Hi everyone! For some time now—following a power outage—my Korg Krome 73 won’t turn on. Convinced it was a power issue, I replaced the power supply and then the power board, but it still won’t start up; not even a single LED lights up. I fear the mainboard needs replacing; I checked, and voltage reaches the unit when the power button is pressed, but nothing happens. I was wondering: is any kind of programming required, or is it enough to simply buy the replacement part and install it? Does firmware need to be loaded, or is it pre-installed? Are there any special steps I need to take? Thanks!
Do you have the service manual? I would start by checking the 5 power lines on page 6. Korg didn’t make it easy.
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Thanks a lot for your interest! As I mentioned, voltage is reaching the mainboard; the +12V and -12V rails are present—just as you suspected—but the other voltages are missing. I’m not sure if it’s a component issue or if the ICs themselves have failed, but IC19 is receiving voltage yet not outputting the 1.8V. Based on the schematic, I assume that 1.8V is needed by IC18 to generate the 5V, which in turn feeds IC28.
Hopefully its just a power supply problem.
Inspect the chips and check surrounding components and continuity to each other with a meter.
Ensure there are no shorts on the 1.2v, 1.8v, 3.3v, 5v rails
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First of all, thanks for the reply.
From what I’ve been able to gather, there are two nearly identical circuits connected to pins 2 and 13 of IC19; I focused mainly on the differences by probing around with my multimeter.
- First, I found an open circuit between all the power rails, except between the 1.2V and 1.8V lines, where I measure a resistance of 357 ohms, I’m not sure if this might be due to a discrete component.
- Secondly, I’m suspicious of the Schottky barrier diode D3. When testing with the diode probe (and I’m not sure if that’s the right tool for this type of diode), D2 shows a reading of 400mV and a “good” status, whereas D3 shows 200mV and “bad.” Otherwise, all inductors show continuity (closed circuit) and all capacitors show an open circuit. I haven’t found any damaged traces. I still need to finish testing all the resistors, but so far, R103, R104, R105, R106, R107, and R108 appear to be open circuits (though I’ll investigate further), while R100 and R111 correctly measure 10 ohms.
In addition to the valuable tests I’m running based on your advice, I’d like to ask for your opinion on something else:
regarding my initial question, if the mainboard can’t be repaired and I have to replace it, is any programming required, or is the new board (assuming it’s functional) ready to use right out of the box?
I’ll add one more wild idea: I haven’t found a mainboard for the Korg Krome 73 online, but I did find one for the Korg Krome EX 73… the connections seem to be identical, do you think it might work just the same? (Aside, of course, from the advantages offered by the EX version.)
Thank you for your patience.