Teardown and repair of an Agilent E3632A DC power supply

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Teardown and repair of an Agilent E3632A DC power supply from The Signal Path:

In this episode Shahriar & Rosanah investigate an Agilent power supply which does not appear to power on. It can be quickly observed that the fuse has failed on the unit. Using an isolation transformer a small amount of AC voltage is applied to the unit after the fuse replacement. It is clear that a short is present somewhere in the instrument since even at 10V AC the instrument consumes more than 1A.

See the full post at thesignalpath.com.

Check out the video after the break.

Build your own testing/programming jig

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Sjaak has published a new build:

Inspired by an old article from sparkfun and some tests I conducted myself I came up with a PCB that holds the pogopinholders and an lasercut acrylic fixture for the PCB on top. Using the dirt(y)cheap services from dirtypcbs.com the cost for this jig, including pogopins and their holders is about 45 USD. As an advantage you receive 5 lasercut acrylic and 10 PCBS which allows you to make 3-4 jigs in total!
To design the PCB that holds the pogopins I started with a 10×10 PCB with M3 mounting holes and imported the to be programmed PCB (File, Import, Eagle drawing) and place this in the centre (not mandatory, but looks prettier).

See the full post at smdprutser.nl.

DirtyPCBs adds full range of steel and framed stencils

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Stencils for solder paste and red glue are now available in a bunch of standard sizes for solder paste/red glue dispensers. You can choose from all the options offered by our favorite stencil maker:

  • Purposes: Solder paste for surface mount component reflow process. Red glue for two-sided or through hole board wave soldering process
  • Alignment: quarter points for automated dispensers, and through hole for hand application
  • Polishing process: hand sanded (for most stuff) or electrolytic (for BGA footprints)
  • Engineering options: your paste layer (untouched), auto (China standard), auto with approval by PDF

We’ve been playing with the Neoden4 pick and place machine in a mini production line and needed a better way to order stencils with advanced options. Give us a shout if we missed any options you need!

DirtyPCBs site update with encrypted https connections

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DirtyPCBs.com now supports secure, encrypted access with https://DirtyPCBs.com. We used a free certificate from Let’s Encrypt and the process was almost painless. You’ll need to add the ‘s’ to the address manually to access the secure version of the site.

Https may become the default eventually. It’s trendy to force everyone onto https these days, but China targets https traffic for slowdowns and blocking. The Shenzhen office has a much better experience using the non-encrypted http version so we’ll keep it around.

WiFi TFT touch LCD weather station with ESP8266

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Erich Styger built this ESP8266 WiFi weather station with touch LCD and wrote a post on his blog detailing its assembly:

After the “WiFi OLED Mini Weather Station with ESP8266“, here is another one: this time with Touch LCD :-)  In the previous article (“WiFi OLED Mini Weather Station with ESP8266“) I have used the OLED kit from blog.squix.org. And as promised, this time it is about the “ESP8266 WiFi Color Display Kit”

Project info at MCU on Eclipse. Code is available on GitHub.

App note: Using trench technology MOSFETs in hot swap applications

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Safely use trench MOSFETs on hot swap application by determining its operation within its SOA in a limited time, app note from International Rectifier. Link here (PDF)

Hot Swap circuits are used to allow for “Hot Plugging” of circuit boards into back planes. The applications that require such functionality are mission critical, such as servers and communications equipment that must operate continuously. These circuit boards are usually employed in a rack mount system which consists of an array of boards that cannot be powered down. Thus hot swapping allows for a bad board in the array to be replaced without powering down the entire system.

In essence the Hot Swap circuit, which is between the board input rail and the rest of the board’s circuitry, is an inrush current limiter that allows for charging of the bulk capacitance in a controlled manner. Also faults, such as over current and overvoltage are managed by Hot Swap circuits.

App note: Class D audio amplifier performance relationship to MOSFET parameters

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Application note from International Rectifier on MOSFET paremeters to consider when designing a Class D audio amplifier. Link here (PDF)

Class D audio amplifier is a switching amplifier that consists in a pulse width modulator (with switching frequency in order of several hundred kHz), a power bridge circuit and a low pass filter. This type of amplifier has demonstrated to have a very good performance. These include power efficiencies over 90%, THD under 0.01%, and low EMI noise levels that can be achieved with a good amplifier design.

Key factors to achieve high performance levels in the amplifier are the switches in power bridge circuit. Power losses, delay times, and voltage and current transient spikes should be minimized as much as possible in these switches in order to improve amplifier performance. Therefore, switches with low voltage drop, fast on and off switching times and low parasitic inductance are needed in this amplifier.

MOSFET have proved to be the best switch option for this amplifier because of its switching speed. It is a majority carrier device, its switching times are faster in comparison with other devices such as IGBT or BJT, resulting in better amplifier efficiency and linearity.

Network cable tester

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Dilshan Jayakody writes, “This is an automatic Cat6 / Cat5 network cable tester designed using NE555 timer and 4017 decade counters. This unit test all 8 wire lines of twisted pair network cable and indicate pass/fail status with single LED. We design this unit to test network connectivity issues in Cat6 / Cat5 cable systems and it is capable to check both crossover and straight-through type network cables.”

More info on his blog here.

DIY ISA game control adapter with parallel IO

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Dr. Scott Baker has published a new build:

My Xi 8088 homebuilt PC is running a little short on slots, so I wanted to combine the functions of a game control adapter and an 8255 PIO board. Two functions in one slot. As to why one wants each of these things:

  • A game control adapter is used to interface to PC joysticks. These are the old-style analog joysticks with the 15-pin connectors.
  • An 8255 board is a general purpose interfacing board, providing 24 bits of digital IO that can be configured as inputs, outputs, or a mix of both. This is not in and of itself a “parallel port”, but could probably be used to implement one.

See the full post on his blog.