Test equipment and power supplies

Agilent 669xA: troubleshooting and error codes

The ServiceForge knowledge base holds 17 documented symptoms for the Agilent 669xA, with 46 ranked causes, 60 diagnostic checks with test points and expected values, and 23 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

DAC defective

Digital-to-analog converter does not produce correct output steps or waveforms

Ranked causes

1. Bias and reference voltages out of specification (common)
2. One DAC output missing steps (occasional)
3. All DAC outputs missing steps (occasional)
4. CV or CC DAC defective (occasional)
5. Reference voltage out of specification (rare)

First check

Verify bias and reference voltages

Test point: Test points 9 through 22 per table 6-3
Expected: Within specification
Tools: DMM

3 more checks with pass and fail actions are in ServiceForge. Connect ServiceForge to your AI

Output held low

Output voltage cannot be raised above low level and PROT indicator is not illuminated

Ranked causes

1. Bias and reference voltages out of specification (common)
2. CC constant current annunciator is on (load impedance too low) (common)
3. UNR (underrange) annunciator is on (occasional)
4. A10 board defective (occasional)
5. A6 board defective (rare)

First check

Verify bias and reference voltages

Test point: Test points 9 through 22
Expected: Within specification per table 6-3
Tools: DMM

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

Calibration: Restore factory calibration constants

Recover original factory calibration constants to operate power supply for troubleshooting or recalibration. Factory preset jumper position enables restoration.

Ranked causes

1. Factory calibration constants need restoration (unknown)
2. EEPROM requires initialization after replacement (unknown)
3. Transfer new calibration constants to EEPROM Factory Cal locations (unknown)
4. Pre-initialized A1 boards available (unknown)

First check

Verify J3 jumper position on A1 Front Panel Board

Test point: J3 on A1 Front Panel Board
Expected: Jumper at FACTORY PRESET CAL position

4 more checks with pass and fail actions, 9 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

No display

Unit powers on but display is blank or non-functional

Ranked causes

1. A1 front panel board defective (common)
2. LCD DSP1 or cable W2 defective (common)
3. A2 GPIB board defective (occasional)
4. A6 board defective (occasional)

First check

Check display bias voltage

Test point: R1-6
Expected: +5V
Tools: DMM

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

Output held high high voltage

Output voltage is stuck at high level and cannot be reduced

Ranked causes

1. Bias and reference voltages out of specification (common)
2. CV OR gate diode A10D652 conducting (short circuit) (common)
3. Fast sense amplifier A10U608-7 defective (occasional)
4. A10 board defective (occasional)

First check

Verify bias and reference voltages

Test point: Test points 9 through 22
Expected: Within specification per table 6-3
Tools: DMM

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

Serial Down error

Display shows SERIAL DOWN error message indicating communication failure between front panel and control board

Ranked causes

1. GPIB board (A2) defective or not responding (common)
2. Cable W4 open or defective (occasional)
3. Secondary bias circuit defective (occasional)
4. Control board (A10) defective (occasional)

First check

Check for serial data pulses at secondary interface

Test point: A2U110-8
Expected: SERIAL DATA PULSES present with respect to PRIMARY GROUND (test point 1)

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

FET board (A3) defective high voltage

Power FET or bias circuit failure preventing proper output stage operation

Ranked causes

1. Power FET devices (Q201-204, Q301-304, Q211, Q311, Q222, Q322, Q233, Q333, Q244, Q344) shorted or defective (common)
2. Output capacitors (C201, C301) leaky or defective (occasional)
3. Bias supply or FET gate bias circuit defective (occasional)

First check

Isolate A3 FET board from supply for testing

Test point: A3 board installation
Expected: Board removed from supply with heatsink attached

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

OV at turn-on high voltage

Overvoltage circuit activates immediately when supply powers on instead of when threshold is exceeded

Ranked causes

1. Output voltage setting higher than OV setting in memory register (common)
2. Output momentarily exceeds voltage setting at turn-on (occasional)
3. A10 board or OV circuit defective (occasional)

First check

Monitor output voltage at turn-on with scope

Test point: Output terminals
Expected: Output does not exceed programmed voltage
Tools: Oscilloscope, DC coupled

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

OV will not fire

Overvoltage circuit does not respond when overvoltage condition is programmed or detected

Ranked causes

1. A6 board defective (common)
2. A10 board defective (common)
3. A10 or A9 downprogrammer board defective (occasional)

First check

Check bias and reference voltages

Test point: Test points 15 through 22
Expected: Within specification
Tools: DMM

3 more checks with pass and fail actions are in ServiceForge. Connect ServiceForge to your AI

Supply does not operate properly high voltage

Unit fails power-on selftest or operates abnormally after power-on

Ranked causes

1. GPIB board (A2) defective (common)
2. Front panel board (A1) defective (common)
3. Cable W5 defective (occasional)

First check

Verify supply basic operation

Test point: Front panel
Expected: Unit powers on without error messages

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

Slow Down Programming error

Display shows SLOW DOWN PROGRAMMING error indicating slow response during programming of output voltage and current

Ranked causes

1. Control board (A10) defective or degraded performance (common)
2. Power supply board (A9) fuses open or defective (occasional)

First check

Program output voltage and current to half scale

Test point: Front panel controls
Expected: Output voltage and current set to 1/2 full scale

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

CAL DENIED displayed or error code 1 (GPIB)

Front panel calibration attempt shows CAL DENIED message or GPIB calibration returns error code 1 on Systems Supply, preventing access to calibration mode.

