This time a fairly simple instrument landed on my workbench, although it must be said that despite using Yamaha synthesis, it also features a digital delay line (DDL), which significantly enriches the sound. However, due to its design it is also the source of many problems (it uses more than 30 electrolytic capacitors, including some unusual values such as 0.22 µF and 0.47 µF).

So what was wrong with this instrument? It produced no sound at all. As always, the first place to start is the power supply— in this case a symmetrical ±15 V supply providing voltages for the analog section. It turned out that these voltages were missing, and the cause of the failure was two blown fuses located before the bridge rectifier in the symmetrical supply. After replacing the fuses, the instrument immediately came back to life.

Of course, that only fixes the symptom. The next step was to determine why the 500 mA fuses had blown, since the current I measured for the analog section (mainly operational amplifiers) was only 32 mA, which is perfectly normal. In fact, I don’t really know the exact reason. At the moment the instrument draws the correct current, and there could have been various causes for the blown fuses. It is also possible that someone previously caused a short circuit in the power supply.

Nevertheless, nothing currently indicates any malfunction in the analog section. The instrument plays cleanly and shows no problems. As a result, this turned out to be the fastest and cheapest repair so far.

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