Make sure used only Calibrated test board from Cal-Tech, Uncalibrated Assembly can cause your instrument unstable, lower performance and more complicated problem. Cal-Tech is the only vendor know how to recalibrate and all the assemblies to the factory spec.       HP Part Number Description 5890 GC II & II Plus   05890-60015 Main board 5890 II 05890-60017 Main board 5890 II Plus     6890 GC   G1520-60010 G1520-60011 Main Board 6890A+     5970 HP MSD   05990-69008 EMV High Voltage 05970-69114 RFPA 5970 05970-69009 Main Board 05990-69012 Log Amp 05990-69408 Quad Driver Board 05990-69426 Detector Board     5971/5972 HP MSD   05971-69001 5971/5972 RFPA Top Board 05971-69002 5971 Main Board 05971-69012 5971 Main Board 05971-69018 5971 Main Board 05972-69020 5972 Main Board 05971-69003 5971 AC Board 05972-69003 5971/72 AC Board 05971-69121 GCD RFPA     5973 HP MSD   G1099-60002 Log AMP G1099-60010 Main Board G1099-60015 RFPA Side Board G1099-60003 AC Board 05990-60406 05990-60410 05990-60412 05990-60420 SmartCart II SmartCard II+ SmartCard III AS 7673 A-B-C   18594-60010 Main Control Board 7673 A 18594-60125 18594-60135 Main Control Board 7673 B 07673-60020 07673-60025 07673-60026 Injector Control Board A Injector Control Board B 18594-60075 Tray Control Board 18594-60110 HpIB Controller