E-mu e64
Another E-mu sampler has arrived at my workshop. This time, it’s an E-mu E64.
The fault manifested itself as a complete lack of audio output (both the main OUTPUT connections and the headphone output), as well as a lack of backlighting on the graphic LCD display. My first suspicion was a faulty power supply and a missing supply voltage. Other possibilities included failed electrolytic capacitors in the audio circuitry or a malfunction of the muting circuit.
After an initial inspection, it turned out that all the voltages supplied by the very solidly designed power supply were correct. Interestingly, the muting circuit, whose failure is often responsible for a lack of audio output, was also working properly. The actual cause of the problem was something entirely different.
The unit uses transistors to switch the power supply voltages feeding the audio board. They are activated with a slight delay after the sampler is powered on (via an RC circuit), supplying the board with +5 V and -5 V, which are essential for the proper operation of the operational amplifiers and other components in the audio signal path.
This is quite an unusual design choice, considering that the muting circuit already takes care of silencing the audio signal during startup. It’s difficult for me to determine exactly what the designers had in mind, especially since E-mu does not provide service documentation for this model. One can only assume that this additional power supply switching had a specific engineering purpose. I have to admit that E-mu has a reputation for designing very well-thought-out equipment.
As is often the case with older equipment, the problem turned out to be caused by one of the electrolytic capacitors. This time, it was a tantalum capacitor located in the RC circuit, and there are quite a few of them on the audio board. Its failure prevented the +5 V supply voltage from reaching the audio circuitry, resulting in a complete loss of sound.
In addition to the faulty capacitor, I also replaced the remaining electrolytic and tantalum capacitors on the audio board. Considering the age of the unit, I felt that replacing them all was a sensible precaution.
The non-functional display backlight was a separate issue. In this case, the culprit was a hybrid DC/AC converter responsible for generating the voltage exceeding 100 V required to power the LCD backlight. Since the original converter is virtually impossible to obtain, I used a universal replacement module costing just over $2. I adapted it to the unit, successfully restoring the display backlight.
With these repairs completed, the E-mu E64 sampler was fully operational again.
