Test equipment and power supplies

Agilent 66312A: troubleshooting and error codes

The ServiceForge knowledge base holds 34 documented symptoms for the Agilent 66312A, with 65 ranked causes, 101 diagnostic checks with test points and expected values, and 22 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 current less than rating high voltage

Power supply output current below specified maximum rating; control voltage and feedback circuits may be at fault

Ranked causes

1. Interface board current control failure (unknown)
2. Current monitoring voltage incorrect (unknown)
3. U324A/B current feedback amplifier failure (unknown)
4. Control or downprogrammer circuit fault (unknown)
5. U321A or R360 circuit fault (unknown)
6. U321B or voltage sense circuit failure (unknown)
7. Output transistor stage not conducting (unknown)

First check

Measure CC_Prog voltage at R336

Test point: R336 (CC_Prog)
Expected: <= -4.8V

5 more checks with pass and fail actions, 7 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Power-on self-test failure

Display shows ERR annunciator; output is not disabled; query unit to determine specific error codes

Ranked causes

1. ROM checksum error (common)
2. RAM test failure (common)
3. DAC test failure (common)
4. RS-232 communication error (occasional)
5. Front Panel communication error (occasional)

First check

Query unit to determine specific error code

Test point: Unit interface
Expected: Error code E1–E5 (ROM checksums), E10–E15 (DAC tests), E80 (I/O test), E213–E223 (communication errors)

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

Protection activated high voltage

Unit is in protection mode (FS, OT, OC, OV, RI); output disabled

Ranked causes

1. Overvoltage protection triggered (common)
2. Overcurrent protection triggered (common)
3. Over-temperature protection (occasional)
4. Remote inhibit active (occasional)

First check

Observe protection annunciator state

Test point: front panel protection indicator
Expected: annunciator off

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

Bias and reference voltage out of range

Check bias and reference voltages before troubleshooting circuits; voltages out of spec indicate power supply issue

Ranked causes

1. Primary +5V out of specification (common)
2. Secondary voltage supply failure (common)
3. Reference voltage out of tolerance (occasional)

First check

Measure primary +5V supply

Test point: A1 J206-1
Expected: +5V, +/- 0.15V
Tools: DMM

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

Calibration: Post-repair procedures

Annual calibration or recalibration required after component replacement in voltage/current monitor or interface circuits

Ranked causes

1. Component replacement in A1 Control Board voltage/current monitor circuits (common)
2. Component replacement in A1 Control Board current monitor resistors R425/R431 (common)
3. A2 Interface Board replacement (common)

First check

Verify INHIBIT CAL switch S201 configuration

Test point: S201 on A2 Interface board, switches 3 and 4
Expected: Switch 3 Off, Switch 4 Off for Normal operation

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

CV/CC annunciator troubleshooting with no output

CV or CC annunciator on indicates problem in associated control circuit; UNR indicates neither circuit in control

Ranked causes

1. Voltage Amplifier circuit failure (common)
2. Current Amplifier circuit failure (common)
3. Output stage failure (occasional)

First check

Measure voltage drop across CV gating diode

Test point: A1 D317
Expected: Forward drop present if CV mode active; low signal at U328C output (CV_DETECT*)

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

No display on unit high voltage

Front panel display is not powered on when unit is turned on

Ranked causes

1. AC input failure (common)
2. Line voltage selection incorrect (occasional)
3. Bias supply failure (occasional)

First check

Verify display is powered after power-on

Test point: front panel display
Expected: display illuminated

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

Slow down programmer output voltage incorrect high voltage

When external supply applies 5V at 2A across output, meter indicates incorrect voltage or current

Ranked causes

1. U321A output amplifier error (unknown)
2. U308A output stage failure (unknown)
3. Q306 or Q309 control stage issue (unknown)

First check

Measure voltage at meter output with 5V 2A applied

Test point: Meter output
Expected: 5V -1.5A

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

Calibration password incorrect or forgotten

Incorrect password entered during calibration attempt; OUT OF RANGE or error 402 displayed

Ranked causes

1. Incorrect calibration password entered (common)
2. Calibration password forgotten (occasional)

First check

Verify password entry

Test point: Front panel display or GPIB calibration mode
Expected: Correct password accepted; calibration mode enabled

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

Current output out of specification high voltage

Programmed current limit does not match actual measured output current

Ranked causes

1. Current calibration needed (common)
2. Interface board failure (occasional)

First check

Check CC_PROG voltage at R336

Test point: R336
Expected: 0 to -4.8 V for 0 to full scale programmed current, 0 to -4.8 V

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

Fan not operating caution

Cooling fan does not run even when unit is powered on

Ranked causes

1. Low or missing 15V bias supply (common)
2. Fan driver circuit failure (occasional)

First check

Observe fan operation during power-on

Test point: cooling fan
Expected: fan rotates smoothly

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

J307 voltage measurement out of range

J307 connects A1 Main Board to A2 Interface Assembly; out-of-range voltages indicate circuit problem on A1 or A2

