My friend bought a KingKorg used from Long and McQuade out here in Canada for a song. He got it in working condition, but with none of the promised manuals or cables or anything. Just the synth, and a psu.
Well, after a while, the synth started going nuts; sometimes it would be perfectly fine for long periods. Next thing you know, the sound would get extremely distorted and quiet and basically the thing was unusable. After lengthy attempts to get any kind of help from Korg, he gave up. They were rude and did not take the time to actually answer his questions (or probably even read them). They gave him generic, nonspecific answers to simple questions which always culminated in "your warranty is expired, but take it to a Korg repair centre and have them repair it. No troubleshooting or anything.
Rather than spend a million dollars on what was hopefully a quick fix, and since his warranty was expired anyways, he sent the KingKorg to me. Well, I had to convince him to not give up on it first. Then he sent it to me.
Now, I was never able to properly diagnose the problem. There were two possibilities. Firstly, the psu given by Long and McQuade was completely incorrect. It was 15V and 400mA, when the Korg wants something closer to 12V and 840 mA. I figured this was the problem, but upon opening up the synth and removing the brain/output board from its mounts (more on that in a minute) it fixed itself. By this time I was using the proper power supply, but all I can imagine the second possibility to be is that there was a loose connector somewhere on this board. So I reseated them all and never had a problem since. Whether it was the proper psu or the connector reseats that fixed it, I do not know, but as you will see in the picture, there is a TON of empty space inside the KingKorg! In fact, the output panel has huge swaths of open area ripe for adding jacks (such as 1/4" CV outputs, or a power jack as I did), the panel boards are mounted such that they have empty mount points for screws and standoffs (allowing auxiliary boards to get mounted at will), and also quite cool: The keyboard is held in only by 5 screws and a ribbon cable (though not entirely accurate, as the bottom of the case is 99% of the structure for the whole synth including 8 more screws to mount the keyboard which you have to remove to gain access inside. Without the bazillion screws down there the whole thing is flimsy as h**l. I liken it to a unibody car). This space gave me the idea to say "screw the wall wart, let's put a power supply in this sucker".
On a quick side note, I find the easily removed keyboard an interesting prospect - maybe it's possible to easily upgrade the sucker. If not, designing and building a new case to accommodate a better keyboard and the hardware would NOT be hard due to the modularity described in the pictures below.
Well, I asked my friend and he agreed to let me take the plunge and attempt to add an internal psu so that the dreaded wall wart could be abandoned.
First, I ordered the parts from digikey: https://www.digikey.ca/short/jrb24j
[OBS] THIS IS NOW AN OBSOLETE SECTION AS THE ORIGINAL PSU IS LISTED AS NONSTOCK ON DIGIKEY. KEPT HERE FOR HISTORICAL REFERENCE.
Old digikey cart: http://www.digikey.ca/short/3zvrzr
Some interesting things to note:
The psu looks sketchy but I could find no faults with it other than the input and output not being labelled for polarity. A glance at the datasheet or a multimeter solves that problem quickly though. It has minimal ripple and it maintains its voltage and current well under load, I was very impressed. Long term we'll see how it holds up, but so far I find it a great, compact psu (which also comes in a 2A variant). I even had one or two shorts across the mains side with no problems (besides my poor breaker panel blowing).
The CONN housing is correct for the supply output, but it DOES NOT come with pins! So I ended up just soldering to the generous pads on the bottom of the board instead of finding pins and using the housing.
[/OBS]
The cables are made by digikey and are top notch, professionally made. Nothing to complain about there.
Other things I used that I did not need to buy from there are 6-32 screws and nuts for mounting, lead wire for DC, as well as a thin, yet strong material for making an adaptor plate so that the psu could mount across the mount points inside the Korg. I cut and drilled a thin plastic sheet meant to go in front of a picture frame. It worked exceedingly well.
With that all aside, mounting was straightforward. After assembling the iec connector and wires (with the ground sheath connected to ground on the connector) I mapped and routed a hole at the far side of the output panel. I then ran the wires through and popped in the iec connector. Next, I soldered all of the wires to the board (there was a connector for the mains side but I opted to remove it as the female part was not available from digikey until October. Very annoying). Then, mounted the board to the adaptor plate using screws, spacers and nuts. I noted that my spacers weren't quite tall enough to keep the nuts from shorting the panel board below (for the space between the adaptor plate and the panel) so I stuck electrical tape on each nut to keep it isolated. Then I removed the keyboard and stuck the adaptor plate with the power supply on the premade mount points I had measured for with spacers and screws. I wanted to mount it the other way, but I screwed up my measurement for the mains cables and thus it had to be flipped so mains was coming in on the middle and DC came out towards the case edge. There was ample room to run the wires neatly in the belly of the case. I then stuck a diode on the positive cable in case somebody decided to plug another 14V adaptor in while the mains was also plugged in. I considered adding a diode to the DC input as well, but I wasn't so concerned with protecting wall warts, especially since it is an unlikely scenario to prepare for and very annoying to do (it would involve snipping one of the jack's posts, and soldering a diode across the gap. It would suck). Then it was just a matter of soldering the DC leads to the jack's points and I was done. And it works like a charm! Super easy and accommodating. I very much enjoyed working on this synth. Maybe I'll revisit adding those jacks another time, if my friend wants them.
Everything is surface mount and TINY! I was in shock when I opened it up.
This is the entire SYNTH part of the synth including two effects chips on the left. It is a small auxiliary board on top of the output board and is unbelievably small, considering that a synth used to be defined in size by how much space its internal parts took up, not what size the keyboard was going to be. All of the other boards are panel boards for handling the screen, buttons, and knobs or for input devices.
I took this picture when I was trying to find out what the op amps on the output were. I *thought* they were the problem. Thank god they weren't. I can't imagine replacing surface mount madness.
A general overview of what I did. Note all of the open holes at the edges of the panel boards. Korg implemented "screw rails" which ran the length of the board mounts. I had never seen this before (I am still pretty new at all of this) but found it extremely handy.
The case was modular in design. There was the "bowl", the bottom of the case which kept everything together, but then the gold section with all of the panel controls was separable from the output panel, which included the synth itself (but on a satellite board so technically that was removable too), the cheek with the bender was also a completely separate piece, and so was the keyboard. They were held together with minimal screws making service a charm. I would assume if anything got sent back to Korg they'd take the bottom off, throw out the defective module, and stick in a brand new one, like a piece of cake. Even the tube was in its own modular section.
Here are some pictures of the final product.
Sorry the post was so long. If you have any questions or comments I'd be happy to see what you have to say! It's great to be back on the forum
EDIT: revised the current input for the synth, as it does, in fact, look for 10W not 12W power, and the stock psu from L&M was a 15V 400 mA supply, not 14V 600 mA.
EDIT 2: Updated image links so that they were not broken anymore. Also updated digikey cart since old PSU is now a non-stock part. This post will be updated in the near future as I am doing an install with a new PSU in replacement of the old one.
