Korg Forums

[EamonnS]

This problem first occurred 18 months ago. I sent it to a Korg engineer, he repaired it for £500!! Apparently the Digital to Analogue board had failed. I brought it home, played it a few times, then developed a problem with my hand which meant that I could not play the Kronos until now. So, I plugged the keyboard in, booted it up and....no sound again. AGHHHHH. I cannot afford to spend another £500 on it, it is not worth it. I'm pretty good at electronics, I have test equipment, scope, signal generator etc and quite used to repairing "easy'ish" electronic circuits. I have downloaded the Korg Service Manual.
Does anybody have any advice on where I should start to track this fault down? Before it originally failed I always suspected that there may be an impending PSU issue as the chassis used to vibrate a little around the PSU area which was a little worrying.
Thank you.

[KK]

Hi there,

Lots of things can cause this. Of course, helping diagnose a problem on a forum has obvious limitations, but I'll give it a try. If I were you I would start with the obvious.

1) You mention something vibrating near the PSU. Make sure it is not an tiny object moving, especially made of metal. For example, I once found a loose screw inside my Kronos and I'm sure you know what kind of catastrophes this can cause if positioned to short something.

2) Also, start with the simple stuff. Make sure everything is tightly seated, especially all connectors going to the "hidden" PCB (the one which appear hidden under the MIDI/SPDIF one when you open the unit).

3) You mention "no line output". Do you mean only the L and R outs or also the 4 others (1 to 4) ? To make sure of this, edit a program so to route signals to those other four outputs. This test info will lead to different causes, depending if all outs or only certain ones are off.

4) As you can figure out visually, the headphones signal comes from that "hidden" PCB. On it are op-amps, NPN muting transistors, caps, etc. You will also notice a little connector identified Mute-A with two wires, grey and purple. If in step 3 you figure out that ALL outs are silenced, it could simply be that the NPN muting transistors don't receive the signal at that connector (which comes from the PSU/MOBO pair).

So if it is a global problem on that PCB with all outs off, if you feel at ease with this and everything connected as normal in the Kronos, I would monitor what happens on both these wires (first grey, then purple in another test) with reference to ground when you power the Kronos up. On at least one of them, what you measure at the beginning should suddenly change when the Kronos makes a beep after the 2 minute bootup. Otherwise, the "ready/bootup done" signal is not transmitted to the PCB.

Otherwise, if it is not a global problem on that PCB, it would be something else.