The sound probably wont be as regular and you might be able to smell ozone in that case. Maybe a mounting can be tightened, maybe there is nothing to do about it.īuzzing can also be caused by arcing due to fx a loose connection on the primary side, which is worse (from a safety standpoint). You can maybe feel the vibrations if you put your hand on it. First of all, if you have any reason at all to suspect the PSU, it's not advisable to connect it to the machine until further tests.īuzzing could be just due to 50hz vibrations corresponding to the line frequency in the mounting or inside the transformer itself and is not necessarily critical, albeit annoying. Welcome to the Retrocomputing Stack Exchange. If you do bother, however, you can replace the voltage regulator by a switching one, like a Traco No reason to bother, it will simply transform the rest into heat. The linear regulator in the ZX Spectrum can easily "eat" the 12.5Volts. Make sure you get a product that is certified as an isolating lacquer spray for electric components - don't use any old paint you might have! This is not quaranteed to help, but might (glues the single components of the transformer together and stops the vibrations). If that doesn't help either, you can try a generous spraying of the sheet packet and windings of the transformer with special isolating lacquer It's normally held together with long screws you might need to tighten. If this doesn't help, check the transformer. In this case, check for loose parts (espcially the PCB on top of the transformer) and try and fasten them.
The other (more likely one) is just a mechanical annoyance: The metal sheets or the copper windings (or some other parts) in the transformer have losened over time and start vibrating with the AC frequency. This case is dangerous and a fire and electrical hazard!
It's unlikely you could have measured a stable output voltage in this case, but it's still worth checking carefully. One (luckily the unlikely one) is electrical current jumping an air gap in the PSU causing intermittent shorts through an arc.
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