Koyo DirectLOGIC DL05/DL06 — CPU Errors & Battery

Koyo · beginner · 20 min

A Koyo DirectLOGIC DL05/DL06 that drops out of Run, blinks its CPU light, or won't power up is telling you exactly what's wrong through its indicators and special relays. Learn the PWR/RUN/CPU LEDs, the fatal-error behavior, and the battery and RAM-checksum flags.

ℹ️ On a DL05/DL06, a fatal error forces the CPU from Run into Program mode and won't let you go back to Run until it's fixed. The special relays SP43 (battery low) and SP44 (RAM checksum) and the V-memory error registers tell you which fault you have.

Read the CPU indicators

The Koyo DirectLOGIC DL05/DL06 (sold by AutomationDirect) shows its health on the front-panel LEDs:

• PWR — power supply good. At power-up the PWR indicator must be on; if it isn't, remove power and check all wiring (input power, fusing) per the maintenance/troubleshooting chapter before anything else.
• RUN — the CPU is in Run mode and scanning.
• CPU — a CPU error/fault. A blinking CPU light is a specific signal (see battery, below).

Fatal errors force Program mode

Fatal errors are faults that could make the system behave improperly (a potential safety problem). When one occurs, the CPU automatically switches to Program mode if it was running — and if it's already in Program mode it won't let you transition to Run until the error is corrected. So "it won't go into Run" is usually an uncorrected fatal error, not a mode-switch problem.

A first, cheap step for many transient errors: you may be able to clear the error by power-cycling the CPU. If a write to the DL06 wasn't successful, power-cycle; if the error returns, the unit needs replacing.

Battery-low: SP43 and a blinking CPU light

When the lithium backup battery is low, the CPU tells you three ways at once:

• Special relay SP43 turns on.
• The error code is stored in V7757.
• The CPU indicator blinks when the battery is below 2.5 VDC.

Replace the battery (with the program safely stored) to clear it.

RAM-checksum: SP44 and V7755

A checksum error in system RAM sets special relay SP44 on and stores the code in V7755. Likely causes are a low battery, electrical noise, or a CPU RAM failure. The fix: clear the memory and download the program again, and correct any grounding problems — a poorly grounded panel injecting noise is a classic cause of intermittent checksum faults.

Step-by-step

1. PWR off? Kill power, check input wiring/fuse before anything else.
2. Won't enter Run / dropped to Program? You have an uncorrected fatal error — read the error code (Appendix B of the DL06 manual lists the full set).
3. CPU light blinking / SP43 on? Battery low (< 2.5 VDC) — replace the battery.
4. SP44 on / code in V7755? RAM checksum — clear memory, re-download the program, and fix grounding/noise.
5. Transient error? Power-cycle to try to clear; if it returns, replace the unit.

Never do this

Don't paper over a repeating RAM-checksum or fatal error by just clearing it every shift — it usually means real electrical noise/grounding trouble or failing hardware. Fix the grounding or replace the unit so the machine isn't running on a CPU that can fault unpredictably.