Ranked causes

1. CV Mode voltage outside specification (common)
2. CC Mode voltage outside specification (common)

First check

Measure PM_INHIBIT at J307 pin 1

Test point: A1 J307 pin 1
Expected: 0V when enabled
Tools: DMM

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

No output voltage high voltage

Output terminals show zero voltage or less than minimum programmed value

Ranked causes

1. Gated bias supply failure (common)
2. Series regulator failure (occasional)

First check

Measure gated +/-15V at fuse holders F302 and F304

Test point: F302, F304
Expected: ±15 V DC, ±15 V

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

Output held high high voltage

Output remains at high voltage level and will not decrease when attempting to reduce programmed voltage

Ranked causes

1. Series pass element stuck (occasional)
2. Feedback circuit failure (occasional)

First check

Disable OV protection via DIAG:SCR 0 command

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

Output voltage out of specification high voltage

Programmed voltage does not match actual measured output voltage

Ranked causes

1. Voltage calibration needed (common)
2. Interface board failure (occasional)

First check

Program full scale voltage and current; enable output

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

Overvoltage at turn-on high voltage

Output voltage spikes high when unit is powered on; OV protection activates

Ranked causes

1. OV detection circuit failure (occasional)
2. Incorrect OV protection setting (common)

First check

Connect scope DC coupled across output during power-on

Test point: output terminals
Expected: output stays below OV limit

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

20 mA range current readback accuracy out of specification at 0 A

Current readback in 20 mA range differs from DMM measurement at zero amps beyond specified limits

Ranked causes

1. Low current range readback circuit calibration error (unknown)

First check

Measure 20 mA range current readback at 0 A

Test point: DMM in current mode
Expected: difference within specified limits per performance test record chart 20mA RANGE CURRENT READBACK ACCURACY @ 0A
Tools: DMM

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

20 mA range current readback accuracy out of specification at 20 mA

Current readback in 20 mA range differs from DMM measurement at 20 mA beyond specified limits

Ranked causes

1. Low current range readback circuit error at 20 mA (unknown)

First check

Measure 20 mA range current readback at 20 mA

Test point: DMM in current mode
Expected: difference within specified limits per performance test record chart 20mA RANGE CURRENT READBACK ACCURACY @ 20mA
Tools: DMM

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

Calibration switch CAL DENIED or error 401

Calibration mode denied due to INHIBIT CAL switch setting

Ranked causes

1. INHIBIT CAL switch S201 set to inhibit calibration (common)

First check

Check S201 switch 3 and 4 configuration

Test point: S201 on A2 Interface board
Expected: Switch 3 Off, Switch 4 Off for Normal; Switch 3 On, Switch 4 Off for Inhibit Calibration

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

Calibration: Power supply initialization

Re-initialize EEPROM on A2 Interface board after replacement; required before calibration

Ranked causes

1. Interface board replaced (unknown)

First check

Enable Calibration mode

Test point: Front panel
Expected: Calibration mode active

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

Calibration: ROM upgrade procedure

Upgrade Interface board ROM without affecting existing calibration data in EEPROM

Ranked causes

1. ROM upgrade required (unknown)

First check

Enable Calibration mode and press '0' and '1' keys simultaneously

Test point: Front panel
Expected: EEINIT <model> displayed

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

CC load effect out of specification

Change in output current from full-scale voltage to short circuit exceeds specified limit

Ranked causes

1. Output stage or current feedback regulation inadequate (unknown)

First check

Verify CC mode operation at full-scale voltage

Test point: UUT CC annunciator
Expected: annunciator illuminated

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

CC source effect out of specification high voltage

Change in output current from minimum to maximum line voltage exceeds specified limit

Ranked causes

1. Line voltage regulation or supply regulation inadequate (unknown)

First check

Set line voltage to nominal value

Test point: Variable voltage transformer
Expected: nominal line voltage
Tools: Variable voltage transformer

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

Current programming and readback accuracy out of specification at 0 A

Current readback does not match programmed value within specified limits at zero amps

Ranked causes

1. Current monitoring circuit calibration drift (unknown)

First check

Measure current readback at 0 A programming point

Test point: Current monitoring resistor
Expected: within specified limits per performance test record card CC PROGRAMMING @ 0 AMPS
Tools: DVM

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

Current programming and readback accuracy out of specification at full-scale

Current readback does not match programmed value within specified limits at full-scale current

Ranked causes

1. Current monitoring circuit calibration drift at full-scale (unknown)

First check

Measure current readback at full-scale programming

Test point: Current monitoring resistor
Expected: within specified limits per performance test record card CC PROGRAMMING @ FULL-SCALE
Tools: DVM

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

Current sink operation or readback out of specification

Negative current (sink) operation does not function correctly or readback differs from expected value

Ranked causes

1. Current sink circuitry malfunction or readback error (unknown)

First check

Verify current sink operation produces ~-1.4 A display reading

Test point: UUT display
Expected: approximately −1.4 A

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

CV load effect exceeds specification high voltage

Output voltage change when load current changes from full load to no load exceeds maximum allowable value

