The Ultimate questions on Linux, the Universe, and Everything

In the previous article , I covered the functionality and issues of the D400-007D 400V DC linear power supply by Oltronix.  In this second part, I'll describe the repairs and improvements carried out and also provide a link to the complete KiCad PCB project. Main high-voltage board  On the main high voltage board, the two main filter capacitors (C80, C81) were replaced with two 500 V, 100 µF capacitors. Although the original capacitors were still within specification, they were replaced to ensure reliable operation under modern mains conditions. Equivalent axial capacitors are expensive, so two more cost-effective radial capacitors were used (high-quality 105 °C types).  Two mounting holes were drilled in the PCB, and the capacitors were secured using cable ties. Jumper wires were then used to connect them to the original capacitor pads. The increased capacitance is not an issue due to the high resistance of the transformer secondary. It does not introduce significan...

Update, there is now also a part 2 .  This is another 1960s-era laboratory power supply from Oltronix. This article provides an overview of the design and highlights key considerations when repairing or restoring the unit. To ensure reliable operation on modern mains voltages, several components require upgrading or replacement. Below is a screenshot from the original LABPAC 30-series product presentation:           Front view.      Rear view with the EL34 series pass element visible.

Repairing an Oltronix B602D Power Supply This is a repair and maintenance description of a 1970s linear bench power supply: the Oltronix LABPAC B602D. I bought this unit from a scrap dealer and managed to negotiate a good price. It is a classic 1970s linear laboratory power supply with two channels: 0–30 V at 1.4 A and 0–60 V at 0.7 A. The channels are fully independent, with an isolation voltage to each other and to chassis of ±500 V DC (according to the manual). It even features a “digital” voltage display. Oltronix was a Swedish company that produced high-end laboratory equipment; parts of the company still exist today and are based in the Netherlands.  There is also a similar three-channel model, the B603D, which includes an additional 6 V supply.   I opened the unit and cleaned out some dust before powering it on. “Take it apart,” as Dave Jones says. Internally, it looked reasonably good. On power-up, the 0–30 V channel worked fine, but the 0–60 V channel did not. I then...

When soldering, you sometimes need a third hand keeping things in place. I got this idea from the eevblog forum ( https://www.eevblog.com/forum/reviews/a-3rd-hand-that-actually-works!/ ) and the excellent blog post here: https://www.engineerable.com/single-post/diy-the-best-helping-hands-for-electronics-soldering-pcb-work-jewelry The thing is, that cheap "helping hands" or "third hands" frankly sucks.  I'm thinking on the ones that look like this:  I've used these ones and the mechanism is limited and the crocodile clips are annoying and don't grip well. You can improve them slightly by adding some heat shrink tube on the teeth. I do use also other kind of tools, e.g. a regular vice: This is an excellent vice for the price. The model is  RÖHM 863421 , and it's perfect for small hobby projects including drilling and cutting.  I also have this holder for PCBs. It works OK:   Now I did have one of these magnetic holder stands for dial indicators. But I ...

I have this old digital caliper that is rarely used, because the battery is always empty. The issue with these calipers is that they don't have any on-off switch, so they are constantly draining the battery. Basically they only switch off the display. I don't know whether newer calipers also suffer from this problem. It's a shame, because this is a good old caliper. Newer ones look and feel like they are made cheaper. I've seen people on the Internet adding various kinds of switches to their calipers, even external batteries(!), but I've not seen a good solution. The issue has been finding a small enough switch that doesn't interfere with the usage of the caliper. I was lucky with this one, because I found a switch that was a perfect fit without any modification to the caliper. Here is my solution: I used a small DIP switch: DIP switch dimensions are 10 mm x 6.5 mm x 5.5 mm (length x width x height).  On this caliper, there is a small lid on the top side above t...

    This is a DIY capacitor reference box that can be used to verify and compare multimeters. It's not a metrology grade reference, but has capacitors with better tolerances than what is typically available in electronic circuits. It's still relatively cheap. For better results, a calibrated instrument should be used to check capacitor values. The reference box contains capacitors in the range from 10 pF to 10 mF.  It should be said from the beginning, that capacitances below 100 pF is hard to use in a box like this, due to stray capacitances in wires, terminals and the box itself. This is discussed later below. Capacitor types There are many different types of capacitors with different dielectric and specifications. Not all of them have a stable capacitance with regards to temperature, age, voltage, DC bias voltage and other factors. The most stable ones are in general film capacitors, where polystyrene and polypropylene dielectric materials are considered best. Of small...