Discussion relating to all other KORG synth related products that don’t have a dedicated section. For example, OASYS PCI, M1, N Series, 01W series, T series, and more…
Hello! I recently bought a used Korg 707 FM synth and i'm trying to fix an asinine "repair" by the previous owner. Apparently what happened is that the DC power jack broke off, and instead of putting a new one, they soldered some wires directly to the motherboard, as shown here:
Since DC jacks with that particular configuration aren't available anywhere, i've decided to use a standard panel-mountable one instead:
The 707 runs both on external power and batteries, so it uses a switching DC jack with has 3 leads, where the 3rd disconnects when something is inserted. My question - is there some sort of schematic available for the 707? I can tell which lead the center pin goes to, but what about the other two? Any help is appreciated.
I'm surprised. You should be able to procure PCB mount DC sockets fairly easliy. How come you cannot find any?
Wiring should not be too complex: battery power to the switch strator, lip to go to where the power input is soldered to. Manual should be not impossible to obtain online, but I have not checked.
synthjoe wrote:I'm surprised. You should be able to procure PCB mount DC sockets fairly easliy. How come you cannot find any?
I was pretty surprised too! There are plenty of PCB-mount DC jacks available but none fit the exact footprint this one has. I managed to find the schematic for it and it says it's supposed to be a Jalco YKB31 type, but the ones on Jalco's site are not the same.
There is a 3-pin connector for the batteries and a jack labeled DJ1. Which part do you call a strator? Judging from the schematic some of the battery pins should be connected to the lead that gets disabled when something is inserted. I guess that should be easy to find using the continuity setting.
It also shows a diode running between them, would that be the thing on the left in my first picture?
Going backwards: no, the diode is not the thing on the left and the one perpendicularly above - those are L6 and L7. From the schematic I'd think that it might have been incorporated in the old connector's housing. Or perhaps it is the thing barely visible in the top left corner of the picture, but unfortunately I cannot make it out because of the quality of the picture.
As to the plug, the original in the schematic is upside down when compared to the mechanical/electrical drawing of the connector in your initial post.
What I call strator is connection No. 3 (as it does not move, a fixed contact post inside the housing). What I call 'lip' is the moving bit that the plug connects to when inserted, it is No.. 2 on the Alibaba drawing.
The pin (No. 1) is the same as the bottom contact on the schematic, connected to battery connector DJ1 pins 1 & 2. Tracing the copper conductor on the PCB from this pin should help you to find the diode, if there's one on the board. As said, it might have been part of the original connector that got removed.
The diode's function is to allow current to flow from the batteries even when the wall-wart is not connected to the wall outlet, but disallowing grid power from flowing back and (over)charge the batteries. Batteries in this configuration are effectively functioning as a backup power source, if mains is lost. In other words, you do not have to unplug the DC plug from the synth to have it powered from the batteries, when the wall-wart is out of use.
So leaving out this diode is not a huge loss of functionality, but it might be nice to have.
I see, thanks for all your help! This means that to find the strator all that is needed is to trace it to either pin 2 or 3 on the battery connector (CN7A). I'm curious now as to whether the diode is still there, or if it were part of the original DC connector. If that's the case, it shouldn't be that big of a deal to solder on a new diode there since as you said, it's a nice thing to have. The 707 is pretty low-power so i assume anything that can take 1A at 9V should be enough.
Pesho wrote:The 707 is pretty low-power so i assume anything that can take 1A at 9V should be enough.
Most likely. I was going to suggest something of the 1N4001-4004 range, but I don't know what batteries are in there and how much voltage drop is allowed, so I stopped guessing. You can try these, though - at worst the 707 will not work off batteries if the plug is in... Then you can try another diode with a lower drop.
