• Lenovo ThinkCentre M920q – M920x conversion

    Lenovo ThinkCentre M920q – M920x conversion

    There are many advantages of the 1l mini PCs for home server applications: Obviously they are very compact, but more interestingly: The idle power consumption can be almost as low as current Raspberry Pi 5s acchieve, i. e. 5-6W*, all while avoiding many of their limitations**. In many cases the low power consumption is associated…

  • Make-shift 19″ rack: Easy to build, even easier to overload

    Make-shift 19″ rack: Easy to build, even easier to overload

    For quite some time I was looking for a rack to mount my 19″ HP/Agilent gear in. I haven’t found a single rack that meets all my requirements. Most are too big, too small, too flimsy, too heavy, poorly made, too expensive, lack cooling … or are simply made for a different purpose. Since I…

  • Technics SU-VX 700: Teardown & Service

    Technics SU-VX 700: Teardown & Service

    The Technics SU-VX 700 is an integrated audio amplifier from the early nineties. It delivers 2x 90W into 8 Ohms and is specified with a THD of 0.007% (20Hz .. 20kHz, rated power). In my opinion it is one of the better Technics amplifiers. Whereas the sound of an amp is always subjective to a…

  • 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…

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