Alesis 3630 Compressor
Today, something unusual for me, as far as my repairs are concerned. First, it is not a synthesizer, and second, it is an analog unit, which I normally do not repair. An Alesis 3630 compressor.
The problem with this unit was that it would randomly “freeze” (even though the equipment does not have any microprocessor in it). During this, almost all of the LED level indicators would light up, while the compressor itself would practically stop responding to the input signal. After looking at the schematic, I immediately suspected a possible culprit. It was the unfortunate power supply circuit used in Alesis equipment from this period: a double voltage doubler (for the +15 V and -15 V rails), powered by an external 9 V power supply. It is a very “fussy” and unreliable solution.
I did a complete recap of the compressor, replacing all 44 electrolytic capacitors, and I also replaced the rectifier diodes in the voltage doubler circuit. I could have replaced only the capacitors in the power supply section, but I decided that equipment this old deserved a complete recap.
I also replaced two rotary potentiometers because the knobs were so firmly stuck that they damaged the potentiometers when I tried to remove them. The knobs came off together with the shafts. Fortunately, these were very cheap potentiometers. The unit is now fully working again, and I gained some more experience repairing analog equipment.
