Author: Sebastian Harnisch

  • Lenovo ThinkCentre M720q: Upgrade

    Lenovo ThinkCentre M720q: Upgrade

    In order to be able to look at schematics etc. during repair and soldering sessions I recommissioned my old monitor months ago and connected it to my main PC that sits on a seperate bench. That solution kind of worked, but going back and forth between different monitors on different benches was a bit impractical.…

  • Programmable Power Resistor: Final Product

    Programmable Power Resistor: Final Product

    Although the Programmable Power Resistor re-uses some components, many design ideas and a good portion of the software of the Programmable Decade Resistor (Programmable Precision Resistor), there were many changes and also some improvements regarding some aspects of the mechanical construction and the code. Features and specs So now it’s time to present the feature…

  • Programmable Power Resistor: System Design

    Programmable Power Resistor: System Design

    The Programmable Power Resistor consists of two large boards: The User Interface and Controller Board and the Relay and Interface Board. Because of the use of relays that isolate the input from the circuits, all circuits can be and therefore are earth-referenced. The only microcontroller, a STM32G441RBT6, is located on the User Interface and Controller…

  • Agilent 6632B Teardown & Transient Response

    Agilent 6632B Teardown & Transient Response

    The HP/Agilent 6632B is a remarkable power supply. There are some similarities with the mobile communication DC source 66309D I “repaired” recently: The 6632B is optimized for a fast transient response and it has a low current range too. But the circuit and its properties differ significantly. One important aspect: Where the 66309D only has…

  • Programmable Power Resistor: Topology (2)

    Programmable Power Resistor: Topology (2)

    In the last post we had a look at a simple topology that allows us to switch between a series and a parallel connection of two resistors: Now we’ll nest these structures so that we have four resistors: The interesting part here is that two of the four switch states of the outer structure don’t…

  • Programmable Power Resistor: Topology (1)

    Programmable Power Resistor: Topology (1)

    For the performance checks and calibration of my Agilent 6811B AC Power Source/Analyzer (375VA) I need a 20 Ohm resistor with a ton of power handling capability. The original plan was to mount 8 wire wound 50W resistors on a heat sink and be done with it. Then I thought: Why not reuse all the…

  • Agilent 66309D: Repair

    Agilent 66309D: Repair

    A few days ago I got my hands on a faulty Agilent 66309D Mobile Communication DC Source. To be honest, I don’t think I need it, but it was pretty cheap and I was looking for something to either repair or potentially salvage the case of. The Mobile Communication DC Source is a specialized power…

  • Programmable Decade Resistor: Cost

    Programmable Decade Resistor: Cost

    I didn’t really think about the BOM cost of my programmable decade resistor until I was asked. Then I also wanted to know. It is fairly difficult to put a number to what I paid, since I had a lot of components left from other projects that I could use. This includes not only cheap…

  • Logitech M310: Mouse Button Repair

    Logitech M310: Mouse Button Repair

    For some time it became more and more difficult to get a click out of the mouse wheel switch of my old Logitech M310 mouse – inconvenient in programs like KiCAD. I also have a newer and “better” M705 mouse, however, using this one seemed to increase fatigue compared with the old M310. The mouse…

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