Ranked causes

1. INHIBIT CAL jumper installed (common)

First check

Verify INHIBIT CAL jumper location

Test point: INHIBIT CAL jumper (Figure 3-15)
Expected: NORM position (not INHIBIT CAL position)

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

Calibration: Current programming and readback accuracy high voltage

Verify programmed current matches actual output for each model

Ranked causes

1. Out-of-spec current output (unknown)

First check

Measure output current

Test point: Output terminals
Expected: See Table 2-2 for model: 6690A 440A, 6691A 220A, 6692A 110A

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

Calibration: Post-repair adjustment

Annual calibration or after component replacement in CV/CC DACs, operational amplifiers, control circuits, readback DAC/comparators, front panel board, or EEPROM. Required to verify output accuracy after service.

Ranked causes

1. Component replacement in control or readback circuits (common)

First check

Verify INHIBIT CAL jumper position

Test point: INHIBIT CAL jumper (Figure 3-15)
Expected: NORM position

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

Calibration: Transfer factory preset calibration data

Transfer calibration constants from operating locations to EEPROM factory preset locations after calibration and alignment complete. Requires program execution.

Ranked causes

1. New calibration constants need storage in factory preset locations (unknown)

First check

Input power supply model number to program

Test point: Program input prompt
Expected: 6690A, 6691A, or 6692A

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

EEPROM initialization after component replacement

Reinitialize EEPROM AlU6 on A1 Front Panel Board after board or EEPROM replacement to load proper GPIB address, model number, and programming/calibration constants.

Ranked causes

1. Front Panel Board or EEPROM replaced (unknown)

First check

Verify component replacement

Test point: A1 Front Panel Board and EEPROM AlU6
Expected: Board or EEPROM component replaced

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

PASSWD ERROR displayed or error code 2 (GPIB)

Calibration mode entry failed with PASSWD ERROR message on front panel or error code 2 via GPIB, indicating incorrect or unknown calibration password.

Ranked causes

1. Incorrect calibration password entered (common)

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

Error codes

Code	Meaning	Trigger	Severity
`1`	Calibration inhibited or unable to enter calibration mode via GPIB on Systems Supply	INHIBIT CAL jumper in INHIBIT CAL position when GPIB calibration is attempted	error
`2`	Incorrect or unknown calibration password entered	User enters wrong password when attempting to enter calibration mode via front panel or GPIB	error
`E10 SEC 5V`	Secondary interface 5 volt readback test failed	Power-on and *TST?	error
`E11 TEMP`	Ambient temperature readback test failed	Power-on and *TST?	error
`E12 DACS`	CV or CC DAC tests failed	Power-on selftest	error
`E1 FP RAM`	Front panel RAM test failed	Power-on selftest	error
`E2 FP ROM`	Front panel ROM test failed	Power-on and *TST?	error
`E3 EE CHKSM`	Front panel EEPROM checksum test failed	Power-on and *TST?	error
`E4 PRI XRAM`	Primary interface external RAM test failed	Power-on selftest	error
`E5 PRI IRAM`	Primary interface internal RAM test failed	Power-on selftest	error
`E6 PRI ROM`	Primary interface ROM test failed	Power-on and *TST?	error
`E7 GPIB`	GPIB interface test failed	Power-on selftest	error
`E8 SEC RAM`	Secondary interface RAM test failed	Power-on selftest	error
`E9 SEC ROM`	Secondary interface ROM test failed	Power-on and *TST?	error
`EE WRITE ERR`	EEPROM write failure	During operation or selftest	error
`SBUF FULL`	Serial buffer full condition	During operation or selftest	error
`SBUF OVERRUN`	Serial buffer failure	During operation or selftest	error
`SECONDARY DN`	Serial data line failure on Main board	During operation or selftest	error
`SERIAL DOWN`	Serial data line failure on A2 board	During operation or selftest	error
`SERIAL TIMOUT`	Serial data line failure on A2 board	During operation or selftest	error
`UART FRAMING`	UART failed framing check	During operation or selftest	error
`UART OVERRUN`	UART buffer overrun	During operation or selftest	error
`UART PARITY`	UART failed parity check	During operation or selftest	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.