Yamaha SPX-90
This is already the second Yamaha processor of this type in my workshop. This time it’s the so-called “brick” Admittedly, after powering it on, half of the input signal level bargraph would light up (honestly, I’m not sure how it even managed to do that), but that was all this processor was capable of.
It turned out that the built-in switching power supply had suffered serious damage. Key semiconductors had burned out, as well as the high-power resistors feeding the main electrolytic capacitor of the input rectifier (68 µF/400 V). Since I’m not a specialist in DC/DC converters, I was close to giving up and replacing the original PSU with a universal module (+/-18 V and +5 V). However, thanks to the persistence of both the owner and myself, the repair of the original power supply was ultimately successful.
The main power transistor, the driver transistor, two rectifier diodes, power resistors, and a full set of electrolytic capacitors were replaced. Of course, it wasn’t entirely certain whether the failing power supply had also damaged the main board, but fortunately it turned out to be fully functional. Additionally, the worn-out CR2032 battery backing up the RAM was replaced, and a proper holder was installed to make future replacements easier. As a result, the effects processor has been fully restored.
