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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...

Building a 1 W, 0.5 % decade resistance The seven decade programmable resistor - my variant. Gerry Sweeney designed and built a really neat little SMD decade resistance board a few years ago. He still offers it for sale, already assembled, check it out! You can find it here: https://gerrysweeney.com/seven-decade-programmable-resistor-a-low-cost-solution/ Screenshot from Gerry Sweeney's site. Gerry Sweeney's design is cheap, simple and uses 1 % and 0.5 W resistors in the 1210 size (metric: 3225). Why build my own? I decided to build a similar board, but to use at least 0.5 % tolerance, better temperature coefficient and higher power resistors. This was more of an exercise to see what kind of SMD resistors are available and if it is possible to design it for higher power output and better tolerance at the same time. The answer is that it is, but it comes at a cost.  What kind of resistors? I tried to use 1206 size (metric: 3216) resistors where possible. They are a bit smaller an...