I received a Korg Krome for repair of a broken power input jack. That's been fixed, but I find that the power button doesn't engage and the unit won't power on.
With an amplifier connected to the output of the Krome, a hear a 120Hz buzz when the power supply DC connector is plugged in.
Do I have a broken switch, too? Or is it supposed to be momentary, meaning, the Krome has other power problems besides the broken jack?
With an amplifier connected to the output of the Krome, a hear a 120Hz buzz when the power supply DC connector is plugged in.
Do I have a broken switch, too? Or is it supposed to be momentary, meaning, the Krome has other power problems besides the broken jack?
Look inside, is the switch in series with the power input? You should be able to see mechanically whether it is a latching switch or not.
Yes Korg did use momentaries to trigger the CPU to turn on the unit in some models.
Looking at photos, I see the square power button cap next to the power jack, which leads me to conclude it is a latching switch. I would have expected a momentary on/off on the control panel if there was one.
Make sure the power adaptor is proper polarity. using your adaptor or his?
The power supplies can be complex in there, but you can look at the ICs and find the +/-15v rails to see if they are healthy. I bet there are regulators for +5 and I'd assume +3.3v. So you ought to be able to check out the power supply at least partially.
Your web site looks pretty good. Sorry if my advice looks too basic.
Yes Korg did use momentaries to trigger the CPU to turn on the unit in some models.
Looking at photos, I see the square power button cap next to the power jack, which leads me to conclude it is a latching switch. I would have expected a momentary on/off on the control panel if there was one.
Make sure the power adaptor is proper polarity. using your adaptor or his?
The power supplies can be complex in there, but you can look at the ICs and find the +/-15v rails to see if they are healthy. I bet there are regulators for +5 and I'd assume +3.3v. So you ought to be able to check out the power supply at least partially.
Your web site looks pretty good. Sorry if my advice looks too basic.
I'm trying to decide whether to order a replacement switch before I invest an hour to take the whole keyboard apart a second time.
Using the K320 adapter. Are all K320 Korg power adapters the same polarity?
Guess I'm going to have to bite the bullet and set aside space and an hour to tear it all apart once more. Customer is not going to like the labor charge!
Using the K320 adapter. Are all K320 Korg power adapters the same polarity?
Guess I'm going to have to bite the bullet and set aside space and an hour to tear it all apart once more. Customer is not going to like the labor charge!
Korg makes many adaptors, but they would not give two different ones the same model number. In my decades on a service bench, I cannot count the times the problem with a customer unit was them using the wrong adaptor.
The symbol on the rear next to the power jack shows polarity, which is easy to confirm with a meter.
I used to have special shelves for keyboards back when I did a lot of them, they take up so much space. But if the bottom had 25 screws, and I needed to order something, I put all but two or three screws in a pill vial or film canister, tossed it inside the unit, and put the bottom back on with just the few screws I saved. Then up on the shelf. I try to avoid full disassembly and reassembly other than at start and finish of repair.
If that space is full, I put a carpet square or shop towel down, and stand them on end leaning on the wall.
It has to come apart to install a new switch anyway, so use my method to get at it now, and then the two screws will keep it together until the part comes, so no extra disassembly cycle.
The first time you take apart a particular model keyboard it can be confusing which screws have to come out and which don't.. Can I leave the key bed screwed to the bottom plate or not, that sort of thing.
You know it is entirely possible you might already have a suitable switch if you maintain much selection.
The symbol on the rear next to the power jack shows polarity, which is easy to confirm with a meter.
I used to have special shelves for keyboards back when I did a lot of them, they take up so much space. But if the bottom had 25 screws, and I needed to order something, I put all but two or three screws in a pill vial or film canister, tossed it inside the unit, and put the bottom back on with just the few screws I saved. Then up on the shelf. I try to avoid full disassembly and reassembly other than at start and finish of repair.
If that space is full, I put a carpet square or shop towel down, and stand them on end leaning on the wall.
It has to come apart to install a new switch anyway, so use my method to get at it now, and then the two screws will keep it together until the part comes, so no extra disassembly cycle.
The first time you take apart a particular model keyboard it can be confusing which screws have to come out and which don't.. Can I leave the key bed screwed to the bottom plate or not, that sort of thing.
You know it is entirely possible you might already have a suitable switch if you maintain much selection.
Regarding the power adapters, I have two different KA320 adapters from two different Korg keyboards. Both the same center positive, both 12VDC, but one is rated 2.5A and the other 3.5A. The latter unit is wider. So I'm using a power supply from a Korg PA500, which is bigger, to power the Krome because the customer had previously cut off the plug and hard soldered it to the PCB where the jack had broken off. I replaced the jack, confident that this was the only problem (repair ticket said replace broken jack) and find that the power button doesn't latch. 
I have a shop full of amplifiers in various states of undress, and I used ziplock bags for the hardware, taped to the covers. But I'm out of room. I've only got about 140 sq ft of space to work in. Just want to know for sure if that switch is supposed to click and latch, or be momentary. In which case, I need to call the customer and inform them it's going to be a lot more expensive to fix.
