Test equipment and power supplies

Agilent E4350B: troubleshooting and error codes

The ServiceForge knowledge base holds 11 documented symptoms for the Agilent E4350B, with 31 ranked causes, 22 diagnostic checks with test points and expected values, and 26 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 held low high voltage

Supply output is low and PROT annunciator is not on

Ranked causes

1. Secondary bias or reference voltage out of spec (common)
2. Rail voltages incorrect (common)
3. Primary circuit failure (power transformer, rectifiers, filter capacitors) (occasional)
4. CV/CC OR gate diodes conducting (occasional)
5. A1D411 diode conducting (occasional)
6. VMon amplifier A1U401 defective (rare)
7. CV comparator A1U408 defective (rare)

First check

Measure secondary bias and reference voltages

Test point: TP 9 through 12
Expected: Per Table 6-3
Tools: DMM

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

Display does not turn on

No display output visible; fan may or may not be running

Ranked causes

1. AC input fault or line fuse open (common)
2. A3 front panel board defective (occasional)
3. A3 microprocessor or ROM defective (rare)
4. LCD or cable W19 defective (occasional)

First check

Is display on?

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

Fan does not run caution

Supply is powered but cooling fan does not operate

Ranked causes

1. AC bias voltage fault or fan cable disconnected (common)
2. Fan speed control circuit defective (occasional)
3. Fuses F700, F701 open or capacitor/resistor fault (occasional)

First check

Measure voltage at A1Q770 heatsink (TP 12) vs common (TP 9)

Expected: +24V

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

Output held high high voltage

Supply output is high and cannot be reduced to commanded voltage; output regulation failure

Ranked causes

1. Secondary bias or reference voltage incorrect (common)
2. CV feedback control path faulty (common)
3. Tunnel board defective (occasional)

First check

Turn supply off and disable overvoltage circuit

Test point: A1U410 pins 1&2, A1R447
Expected: Overvoltage circuit disabled for testing

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

Overvoltage condition triggered at turn-on caution

OV protection activates immediately when power supply is turned on, preventing normal operation

Ranked causes

1. Output voltage exceeds OV setting at start-up (common)
2. OV control circuit latch transistor defective (occasional)
3. Output momentarily exceeds voltage setting (occasional)

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

No output voltage or current despite enabling

Output remains disabled or at zero volts; supply does not respond to programming commands

Ranked causes

1. GPIB interface fault (common)
2. Primary interface or front panel control circuit defective (occasional)

First check

Connect GPIB controller; program supply to full scale voltage and current; verify it accepts commands

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

Output current not within specification caution

Programmed output current does not meet expected value; may read approximately correct but outside tolerance

Ranked causes

1. Current readback circuit defective (common)
2. Cable from A1 to A5 DSP board disconnected or defective (occasional)

First check

Connect short across output; program full scale voltage and current; measure with external ammeter

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

Output voltage held at zero or low value

Output voltage cannot be programmed above zero or remains at reduced value

Ranked causes

1. Output shorted or current-limited (common)
2. Voltage monitor circuit defective (occasional)

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

Output voltage not within specification caution

Programmed output voltage does not meet expected value; may read approximately correct but outside tolerance

Ranked causes

1. Voltage readback circuit defective (common)
2. Cable from A1 to A5 DSP board disconnected or defective (occasional)

First check

Program full scale voltage and current; check output voltage with DMM

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

Overvoltage protection will not trigger caution

OV protection does not function; supply does not enter OV condition when programmed

Ranked causes

1. OV circuit comparator or switch defective (common)
2. OV feedback network resistors or capacitor defective (occasional)

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

Output current held at zero or low value

Output current cannot be programmed above zero or remains at reduced value despite voltage enabled

Ranked causes

1. Current monitor circuit defective (common)

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

Error codes

Code	Meaning	Trigger	Severity
`E1`	Front panel RAM test failed	Microprocessor detects RAM error during self-test	error
`E10`	Secondary interface 5V readback test failed	Voltage measurement error on 5V supply during self-test	error
`E11`	Ambient temperature readback test failed	Temperature sensor or measurement circuit error during self-test	error
`E12`	CV or CC DAC test failed	Digital-to-analog converter error during self-test	error
`E2`	Front panel ROM test failed	Microprocessor detects ROM error during self-test	error
`E3`	Front panel EEPROM checksum failed	Checksum error detected during self-test	error
`E30`	Secondary interface DAC test failed	Digital-to-analog converter error on A5 board	error
`E31`	Secondary interface DAC test failed	Digital-to-analog converter error on A5 board	error
`E32`	Secondary interface DAC test failed	Digital-to-analog converter error on A5 board	error
`E4`	Primary interface external RAM test failed	RAM error detected on A2 GPIB board during self-test	error
`E45`	Secondary interface I/O test failed	Input/output circuit error on A5 board	error
`E46`	Secondary interface nonvolatile RAM test failed	NVRAM error on A5 board during self-test	error
`E5`	Primary interface internal RAM test failed	RAM error detected on A2 GPIB board	error
`E6`	Primary interface ROM test failed	ROM error detected on A2 GPIB board	error
`E7`	GPIB interface test failed	GPIB communication error during self-test	error
`E8`	Secondary interface RAM test failed	RAM error detected on A5 DSP board	error
`E9`	Secondary interface ROM test failed	ROM error detected on A5 DSP board	error
`EE WRITE ERR`	EEPROM write failure on front panel board	EEPROM programming failed	error
`SBUF FULL`	Serial buffer full on GPIB board	Serial buffer capacity exceeded	warning
`SBUF OVERRUN`	Serial buffer overrun on GPIB board	Serial buffer received more data than capacity	warning
`SERIAL DOWN`	Serial data line failure on DSP board	Serial communication failure on secondary interface	error
`SERIAL TIMEOUT`	Serial data line failure on GPIB board	Serial communication timeout during self-test	error
`STK OVERFLOW`	Stack overflow failure on DSP board	Microprocessor stack exceeded during execution	error
`UART FRAMING`	UART framing error on GPIB board	Invalid framing detected in serial communication	error
`UART OVERRUN`	UART overrun error on GPIB board	Serial data received faster than processed	error
`UART PARITY`	UART parity error on GPIB board	Parity bit mismatch during serial communication	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.