Agilent Technologies 7820A

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Agilent 7820 GC Service

279

Multiplexed ADC

This information is based on Service Mode | Diagnostics |

Electronics | Multiplexed ADC.

MULTIPLEXED ADC

Definition

Oven rtd

Reading noise

159.8

Reading value

1801821

Offset

54907

Gain

counts/volt

4173672

Gain counts/ohm

14607

Reference

Temperature

95.446

Reading value

1801887

Reading value

-95

Reading value

-180

Reading value

198

Reading value

-45

There is a multiplexed analog-to-digital circuit (ADC) for each of

the following resistance temperature detectors (rtd):

Main Page

Notices2
- Table of Contents3
1 Before Servicing the Instrument13
Safety14
Hand Tools14
Specialized Tools15
Electronic Tools17
Pneumatic Tools18
For Checking Inlet Pressure19
2 Inlets23
Inlet Overview24
Split/Splitless Inlet24
- Replacing the Split/Splitless Inlet24
- Replacing the Split/Splitless Inlet Top Weldment Assembly26
- Replacing the Split/Splitless Inlet Split Vent Line27
- Replacing the Split/Splitless Inlet Split Vent Filter Canister and Valve Assembly28
- Reinstalling the Split/Splitless Inlet29
Purged Packed Inlet31
- Replacing the Purged Packed Inlet31
- Replacing the Purged Packed Inlet Heater35
3 Detectors39
About the Detector Signal Boards40
Detector Overview40
Accessing Detector Signal Boards41
Replacing Detector Signal Boards41
Flame Ionization Detector (FID)44
- Selecting an FID Jet44
- Replacing the FID Interconnect Assembly or Spring46
- Replacing the Heater48
- Replacing the FID Signal Board53
- Replacing the Electrometer54
- Replacing the Glow Plug (Ignitor)55
- Replacing the Entire FID57
- Ultrasonic Cleaning the FID62
Nitrogen Phosphorus Detector (NPD)65
- Selecting an NPD Jet65
- Removing the NPD Electrometer66
- Replacing the Entire NPD67
- Replacing an NPD Signal Board70
- Replacing the NPD Heater72
- Replacing the NPD Electrometer74
- Cleaning the NPD Jet and Collector76
- Cleaning the NPD78
Thermal Conductivity Detector (TCD)81
- Replacing the TCD Detector Cell81
- Replacing the TCD Switching Valve83
Micro-Cell Electron Capture Detector (Uecd)85
- Replacing the Uecd Heater/Sensor Assembly85
- Replacing the Uecd Makeup Gas Adapter86
- Frequency Test87
- Leak Test89
- Performing a Radioactivity Leak Test (Wipe Test)89
Flame Photometric Detector (FPD)91
- Preparing for Maintenance91
- Disassembling the FPD91
- Rebuilding the FPD Optics Assembly101
- Reassembling the FPD108
- Replacing the FPD117
- Bake out and Run Checkout Test119
- Replacing the Heater/Sensor Assemblies119
- Replacing the FPD Signal Board123
4 EPC Modules125
EPC Overview126
Repairing EPC Modules126
Accessing EPC Modules127
Replacing the EPC Modules128
Replacing EPC Module Proportional Valves129
5 Performance Verification131
About Chromatographic Checkout131
To Prepare for Chromatographic Checkout132
To Check FID Performance132
- Typical Values136
To Check NPD Performance136
- Typical Values140
To Check TCD Performance140
To Check Uecd Performance145
- Typical Values149
To Check FPD Performance (Sample 5188-5953)150
6 Configuration157
Configuration Overview158
- Inlet Example159
- Detector Example159
- PCM Example160
- Heater Assignments161
GC Modules and the Communications Buss163
To Configure an MSD Transfer Line165
To Configure a Valve Box166
Replacing a GC Module166
Removing a GC Module167
Changing the GC Configuration167
Configuration Locks168
Installing New Devices169
Configuring Time170
7 External Cabling171
Connectors on the Back of the GC172
Remote Start/Stop172
- APG Remote Control172
- Cable Pinouts, Remote Start/Stop, General Use176
- Cable Pinouts, GC to 3395B/3396C Integrator177
Automatic Sampler for GC177
Analog Signal Outputs178
- Analog Cable: GC to 3395A/B or 3396B/C Integrators and 35900 C/D/E Analog to Digital Interface Instrument178
- Analog Cable: General Use179
8 Internal Cabling181
Internal Cabling Overview182
Ignitor Cable, FID182
NPD Power Cable183
Motor Harness & AC Control Assembly184
AC Power Inlet Assemblies184
Inlet/Detector Heater Harness187
Aux Heater/Valve Box Harness188
Communications Harness188
