juki kp620 bad response to the hello_cmd

This juki has 2 parts to its system, a PC module which can be a 386/486/Pentium processor board. The software can be DOS or Windows 3.1 IIRC, this PC controller interfaces to a VME 68000 controller that runs all the mechanics and internal interfacing to the machines mechanics via an RS485 ARCNet comms Buss.

This is a ChatGPT repair guide, which is written without a detailed understanding as it has no access to the service manuals, circuits etc it should start you on the ight track

Short version: those messages almost certainly mean the controller is trying to handshake with a subordinate board (or device) during power-up and isn't getting the reply it expects. "HELLO_CMD" is the initial "are you alive / what's your ID+version?" poll; "RESET_CMD" is the follow-on reset/ack step. If either reply is missing or malformed, you see those errors.

I couldn't find an official KP-620E manual with those exact strings, but there's a (very recent) SMTnet thread quoting the same two messages verbatim for a KP-620E, which confirms they're startup handshake/comm failures. JUKI's electronics service channel is the best path for model-specific docs. ([smtnet.com][1])

Here's a practical, step-by-step way to run it down on an older KP-series machine:

1. Identify the failing module • Watch the boot sequence and note what the UI is trying to init just before the error (e.g., head/gantry control, I/O backplane, feeder/vision controller). • If there's a service/diagnostic screen, look for a board address or module name logged with the error. (Often "HELLO" is sent per board).

2. Basics: power and grounds • Measure all rails at the suspect board connector(s): +24 V (if used), +12 V, +5 V, and any logic rails. Ripple >~100 mV on logic rails can break comms. • Inspect and reseat edge and ribbon connectors; clean oxidised contacts; verify chassis ground and shield continuity.

3. Comms layer sanity check • Trace the cable from the CPU/HMI to the module: many of these use RS-422/485-class differential links or a simple serial bus. • With a scope or logic analyser, confirm you see TX activity from the controller right when HELLO should be sent, and that RX toggles in response. No RX == wiring/terminator/receiver issue; garbled RX == noise/baud mismatch/grounding. • Check for missing line termination on differential links and for crushed/abused cable runs through hinges or cable chains.

4. Module status & firmware • Look for status LEDs on the target board (PWR/ERR/RUN/COMM). A steady ERR or no RUN after power-up points to local firmware not booting. • If boards were swapped, verify firmware compatibility: a version mismatch can make the controller reject the HELLO/RESET reply (wrong packet format or ID). • Power-cycle the *module only* (if connectors allow) after the main CPU is up; sometimes a late power-up lets you catch a valid HELLO.

5. Isolation tests • Remove non-essential peripherals (e.g., feeders, aux I/O) and bring the machine up with just the core axis/IO boards. Add modules back one at a time to see which addition triggers HELLO/RESET failures. • If you have a spare of the suspect board, swap it in to determine whether the fault follows the board or stays with the cable/backplane slot.

6. Controller side checks • Backup parameters; then reload controller firmware/parameters if you have the service media. Corrupted NVRAM/params can cause the CPU to expect the wrong device signature. • Check CMOS/RTC backup battery on the CPU/HMI board--dead NVRAM can scramble stored comm configs.

7. When you contact JUKI • Give them the exact text of both messages, the boot step where they appear, and any board designators/LED states you can read. • Ask specifically for the KP-620E controller/service manual pages that define the inter-board protocol (the "HELLO/RESET" handshake) and the board address map. JUKI's electronics assembly support portal is the starting point. ([JUKI Americas][2])

Reference hit with the exact strings (community post): good for confirming you're chasing the right class of problem, though it doesn't include the fix. ([smtnet.com][1])

If you can share: the exact point in the boot flow when the errors pop, which LEDs are lit on the motion/IO/feeder/vision boards, and what comms wiring you see (part numbers/photos help), I can tailor the checks to the right module and suggest pin-by-pin measurements and a minimal-wiring bring-up order.

[1]: https://smtnet.com/Forums/index.cfm?Thread_ID=24858&fuseaction=view_thread&utm_source=chatgpt.com "juki kp620 bad response to the hello_cmd - smtnet.com" [2]: https://jukiamericas.com/pages/technical_support?utm_source=chatgpt.com "JUKI Americas Technical Support"

sarason

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