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Arjan
Joined: 02 Jul 2008
Posts: 39
Location: Netherlands
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 Posted: Tue Aug 05, 2008 8:31 am Post subject: How to modify a Korg CX3 for 220V AC operation? |
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Hi,
I have ordered a Korg CX 3 (the modern digital version) from Sweetwater. Even though I'm in Europe I had to order it from them because it is no longer sold anywhere in Europe.
As it turns out the CX3 appears not to have an auto-sensing
power-supply, it will only take 110/117V. I don't really want to use an
external transformer so I'm looking at modifying the internal PSU to
take 220/230V.
Bruce Wahler over at the clonewheel support group mentioned that
| Quote: | The CX-3 is NOT a "universal voltage" model. IIRC, it can be
changed to the other voltage range, but it requires a soldering iron.
Don't hold me to it ...
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So that made me think that the PSU was an actual old-fashioned
transformer and I could just tap the second winding at a different
point, but having obtained the Service Manual it apears that it is a
switching power supply after all.
By switching power supply I do not mean that it will take different
input voltages, I am merely referring to the design of the PSU.
Now does anyone here have any information on what the best/easiest
approach would be to make this unit take 220 instead of 110? I have
thought of three different ways:
- It may be possible that Korg used the rectifier stage to double the incoming voltage when used with 110V external power and that for 220V external power the rectifier stage only is modified. Some power supplies actually allow switching between these two modes of operation with an internal or external switch but if Bruce is correct this is not the case in the CX3, hence the soldering iron.
If anyone has any details on the schematics and changes required please
let me know. Unfortunately the Service Manual has only limited
schematics on the power supply board. Only the stages coming after the
actual PSU are detailed, you can clearly see the well known 78L05
regulator being used as well as a BA033T which also appears to be a
regulator used to generate 3.3 V.
If I knew what to change exactly this could be the simplest (and definitely the most cost-effective) solution by
far.
- Completely replace the PSU with something else.
I won't be able to assess this possibility until I open her up
- Include an internal 220->110 converter and reroute the AC
receptacle wires to this converter and feed back the 110V into the main
circuit.
Again I won't be able to see if there is room for such a converter until
I open the unit
- There is of course a 4th way and that is to use an external
transformer. The main reasons I don't want that is because a) if I
forgot it I won't be able to use the thing and b) if I or someone else
inadvertently plugs in a power cord straight to 220 it may fry my CX3.
If any of you (anyone from Korg listening?  ) have any information to help me that would be greatly appreciated. I'm an Electrical Engineer so don't worry about me being electrocuted, I know what I'm doing. Also I will be testing the unit with my external 220->110V converter that I already have lying arond before I start to mess with it and I should be able to test my modifications on the PSU board in isolation.
BTW expected delivery date of my CX3 is August 7, this Thursday. I actually just got a fax that is has already arrived at FedEx Netherlands and they that it is going through their their customs clearance procedure
Unfortunately I don' t have my 220->110 converter here, I'll be picking
it up over the weekend. 
Thanks,
Arjan
P.S. My Service Manual, which I ordered from Parts is Parts, turns out
to be Revision 1.00, Provisional Version. If anyone has a more complete
or uptodate service manual please let me know. |
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Arjan
Joined: 02 Jul 2008
Posts: 39
Location: Netherlands
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| Posted: Thu Aug 07, 2008 10:21 am Post subject: |
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Well, it turns out it's pretty easy to modify a US model CX3 taking 117V to a European model taking 230V.
The rectifier stage of the PSU turns out to be a simple one-diode half-wave rectifier so no voltage doubling taking place there. Lacking any knowledge on how the PSU itself may be modified to work with 230V, I decided to go the other route and install an internal 220->110 transformer inside the CX3 as there is plenty of space. The fact that the case is all wood makes this very easy, transformer and all extra wires are easily secured with some wireholders and screws driven into the wood.
Works like a charm. Now there is no risk of someone inadvertently forgetting to use an external 220->110 transformer and thereby frying my new toy.
From the outside you don't see a thing, although I did apply a sticker on top of the serial/power rating label so that it is now properly labeled ~230V. I'm a happy camper |
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dave
Senior Member
Joined: 01 Jun 2002
Posts: 402
Location: Dublin, Ireland
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| Posted: Thu Aug 07, 2008 12:04 pm Post subject: |
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Thank you for posting this information, Arjan. In the future, some poor soul faced with this problem will find your posts very helpful.
Kind regards.
_________________
Dave Bourke
- ideation - |
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