Test equipment DC power supplies

Agilent 6625A: troubleshooting and error codes

The ServiceForge knowledge base holds 26 documented symptoms for the Agilent 6625A, with 53 ranked causes, 57 diagnostic checks with test points and expected values, and 11 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Output board component failure high voltage

Output board malfunction detected; need to isolate fault to specific component or circuit

Ranked causes

1. DAC/amplifier circuit failure (unknown)
2. Analog Multiplexer U323 failure (unknown)
3. Signal Processor U327 failure (unknown)
4. Power Module U338/U339 failure (unknown)
5. Microcomputer U312 failure (unknown)

First check

Disconnect the line cord

Test point: AC power input
Expected: System powered off safely

4 more checks with pass and fail actions, 5 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Unit does not pass power-on self test

Display shows blank or ERR message during power-on self test sequence

Ranked causes

1. AC input failure (common)
2. Defective GPIB board (occasional)
3. Defective display (occasional)
4. Defective output board (occasional)
5. Cabling problem (occasional)

First check

Power on unit and observe display

Test point: Front panel display
Expected: Display shows normal power-on self test indications as described in Operating Manual Section III

5 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

GPIB board or front panel malfunction high voltage

GPIB board circuit bias voltages incorrect; front panel display inoperative; microprocessor clock, RAM, or ROM circuit failure; front panel LEDs or controls not responding.

Ranked causes

1. GPIB board bias voltage failure (common)
2. Microprocessor clock failure (occasional)
3. RAM or ROM circuit failure (occasional)
4. Defective component identified by signature analysis (occasional)

First check

Verify GPIB board bias voltages

Test point: GPIB board circuits and front panel display
Expected: Correct bias voltages present

4 more checks with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Incorrect or multiple output status reported caution

Output reports wrong status (CV, CC, OV, OT, UNR) or multiple simultaneous statuses when queried

Ranked causes

1. Status monitor circuit U327 failure (rare)
2. Microcomputer U312 failure (rare)
3. Short on data lines between U327 and U312 (occasional)
4. Load transient causing temporary multiple status (common)

First check

Query output status and observe front panel status indicators

Test point: Output status lines
Expected: Single valid status condition (CV, +CC, -CC, OV, OT, or UNR)

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Incorrect or multiple status reported

Output operates properly but status display (CV, CC, OV, OT, UNR) is wrong or multiple statuses shown simultaneously

Ranked causes

1. Status monitor circuit of U327 faulty (common)
2. Microcomputer U312 faulty (common)
3. Short on data lines between U327 and U312 (occasional)
4. Load transient causing temporary multiple status (occasional)

First check

Observe STATUS SELECT line on oscilloscope

Test point: U327 pin 11
Expected: goes low for about 30 µS
Tools: oscilloscope

2 more checks with pass and fail actions, 3 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Instrument damaged by electrostatic discharge during maintenance caution

Static-sensitive semiconductors and components degraded or failed due to electrostatic charge exposure during handling or maintenance

Ranked causes

1. Handling static-sensitive components without proper ESD protection (common)
2. Components installed or removed with power applied (common)
3. Conductive equipment or devices not grounded in work area (occasional)
4. Use of static neutralizer instead of direct grounding (rare)

First check

Verify work station conductive surface resistance

Test point: Work surface
Expected: Distributed resistance between 10^6 and 10^12 ohms per square

2 more checks with pass and fail actions, 6 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Component failure after replacement or repair caution

Component or circuit on board failed after service technician completed maintenance; system test performance degradation or failure

Ranked causes

1. GPIB board or EEPROM not recalibrated after replacement (common)
2. Output board replaced without output channel recalibration (common)
3. Output or readback circuit component replaced without calibration (common)

First check

Verify GPIB board and EEPROM calibration status

Test point: GPIB board, EEPROM U221
Expected: Recalibration completed after replacement

2 more checks with pass and fail actions, 3 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Analog multiplexer U323 readback voltage incorrect