I have a shop full of amplifiers in various states of undress, and I used ziplock bags for the hardware, taped to the covers. But I'm out of room. I've only got about 140 sq ft of space to work in. Just want to know for sure if that switch is supposed to click and latch, or be momentary. In which case, I need to call the customer and inform them it's going to be a lot more expensive to fix.
I disassembled (again) the Krome. From what I can tell, the power switch is a MOMENTARY type. I don't see any mechanism to make it latch, so the mechanicals of the switch are not broken.
So now the question I'm pondering is "did this keyboard work at all, with the soldered on power lead that the owner had hacked together before I replaced the broken power receptacle?"
I'm going to need to find a schematic for that power input board. There's not much on it but a bunch of jacks and two capacitors and an inductor or two. That makes me suspect the problem could be on another board entirely.
Anyone know where schematics for this can be had?
So now the question I'm pondering is "did this keyboard work at all, with the soldered on power lead that the owner had hacked together before I replaced the broken power receptacle?"
I'm going to need to find a schematic for that power input board. There's not much on it but a bunch of jacks and two capacitors and an inductor or two. That makes me suspect the problem could be on another board entirely.
Anyone know where schematics for this can be had?
There is a KA320 and a KA320A, any chance that is the difference?
The key here is to look at the traces under the switch. They are either in series with the incoming power or not.
I am retired and no longer a Korg service center, or I would get it for you. You can call them in New York, but I don't know if they would release them to you or not.
Do any of these look like your switch?
Korg Switches | Parts Is Parts - Guitar Parts, Amplifier Parts, Korg Keyboard Parts
The key here is to look at the traces under the switch. They are either in series with the incoming power or not.
I am retired and no longer a Korg service center, or I would get it for you. You can call them in New York, but I don't know if they would release them to you or not.
Do any of these look like your switch?
Korg Switches | Parts Is Parts - Guitar Parts, Amplifier Parts, Korg Keyboard Parts
They're both marked KA320. No "A" suffix. One's 50% wider than the other and rated for 3.5A while the other is 2.5A. Both 12V, center positive.
None of the switches in the catalog look like this. This one's relatively square, all metal and has an embossed arrow or triangle on the top.
I've got 12VDC across one of the caps on that PCB and 5VDC across the other cap when the power supply is plugged in and energized.
I've checked all the ribbon cables, thinking that maybe I'd left one disconnected, but they're all inserted and no bent pins.
What I'm concerned about is that there might be some fault on the microprocessor board that's preventing starting. I think this uses a circuit similar to a PC as far as controlling the startup of power supplies. It could be possible that the customer sent it in for repair because it stopped working, not because he'd soldered the wire from the power supply to the place where the broken off connector was on the PCB.
To troubleshoot this further, I'm going to need to know what signals are supposed to be present when starting up. Where housekeeping power is to be found and what the startup sequence for the power system on board is.
None of the switches in the catalog look like this. This one's relatively square, all metal and has an embossed arrow or triangle on the top.
I've got 12VDC across one of the caps on that PCB and 5VDC across the other cap when the power supply is plugged in and energized.
I've checked all the ribbon cables, thinking that maybe I'd left one disconnected, but they're all inserted and no bent pins.
What I'm concerned about is that there might be some fault on the microprocessor board that's preventing starting. I think this uses a circuit similar to a PC as far as controlling the startup of power supplies. It could be possible that the customer sent it in for repair because it stopped working, not because he'd soldered the wire from the power supply to the place where the broken off connector was on the PCB.
To troubleshoot this further, I'm going to need to know what signals are supposed to be present when starting up. Where housekeeping power is to be found and what the startup sequence for the power system on board is.
OK, then they just upgraded the adaptor model. Sorry.
I have been looking for your schematic, we'll see if it pays off.
Here is a thought: I see two Korg dealers in Danbury area. Bethel Music Center in Bethel. And GUitar Center #524 in Danbury. IS that about ten miles? You might drop into one of those stores and check out a Krome to for sure answer the function of the switch. Korg lists both stores as Krome dealers.
If the switch is momentary, then you are right, the switch triggers the CPU to wake up from sleep mode.
I have been looking for your schematic, we'll see if it pays off.
Here is a thought: I see two Korg dealers in Danbury area. Bethel Music Center in Bethel. And GUitar Center #524 in Danbury. IS that about ten miles? You might drop into one of those stores and check out a Krome to for sure answer the function of the switch. Korg lists both stores as Krome dealers.
If the switch is momentary, then you are right, the switch triggers the CPU to wake up from sleep mode.
I pulled the Krome apart again as described in post #9 and closely inspected the power switch. It IS a momentary, which differs completely from the PA500, which I also repaired this week.
I do have 12V and 5V (measured at two capacitors) on that input PCB. So it's starting to look like there may be a more serious problem on another board, but without a schematic, there's not much I can do.
I do have 12V and 5V (measured at two capacitors) on that input PCB. So it's starting to look like there may be a more serious problem on another board, but without a schematic, there's not much I can do.
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