Repairs

I’ve recently been restoring vintage Hi-Fi equipment, focusing on Technics preamps, integrated amplifiers, and power amps. My first project in this series is a Technics SU-8080 integrated amplifier, which arrived in decent cosmetic condition (and with printed schematics!). However, it was covered in dust like I’d never seen before and suffered from frequent channel dropouts, rendering it unusable. ❗ The elevated voltages inside this amplifier can cause damage, severe injury, and death. If you are not authorized or qualified to work on such equipment, do not do it. If you follow along, you do so at your own risk. ...

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 large degree there are some design aspects that are a bit more objective. What I particularly like about the SU-VX 700 is mostly related to its simplicity and repairability: ...

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 supply. It not only has an improved transient response, but also a few other features not found on standard power supplies (e. g. E363x, E364x). The list for the Agilent 66309D includes (not necessarily exhaustive): ...

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 wheel switch SW3 (center) is one of the cheap through-hole tactile switches used everywhere - and sure enough, I didn’t even have to order a replacement. After a tiny bit of disassembly, desoldering, replacing old switch with a new 10 cent one, soldering and re-assembly it works perfectly again. Certainly cheaper and more fun than buying a new 30 to 40 EUR mouse. Why didn’t I do that sooner? ...

The other day I noticed an issue with one of my Agilent 34401A’s: I measured a constant DC voltage and after a few minutes the measured value would start dropping and become unstable. Then I got curious and checked the two-wire resistance mode. Same story, maybe worse. A word of caution: High voltages found inside the DMM can cause damage, severe injury or death. If you are not authorized or qualified to work on such devices, don’t do it. I don’t take any responsibility for actions you take or the results of these actions. You do everything at your own risk. ...

For engineers analog oscilloscopes are a bit like vinyls and tube amplifiers: Most don’t use them anymore, but if they see one, they think: Nice! And are happy that they don’t have to deal with them on a daily basis ;) However, I bought a Tektronix 465B with a faulty second channel, just to repair it. For this one, I made a quick YouTube video. ❗ Caution High voltages found inside of analog oscilloscope can cause damage, severe injury or death. If you are not authorized or qualified to work on such devices, don’t do it. I don’t take any responsibility for actions you take or the results of these actions. You do everything at your own risk. ...

I recently scored two Fluke 175 multimeters that were sold on ebay as a set waiting for repair. According to the seller, the first multimeter was fully functional except for the beeper. The second meter had a strange error rendering it unusable, but came with a working beeper. The sellers suggestion then was to transfer the known-good beeper to the first meter. ❗ Caution Multimeters can be used to measure sources that can cause damage, serious injury or death. If you are not authorized or qualified to work on such devices, don’t do it. I don’t take any responsibility for actions you take or the results of these actions. You do everything at your own risk. ...