VMUX? command returns unexpected voltage reading from selected multiplexer input

Ranked causes

1. Analog multiplexer U323 or readback switches U365/U366 malfunction (unknown)
2. Readback signal comparator U324 failure (unknown)

First check

Run VMUX? command on each of 18 analog multiplexer inputs

Test point: U323 inputs 1-18
Expected: Response format SZD.DDDD with resolution approximately 0.5 mV
Tools: GPIB interface, external voltmeter

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Calibration: MODEL command firmware reset

After issuing MODEL command to reset firmware to default values, all calibration constants are removed and each output must be recalibrated

Ranked causes

1. Firmware reset via MODEL command clears calibration data (common)
2. Power cycle required to complete firmware initialization (common)

First check

Set CMODE to command mode

Test point: OUTPUT 705
Expected: CMODE 1

5 more checks with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

GPIB board replacement high voltage

GPIB board replaced or EEPROM chip (U230 or U231) replaced. Recalibration and model number setting required.

Ranked causes

1. EEPROM lost model number and GPIB address settings after replacement (common)
2. Output calibration values lost (common)

First check

Verify EEPROM model number setting

Test point: EEPROM U230 or U231
Expected: Model number and letter suffix match unit (e.g. 6626A)

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Output board component replacement and recalibration high voltage

Procedures for replacing output board components and subsequent calibration requirements

Ranked causes

1. Output board replacement (unknown)
2. Output circuit component replacement (unknown)

First check

Replace defective output board or component

Test point: Output board
Expected: New board or component installed and properly seated

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Signal Processor U327 pin voltage out of range

Pin voltages do not match expected levels defined in Table 4-17 during functional verification

Ranked causes

1. Analog multiplexer U323 or readback circuitry defective (common)
2. Circuitry associated with single input defective (occasional)

First check

Measure +5 V bias voltage on pin 1

Test point: U327 pin 1
Expected: 4.72 V to 5.23 V, 4.72–5.23 V
Tools: DMM

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

-15 V bias voltage out of range caution

Measured -15 V bias supply voltage is outside specified range

Ranked causes

1. Unregulated bias supply voltage too low or too high (common)

First check

Measure -15 V bias supply voltage

Test point: pin 28
Expected: -15.55 V to -13.98 V, -15.55 to -13.98
Tools: DMM

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration locked

Error 18 (CAL LOCKED) generated when attempting to enable calibration mode

Ranked causes

1. Jumper W201 in CAL. LOCKOUT position (common)

First check

Verify jumper W201 position on connector P201

Test point: Connector P201
Expected: +5V NORM RUN position

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration required

Supply passes all functional tests but requires calibration adjustment

Ranked causes

1. Output voltage or current out of specification (unknown)

First check

Verify output voltage and current accuracy against specification

Test point: Output terminals
Expected: Voltage and current measurements within specification limits

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Error 22 SKIP SELF TEST generated at power-on

Error 22 message appears when power supply is first turned on with W201 in SKIP SELF TEST position

Ranked causes

1. W201 jumper in SKIP SELF TEST position during power-on (common)

First check

Observe if error 22 clears after being read

Test point: Front panel display
Expected: Error 22 disappears after reading

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Firmware revision identification and querying

ROM chip U206 on GPIB board identifies firmware revision by label or ROM? command query; revision A.00 has date code 2839 (1988, week 39)

Ranked causes

1. Need to identify firmware revision for troubleshooting (unknown)

First check

Locate ROM chip U206 label on GPIB board

Test point: ROM chip U206
Expected: Label present with firmware revision code

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MODEL command recalibration required

After executing MODEL command to reset firmware, recalibration must be performed for all outputs

Ranked causes

1. MODEL command executed, resetting calibration to defaults (common)

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Output board RAM or ROM failure detected

Errors 11, 12, 13, or 14 (HDW ERR CH) generated when output board RAM or ROM tests fail

