Troubleshooting “Unexpected Reply” / Error 104 on HP 6890 GC with Chromperfect

Introduction

Occasionally, Chromperfect users working with an HP/Agilent 6890 GC may encounter an error message similar to:

“unexpected reply from GC HTCCID HP 6890 GC REV A.03.08 unit 6 error 104”

The exact wording may vary slightly depending on firmware revision, but the meaning is consistent:

Chromperfect attempted to communicate with the GC and received an invalid or unexpected response.

This is a communication-level issue — not a data processing fault. It is also referred to as "HP 6890 unexpected reply error."

What This Error Actually Means; HP 6890 unexpected reply error 104

Chromperfect communicates with the HP 6890 using a digital serial protocol (HTCCID).

Error 104 indicates that:

• The GC did not reply in the expected format, or

• The GC was not in a valid state to reply, or

• The communication signal was corrupted or interrupted.

In most cases, this is not a software failure. It is a hardware state or connection issue.

Common Causes

This error can occur when:

• The GC is still initializing or in a locked internal state

• The autosampler controller is interfering with serial communications

• Devices are powered on in the wrong order

• Serial cables are loose or partially disconnected

• There is electrical noise or handshake instability on the serial line

• Older firmware revisions behave differently during boot

  
  

Recommended Resolution Procedure

Step 1 — Controlled Power Reset (Correct Order)

I

f this error appears, perform a full shutdown sequence:

1. Power OFF the autosampler (if connected)

2. Power OFF the GC

3. Shut down the PC

Wait at least 30 seconds before restarting.

Then restart in this exact order:

1. Power ON the autosampler first

2. Allow it to fully initialize

3. Power ON the GC

4. Allow it to complete its boot cycle

5. Start the PC last

6. Launch Chromperfect only after Windows is fully loaded

Why This Matters

This order ensures:

• The autosampler does not claim the serial port before the GC

• The GC communication controller is fully initialized

• Chromperfect connects only after both devices are ready

In many cases, this resolves the issue completely.

Step 2 — Check Physical Serial Connections (If Reset Fails)

If the power reset does not resolve the problem, the next most common cause is a physical communication issue.

Perform the following:

1. Power OFF:

   • Autosampler

   • GC

   • PC

2. Physically disconnect:

   • The serial cable between the GC and PC

   • The serial cable between the GC and autosampler controller

3. Inspect:

   • Bent pins

   • Loose connectors

   • Worn or stressed cable ends

   • Poorly tightened thumb screws

4. Firmly reconnect all serial connections.

5. Perform the full restart sequence again:

   • Autosampler → GC → PC

Even a slightly loose serial connector can cause corrupted or malformed responses that trigger this error.

When to Investigate Further

If the issue continues:

• Confirm the correct COM port is configured in Chromperfect

• Check that no other software is accessing the serial port

• Verify firmware revision on the GC

• Test with a known-good serial cable if possible

Persistent issues may indicate:

• Failing serial hardware

• Controller board instability

• Autosampler communication conflict

Final Note

Error 104 and similar “unexpected reply” messages are typically communication-state problems rather than software defects.

In most laboratories, a clean shutdown, correct restart order, and verification of serial connections resolve the issue.