Reconfiguring a CMU-800 power supply from 117V to 240V?

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Reconfiguring a CMU-800 power supply from 117V to 240V?

Post by Jay200MPH » Wed Dec 19, 2012 2:23 pm

I finally got around to opening my CMU-800 up and having a look. It's a 117V (US) version... Like the title says, I want to modify the internal power supply to accept 240V input. I know you can do this really simply with some Rolands. From the schematic I have it looks like you can choose the input voltage by changing the wiring of the power board slightly, but I can't figure out exactly what to do. Here's the schematic:

Relevant part is in the far bottom left. It looks to me like I can change the input wires but I'm having trouble deciphering what the little table means.

Here's the actual power supply:

I think only processed DC reaches the board on the far left, so nothing needs to be done there... Would I have to change the big transformer (245-231C) too?

Any input is appreciated, thanks!

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Re: Reconfiguring a CMU-800 power supply from 117V to 240V?

Post by psygoat » Thu Dec 27, 2012 6:37 pm

I think the table in the bottom left hand corner is the wiring colours for for various transformers that might be fitted in the unit. The colours of the wires from the transformer match up with the column for 117volts. This tells you that the transformer is a 117v one. There is no way to reconfigure the transformer that I can see.

You will need to change the transformer.

In this case you will probably need 2 seperate transformers as there are 2 secondary taps.
One will be 230v to 15- 0 - 15v
The other will be from 230v to 0 - 5v
You don't need to alter anything else in the power supply, except for the fuse rating.
You'll need to measure the current drawn by each section of the power supply, in order to find the correct power rating for the transformer (s)
My advice is just to use an external step down transformer and not to bother messing around inside it, but if you want to, that's how you do it.

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