[kevinaston1]

Sorry, I have no service data for a Studiologic SL-880; I doubt it even exits. Since the demise of the Italian keyboard industries in the 70’s the manufacturers around the Castelfidardo region have had a very tough existence.

By far, the greatest number of faults are power supply related. Ensure that any regulators have at least 2.5V higher on the input than its regulator voltage; otherwise they are prone to dropping out.

Check for oscillation and ripple with the scope set to a.c. and the gain turned up – difficult to see 20mV of noise on top of a 5V trace.

The processor (CPU) will be the biggest IC on the board. Rather than trying to identify the clock oscillator pins, look for the crystal which will be mounted close by. If you scope this, you have a direct reading of the clock frequency. Look on the case of the crystal, and it will give a clue as to its operating frequency. It should be a nice clean signal, with no jitter, and at the quoted frequency.

Be careful. Sometimes, the loading of the scope probe can stall a crystal. If this happens, switch your probe to divide by 10 (if it is switchable), turn up the Y gain to compensate.

Pin 4 of the MIDI out socket is the 5V bias supply to the optocoupler in the next MIDI item in the chain. You will see a small variation here during data transmission, but not much. Look at pin 5 to see the actual data.

To see a clear data chain, keep hitting and releasing a key; you then have a nice constant note on, pitch and note off data stream to look at.

Alternatively, if you have MIDI software which includes a decoded MIDI event page, set the software to record and look at the MIDI events as they roll on; you will soon notice any event other than note data.

Also never forget the technician’s friend to locate intermittent faults – heat and cold. Gentle heat from a hairdryer will bring 99% of faults on. Once you have a set of suspect components, the application of a freezer spray will remove the fault instantly, showing the culprit(s).

Kevin