7820 GC/MS Second Inlet Upgrade Harness191
Keyboard Display Cable192
Display Cable Assembly192
9 Mainframe193
Mainframe Overview194
Covers and Fans194
- Removing and Replacing the Covers194
- Replacing the Oven Bezel196
- Replacing the Inlet Cooling Fan196
- Replacing the EPC Cooling Fan197
Replacing the Oven Door199
Oven Temperature Control200
Oven Temperature Troubleshooting200
Measuring Inlet and Detector Heater and PRT Resistance201
Testing Resistance of the Oven Heater Coil203204
Replacing the Oven Shroud, Oven Fan, and Oven Fan Motor205
- Replacing the Oven Shroud, Oven Fan, and Oven Fan205
- Motor205
Replacing the Oven Flapper Assembly208
Replacing Components Inside the Electronics Panel209
- Accessing the Analog and Power Board209
- Replacing the als Board209
- Replacing the Fuse on the als Controller Board212
- Removing the Valve Bracket214
- Replacing the Logic Board216
- Replacing the Analog and Power Board220
Replacing Components Inside the Lower Rear Metal Cover223
- Replacing the AC Board223
- Replacing the Oven Triac224
- Replacing the Power Transformer226
10 Valves229
Valves230
- Introduction230
- Valco W-Series Minivalves231
- Gas Sample Valves233
Valve Box234
- Installing the Valve Box234
- Removing the Valve Box Assembly238
Actuators240
- Installing the Actuators240
- Valve Actuator Drivers242
  - Replacing a Solenoid Valve (New Style)242
- Valve Actuator Alignment246
Typical Valve Configurations247
- Custom Plumbing (Diagram Required), Option247
- Gas Sampling Option, Option 701 or 751248
- Column Isolation, Option 702 or 752248
- Two Stream Selection (Requires Gas Sampling), Option 703 or 753249
- Custom Plumbing (Diagram Required), Option249
- Gas Sampling with Backflush of Precolumn to Vent, Option 801250
- Gas Sampling with Backflush to Detector, Option250
- Gas Sampling with Sequence Reverse and Backflush of Column 1, Option 805251
Troubleshooting252
- Chromatographic Symptoms252
- Loss of Sensitivity or Excessive Drift253
- Loss of Peaks in Specific Areas of the Chromatogram253
- Extraneous Peaks253
- Peak Broadening and Tailing254
- Baseline Shifts254
- Baseline Upsets254
- Variation in Peak Area and Retention Time255
- Pressure Check255
11 Electrical257
Power Options258
Converting the Power Option259
Remote Start/Stop Connection261
Remote Control262
Temperature Sensor Resistance263
Ceramic and Glass Fuses263
AC Power Board Schematic264
Oven Shroud265
12 Firmware267
Firmware Overview268
Confirm Firmware Update268
To Update GC Firmware269
To Update Frit Constants271
13 Service Mode Diagnostics275
Service Mode Overview276
Detector Diagnostics276
Signal Board Diagnostics277
Multiplexed ADC279
Pneumatics280
Power Diagnostics281
14 Printed Circuit Boards283
AC Power Board285
Analog and Power Board287
Logic and Communications Board288
Keyboard Interconnect Board288
FID Signal Board290
TCD Signal Board291
Uecd Signal Board292
NPD Signal Board292
FID Electrometer Board293
Uecd Electrometer Board294
NPD Electrometer Board294
FPD Signal Board296
15 Illustrated Parts Breakdown297
Overview of the IPB297
Inlets298
- Split/Splitless Inlet (SSL)299
- Purged Packed Inlet (PP)307
Detectors316
- Flame Ionization Detector (FID)317
- Thermal Conductivity Detector (TCD)325
  - Thermal Conductivity Detector (TCD)327
  - Consumables for the TCD330
- Microcell Electron Capture Detector (Uecd)331
  - Microcell Electron Capture Detector (Uecd)333
  - Consumables for the Uecd338
- Nitrogen Phosphorus Detector (NPD)340
  - Nitrogen Phosphorus Detector (NPD)342
  - Consumables for the NPD345
- Flame Photometric Detector (FPD)348
EPC Modules358
Nickel Catalyst Accessory366
Covers369
- Mainframe371
Automatic Liquid Sampler Parts372
Oven374
- Oven Assembly374
- Oven Flapper Assembly376
Valves378
- Valve Box Assembly378
- Valve Driver Assembly380
- Valve Actuator Assembly (1 of 2)382
- Valve Actuator Assembly (2 of 2)383
- Valco W-Series Minivalve384
Electrical387
- Electronics Carrier387
- Display and Keyboard389
- AC Power Components390
- AC Circuit Board Components393
- AC Power Kits394
- Main Transformer395
- Power Cords396
- Chassis Fans397

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