Archive for Equipment Repair

Teardown, Repair and Analysis of an Agilent 8449B 1.0 – 26.5GHz Microwave Preamplifier

In this episode Shahriar analyzes the failure of two Agilent 8449B Preamplifiers. These units should provide up to 30dBm of gain from 1.0GHz to 26.5GHz intended for use as a preamplifier. Both amplifiers test positive for power supply voltages and operation. After removing the interface cables from the amplifier module to the front panel, it becomes clear that mechanical shock has caused damage to the front panel connectors. Replacement cables and connectors are used to correct the problem.

Teardown, Repair and Analysis of an Agilent 4338B (10uΩ – 100kΩ) Milliohmmeter

In this episode Shahriar repairs an Agilent 4338B milliohmmeter. This instrument is capable of measuring extremely small resistances down to 10uΩ while maintaining a DUT voltage of less than 20mV. The instrument powers on with the message ADC Failure. Investigation reveals that the instrument uses an obsolete ADC which must be removed from the board in order to reverse engineer its operation. While the ADC turns out to be functional, a PAL device which controls the ADC timing is faulty. A new device is salvaged from a donor board to complete the repair. The instrument is then used to measure several small known resistances.

Teardown, Repair and Experiments with an Agilent E4981A High-Speed Capacitance Meter

In this episode Shahriar investigates an Agilent E4981A high-speed capacitance meter which fails self-test during startup. The instrument reports a series of errors associated with the CPU board. The teardown reveals a multi-board construction where the main analog assembly employs an FPGA for control and interface to the main CPU board. The unit has a disconnected ribbon cable between the analog board and the main CPU assembly. After correcting the problem the instrument completes self-test without errors.

After the repair the unit is used to measure several known capacitors for functionality verification. Finally the instrument is used to measure a hand-made parallel plate capacitor. The capacitor can accept various types of dielectric material whose impact is studied.

Teardown & Repair of an Agilent E4440A 3Hz – 26.5GHz PSA Spectrum Analyzer

In this episode Shahriar takes a close look at a defective Agilent E4440A spectrum analyzer. Initial analysis reveals that the startup errors are caused by a defective pre-amplifier module. During initial alignment and calibration, the defective microwave relays inside the pre-amplifier module fail insertion loss specifications and cause alignment failures.

Unfortunately, the relays are not repairable and must be replaced. Two new relays are purchased and replacement clears all alignment issues. The main motherboard battery has also failed; a replacement battery corrects any time and date keeping errors. The repaired instrument is cycled through several alignment procedures without any problems. The performance of the unit is verified by examining the DANL of the instrument with and without the pre-amplifier activated.

Teardown, Repair & Upgrade of an Agilent 3458A 8.5 Digit Digital Multimeter

In this episode Shahriar repairs and upgrades an Agilent 3458A 8.5 Digit Multimeter. The instrument has been kindly donated by AllTest Instruments Inc. You can access their website here, as well as their eBay store, Bonanza store and TestUnlimited hub. AllTest provides the following:

  • Massive inventory of test and measurement equipment with over 20,000 units to chose from.
  • Full service general laboratory where repairs, refurbishment, and testing are carried out.
  • An additional NIST traceable metrology laboratory with extensive T&M capabilities where OEM grade calibrations are performed.
  • 5% discount on any purchase when The Signal Path Blog is mentioned for first time customers with limit one per customer.

The 3458A unit fails startup conditions with several errors. After close inspection of the boards, the initial problem points to a poorly plugged in fiber-optic cable. After this fix, the unit still fails ACAL on the AC Board. The unit’s NVRAM modules all have to be replaced. During this process the memory of the unit is also upgraded and the firmware is updated to the latest available version. After analysis of the schematics the problem is traced to a damaged JFET input operational amplifier on the attenuator flatness calibrator unit. The replacement allows the unit to pass all self-test and ACAL calibration. The instrument is then NIST calibrated by AllTest Instruments and shows excellent performance when compared with various multimeters in the lab.

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