Ranked causes

1. Output board RAM or ROM test failure (rare)

First check

Determine which output channel has failed

Test point: Error code display
Expected: Error 11, 12, 13, or 14 indicating channel number

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Output channel cannot be programmed from front panel

Output channel does not respond to front panel programming commands after passing self test

Ranked causes

1. Output board defect (unknown)

First check

Attempt to program each output channel from front panel controls

Test point: Front panel programming interface
Expected: Output voltage and current settings respond to front panel adjustments

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Output channel cannot be programmed from GPIB controller

Output channel does not respond to programming commands sent over GPIB interface

Ranked causes

1. GPIB board defect (unknown)

First check

Send programming commands to output channels via GPIB controller

Test point: GPIB interface connector
Expected: Output voltage and current settings change in response to GPIB commands

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Output voltage less than programmed voltage

Voltage regulation circuit detects output below setpoint; control loop attempts to increase voltage through base drive circuit conduction

Ranked causes

1. Voltage below programmed setpoint in voltage control mode (unknown)

First check

Compare output voltage to programmed voltage setting

Test point: Output terminals
Expected: Output voltage equal to or greater than programmed voltage

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Safety hazards during maintenance with covers removed high voltage

Technician exposure to electrical shock or fire hazard while performing maintenance with power applied and covers removed

Ranked causes

1. Maintenance performed by untrained personnel with power applied (rare)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Self exercise routine activation for output board diagnostics high voltage

Enter self exercise mode to test microcomputer U312 and all DACs for troubleshooting

Ranked causes

1. Need to activate self-test for diagnostics (unknown)

First check

Create short between U312 pin 6 and pin 7 before power-on

Test point: U312 pin 6 and pin 7
Expected: Short connected

4 more checks with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Self-test bypassed patient safety

Power supply skips power-on self tests when W201 in SKIP SELF TEST position; output may operate beyond rated parameters

Ranked causes

1. Jumper W201 in SKIP SELF TEST position (common)

First check

Verify jumper W201 position

Test point: Connector P201
Expected: +5V NORM RUN position

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Signature Analysis testing setup

Signature analysis is a troubleshooting method for microprocessor-based circuits; bit streams are compressed into 4-character signatures to isolate faults to 1-2 components

Ranked causes

1. GPIB board or peripheral circuit failure requiring diagnosis (unknown)

First check

Check for Vcc (+5V) and ground signatures on IC

Test point: IC pins
Expected: Known Vcc and ground reference signatures

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Error codes

Code	Meaning	Trigger	Severity
`11`	HDW ERR CH (Hardware Error Channel)	Output board fails RAM or ROM tests during power-on or operation	critical
`11`	HDW ERR CH 1	Output board channel 1 fails RAM or ROM self-test	error
`12`	HDW ERR CH (Hardware Error Channel)	Output board fails RAM or ROM tests during power-on or operation	critical
`12`	HDW ERR CH 2	Output board channel 2 fails RAM or ROM self-test	error
`13`	HDW ERR CH 3	Output board channel 3 fails RAM or ROM self-test	error
`13`	HDW ERR CH (Hardware Error Channel)	Output board fails RAM or ROM tests during power-on or operation	critical
`14`	HDW ERR CH (Hardware Error Channel)	Output board fails RAM or ROM tests during power-on or operation	critical
`14`	HDW ERR CH 4	Output board channel 4 fails RAM or ROM self-test	error
`18`	CAL LOCKED	Attempt to enter calibration mode when W201 jumper in CAL. LOCKOUT position	info
`22`	SKIP SELF TEST	W201 jumper in SKIP SELF TEST position at power-on	warning
`ERR`	Power-on self test error or failure	One or more tests in power-on self test sequence detect a failure on GPIB board or output board	error

Likely causes and actions for each code are in ServiceForge. Connect ServiceForge to your AI

Community

0 fixes logged by technicians through their AI, with outcomes, for this model.

ServiceForge knowledge base record. Field-unverified unless technicians confirmed it. A teaching summary of the record, not a service manual. Export 2026-10-14.