Ranked causes

1. Output impedance too high or regulation circuit degraded (unknown)

First check

Record DVM voltage with full-scale current load

Test point: +S and -S terminals
Expected: Stable reading at programmed full-scale voltage

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

CV noise (PARD) exceeds specification

Peak-to-peak or RMS ripple and noise voltage on output exceeds maximum allowable limits

Ranked causes

1. Output filter capacitors degraded or switching noise coupling to output (unknown)

First check

Measure peak-to-peak noise on oscilloscope

Test point: (+) and (-) output terminals
Expected: Peak-to-peak voltage not to exceed CV NOISE (PARD) limit per performance test record chart
Tools: Oscilloscope with 20 MHz bandwidth limit, RF tip probe

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

CV source effect exceeds specification high voltage

Output voltage change when input ac line voltage varies from minimum to maximum rated value exceeds limit

Ranked causes

1. Line voltage regulation circuit degraded or ac filter insufficient (unknown)

First check

Set transformer to nominal line voltage and program supply

Test point: AC power input
Expected: Supply stable at nominal voltage

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

Disable protection features for troubleshooting caution

Protection features can be disabled except for overvoltage protection; resets to default at power-up

Ranked causes

1. Protection features interfering with troubleshooting (rare)

First check

Press 0 and 1 keys simultaneously

Test point: Front panel keys
Expected: EEINIT <model> displayed

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

Manual fan speed control caution

Reduce fan speed manually for testing where fan noise interferes; resets to Automatic at power-up

Ranked causes

1. Fan noise interfering with test (rare)

First check

Press 0 and 1 keys simultaneously

Test point: Front panel keys
Expected: EEINIT <model> displayed

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

Slow down-programming high voltage

Output voltage decreases slowly or not at all when programmed to lower value

Ranked causes

1. Down-programmer circuit fault (occasional)

First check

Program voltage up and then down

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

Transient recovery time out of specification

Output voltage does not return to specified value within specified time following 50% load current change

Ranked causes

1. Transient response characteristics degraded (unknown)

First check

Verify output voltage recovery time on loading transient

Test point: +S and -S terminals
Expected: within specified voltage in less than specified time
Tools: Oscilloscope

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

Voltage programming and readback accuracy out of spec high voltage

DVM and front panel display readings do not match specification limits when programming to zero volts or full-scale voltage

Ranked causes

1. Voltage programming circuit malfunction (unknown)

First check

Measure DVM voltage at +S to -S at zero volts programming

Test point: +S and -S terminals
Expected: Within CV PROGRAMMING @ 0 VOLTS limits per performance test record chart

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

Error codes

Code	Meaning	Trigger	Severity
`401`	Calibration inhibited by INHIBIT CAL switch setting	Attempt to calibrate over GPIB when S201 INHIBIT CAL switch is set to On	warning
`402`	Incorrect calibration password entered over GPIB	GPIB calibration command with wrong password	warning
`E1`	Checksum in Read-only Non-volatile ROM	ROM checksum validation failure during self-test	critical
`E10`	RAM test failed	RAM memory validation failure during self-test	critical
`E11`	12 bit DAC test failed at 0 input	0 written to DAC U241A and B; ADC U242 not reading 133 +/- 7 counts	critical
`E12`	12 bit DAC test failed at 4095/0 input	4095 written to DAC U241A and 0 to B; ADC U242 not reading 71 +/- 7 counts	critical
`E13`	12 bit DAC test failed at 0/4095 input	0 written to DAC U241A and 4095 to B; ADC U242 not reading 71 +/- 7 counts	critical
`E14`	12 bit DAC test failed at 4095 input	4095 written to DAC U241A and B; ADC U242 not reading 10 +/- 7 counts	critical
`E15`	8 bit DAC test failed	10 and 240 written to DAC U244; ADC U242 not reading 10 and 240 +/- 7 counts	critical
`E2`	Checksum in Config Non-volatile ROM	Configuration ROM checksum validation failure during self-test	critical
`E213`	RS-232 input buffer overrun	Serial communication data received faster than processed	error
`E216`	RS-232 framing error	RS-232 data frame format violation detected	error
`E217`	RS-232 parity error	RS-232 parity check validation failure	error
`E218`	RS-232 UART input overrun	RS-232 UART receives data while buffer still processing previous data	error
`E220`	Front Panel communication UART input overrun	Front Panel UART receives data while buffer still processing	error
`E221`	Front Panel communication UART framing error	Front Panel UART data frame format violation detected	error
`E222`	Front Panel communication UART parity error	Front Panel UART parity check validation failure	error
`E223`	Front Panel firmware input buffer overrun	Front Panel firmware receives data faster than processed	error
`E3`	Checksum in Cal Non-volatile ROM	Calibration ROM checksum validation failure during self-test	critical
`E4`	Checksum in State Non-volatile ROM	State ROM checksum validation failure during self-test	critical
`E5`	Checksum in RST Non-volatile ROM	Reset ROM checksum validation failure during self-test	critical
`E80`	Digital I/O test failed	SEC_PCLR written low and high; not read back correctly through Xilinx	critical

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.