Samsung CLX-8640 series Service Manual page 272

4. Troubleshooting
5) Remove the rear cover after removing 7 screws.
6) Measure the resistance value of two connectors(CN37_12 / CN37_13) at both ends.
7) If the value is not in 47.5KΩ ~ 52.5KΩ (@25 ℃), replace the harness(JC39-01733A).
8) If the harness and sensor are normal, replace the main board(JC92–02516A)
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