Archive for February 20, 2017

Teardown & Repair of a BK Precision 879B Handheld LCR Meter

In this short episode Shahriar repairs a more affordable instrument! This BK Precision LCR meter does not power up despite looking almost new. The teardown of the unit reveals several damaged components. Without any schematic and obscure part numbers some circuit configurations have to be reverse engineered. One of the main failed components is a TI DC-DC converter IC whose datahseet is examined during the repair.

The damaged components are replaced and the unit powers on normally. The performance of the instrument is verified using a HP LCR meter. The demonstrated Soldering Iron Stand can be found here.

Teardown & Analysis of Microwave (26.5GHz) Electro-Mechanical Step Attenuators

In this short episode Shahriar takes a close look at a pair of Hewlett Packard microwave electro-mechanical step attenuators operating up to 26.5GHz. Mechanical attenuators offer excellent repeatability, low insertion loss and nearly limitless linearity. The teardown reveals that the construction of both modules is very similar on the microwave path. In fact, the lower-frequency model still uses the same attenuator components. The newer model employs electronic control circuity while the older generation attenuator uses purely mechanically controlled DC path. Both models use a solenoid style actuators for step attenuation control.

DeoxIT Challenge & Restoration of a Precision Decade Resistor Box

In this short episode Shahriar attempts to revive a high-accuracy decade resistance box using the famous DeoxIT cleaning and restoration products from CAIG Laboratories. The DeoxIT D-Series products are particularly aimed at metal-metal contacts which have suffered oxidization and can provide a low-resistance repeatable contact after application.

The existing decade resistance box shows inconsistent measurements and intermittent contacts prior to the DeoxIT application. After spraying all contacts the instrument is significantly improved with repeatable and accurate resistance measurements. DeoxIT can be purchased from a variety of suppliers and vendors including Amazon.

Teardown & Analysis of an Anritsu MN9610B Variable Optical Attenuator

In this short episode Shahriar takes a detailed look at an Anritsu variable optical attenuator operating in the L- and C-Bands. The mechanical attenuator is defective and provides an opportunity for complete disassembly and examination of the free-space optics, mechanical components and electronics.

The electronics drive a pair of DC motors with potentiometer decoders in feedback along with operational amplifiers and a DAC. This allows the microprocessor to set the exact position of the motors based on calibrated values stored on EPROM. The free-space optics consists of two back-to-back disks with radial metal coatings. Depending on the position of each wheel, the coating limits the transmission of the light through the wheel causing attenuation. The entire housing is hermetically sealed to prevent degradation of the disks.

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