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Will using the RP-SM304A alter the sound of my BX-3 or CX-3 in any way?
No. The function of the RP-SM304A has nothing to do with tone generation.
How can I tell if my SM304A is bad?
We know of a web site for the diagnosis and repair of Vintage BX-3 and CX-3 organs at It should be fairly easy to tell, using their troubleshooting guides.
What if I get an RP-SM304A and it doesn’t fix my organ?
The SM304A are used in pairs. It’s possible that if you replaced one, the other may also be bad. We suggest that you visit the web site at to determine if there may be other problems. If you determine that the organ is too far gone to justify the repair, or if your original SM304A parts turn out to be OK, you may contact us with 30 days to get an RMA Number to return your purchase. See our return policy for details.
If my organ burned out the original SM304A, won’t it burn out the RP-SM304A replacement, too?
No, the original SM304A IC most likely wasn’t burned out by the organ. It seems that the was something faulty in the manufacturing process of the SM304A, and they tend to fail all on their own. We have even heard reports of organs failing following long periods of storage. The RP-SM304A is designed to have a very wide operating margin, and should last as long as the rest of the organ. We do recommend that you verify that the supply voltage is correct (see the question, How can I tell if my SM304A is bad?) before installing the new part.
I have a bad SM304A in an instrument other than a Korg BX-3 or CX-3. Will the RP-SM304A work in another instrument?
Maybe yes, maybe no. We became aware of additional functionality in the Siemens SM304A that is not exploited by the BX-3 and CX-3 after we designed the RP-SM304A. The best thing to do is to contact us for advice. Having the instrument’s schematic available for us to see will be very helpful.
My BX-3 / CX-3 has a bad SM305. Can you replace those parts, too?
Yes. We have new old stock for the original Siemens SM305A and SM305B. The part numbers are 39-00003051 for the SM305A and 39-00003052 for the SM305B.
How can I purchase the RP-SM304A at a discount?
If you want to purchase several units for your repair business or even for resale, contact us for details. Also, we may have refurbished or “cosmetically-challenged” units from time to time. They are fully functional, and carry the same warranty as new units. Contact us for details.

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