires identify the -12 VDC rail.
7. Verify polarity, meter reference, and terminal identification before probing. Record the readings during the failed boot, not only with the logic boards disconnected.

The small board in the white logic supply contains labeled multiturn adjustment potentiometers. Adjust a rail only after confirming the correct measurement points and the target from the machine's service data. A no-load reading does not prove that the rail remains correct with the processor installed.

Restore the intended reset and boot sequence

Most BOSS machines may appear to boot by applying power alone, but that behavior is not a dependable startup test. Use the reset switch in the tape-reader cabinet.

1. Install the LSI-11 and all required logic cards in their recorded positions.
2. Confirm that each connector is fully engaged and that the fan beneath the logic boards runs.
3. Apply power while watching the display and logic LEDs.
4. Operate the reset switch in the tape-reader cabinet once.
5. Watch for the displayed code to clear and for the LED states to advance instead of remaining frozen.
6. If the code remains, recheck the logic rails during reset. A rail that changes materially when reset is applied points back to the supply, its wiring, a connector, or an excessive board load.

If power, airflow, and seating are correct but the same state persists, test the LSI-11 before the XDI. Substitute only a known-compatible, verified board; the evidence identifies no exact replacement part number or board revision.

Separate an LSI-11 fault from an XDI fault

Use functional boundaries. The LSI-11 runs the processor logic. The XDI interfaces with the display card in the pendant. A static but readable display therefore places the XDI/display path among the components still producing an output.

• If reseating the LSI-11 changes the boot behavior, concentrate on its edge connector, supply loading, and processor board.
• If a verified LSI-11 boots in the same rack, remove the original LSI-11 from service for bench diagnosis or repair.
• If the display becomes corrupt, blank, or loses communication while processor activity is otherwise present, move the XDI and pendant display path higher in the diagnostic order.
• If the ERR LED lights, inspect the ERS board path instead of interpreting the frozen operating LEDs alone.

Do not use the unchanged code after removing cards as a card-by-card isolation test. A controller without its processor cannot execute the normal code-clearing or boot sequence.

Verify the repair under operating load

1. Cold-start the controller with all required cards installed.
2. Use the tape-reader-cabinet reset switch and confirm that 704007 clears.
3. Confirm that the RUN, GOTO, and HOLD LEDs no longer remain frozen in the original pattern.
4. Measure the 5 VDC, 12 VDC, and -12 VDC rails while the controller is operating.
5. Verify that all fans continue running and that the failure does not return as the logic compartment warms.
6. Repeat the normal power-up and reset sequence. A single successful boot after moving a board is not enough to distinguish a repaired contact from an intermittent one.

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