Kodak TH2 Laser Head: LVD Fault Fixed by Re-soldering FPC Connector

Back: Technical Articles Home WhatsApp: +86 136 0182 8454

Kodak TH2 Laser Head: LVD Fault Fixed by Re-soldering FPC Connector

LVD module image

Problem Summary

A Kodak TH2 laser head failed to maintain light balance, producing uneven output and calibration errors. The root cause was not the LVD (Liquid Crystal Light Valve) itself but a desoldered FPC (Flexible Printed Circuit) connector on the LVD module. After re-soldering the connector, the laser head was fully restored.

Field Symptoms

The customer reported the following issues:

  • Light balance calibration could not complete successfully.
  • Uneven exposure in flat-tint areas.
  • Erratic output quality with noticeable fluctuations.
  • Some areas of the plate exhibited abnormal exposure.

Initial checks confirmed laser power was normal and the optical path had no visible contamination. The symptoms pointed to an LVD control anomaly.

Error Meaning

The LVD in the TH2 laser head modulates light transmission for each laser beam to achieve consistent exposure across the scan line. The LVD communicates with the control board via a Flexible Printed Circuit (FPC) cable.

When the FPC connector exhibits:

  • Desoldering (complete separation)
  • Cold solder joints
  • Poor contact
  • Loose connection

Control signals become intermittent or lost, leading to:

  • Light balance failure
  • Inconsistent laser output
  • Uneven flat-tint density
  • Calibration failure

In severe cases, the entire LVD module may appear non-functional.

Diagnostic Path

Instead of immediately replacing the LVD, the diagnostic flow followed:

  1. Verify laser power.
  2. Inspect optical components for contamination.
  3. Examine the LVD drive and control signals.
  4. Check the FPC cable and its connector.
  5. Inspect solder joints for cracks or separation.
  6. Only if all else fails, consider LVD element replacement.

What Was Checked On Site

The laser head was disassembled to access the LVD module. Visual inspection under a microscope revealed that several pins on the LVD FPC connector had completely desoldered from the PCB. The surrounding solder joints showed no cracks, confirming a fatigue failure likely from thermal cycling and mechanical stress.

Repair Action

  1. Remove old solder and clean the PCB pads.
  2. Inspect pad integrity — all pads were intact.
  3. Re-align the FPC connector precisely.
  4. Reflow solder using precision hot air, with controlled temperature and flux.
  5. Inspect all pins under microscope to ensure complete wetting.
  6. Perform continuity checks between FPC lanes and LVD pads.
  7. Reassemble the laser head and install in the CTP.

Final Result

After re-soldering:

  • Light balance calibration passed immediately.
  • LVD operation stabilized.
  • Flat-tint output became uniform.
  • All print tests passed continuous run.

LVD curve before repair (Before repair: LVD characteristic curve showed anomalies)

LVD curve after repair (After repair: LVD curve returned to normal)

The LVD liquid crystal element itself was not damaged. Re-soldering the FPC connector saved the entire LVD module and significantly reduced repair cost.

Engineering Lesson

For Kodak TH2, TH3, TH5, and similar series laser heads, a light balance anomaly should not automatically be attributed to a failed LVD. The following checklist is recommended:

  1. Confirm laser power.
  2. Check optics for contamination.
  3. Inspect LVD drive signals.
  4. Examine FPC cable and connector.
  5. Look for solder defects on the LVD FPC header.
  6. Only then evaluate the LVD element.

Field experience shows that FPC connector solder failures account for a significant portion of LVD-related issues. Correctly diagnosing a connection fault reduces downtime and avoids unnecessary part replacement.

Related Services

DTP TECH provides specialized repair and support for Kodak CTP laser heads, including:

  • TH1 / TH2 / TH3 / TH5 / TH6 / TH7 laser head repair
  • LVD inspection and rework
  • Precision soldering of FPC cables and connectors
  • Laser optical path alignment
  • Light balance calibration
  • Laser power measurement and lifetime assessment
  • Remote CTP troubleshooting

CTA

Are you facing light balance issues on your Kodak CTP? Could a simple solder joint be the hidden cause? Share your experience or contact us for diagnostic support.

Contact Us