Damper circuit help please

30Rocks · Post by **30Rocks** » Mon Dec 02, 2019 6:41 pm

Hi. First time on forum. Happy holidays. I have a technical question on a Korg SP-250. Damper does not work. I have changed the oem jack which was loose on the circuit board. I have checked for continuity on Korg pedal/cable/plug. I have checked using a known good pedal as well. I am skilled at circuitry, however this one has me baffled. Ideas please?

voip · Post by **voip** » Tue Dec 03, 2019 5:04 pm

Which damper pedal is it, and what are the resistance measurements between tip and sleeve, and ring and sleeve, pedal up, pedal mid, and pedal down?

Also, plug a plain TRS jack to jack cable into the Damper jack socket and measure the DC voltage between tip and sleeve, and ring and sleeve.

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30Rocks · Post by **30Rocks** » Tue Dec 03, 2019 10:09 pm

The pedal is a Korg model 530000000317. I believe it is the oem that is sold with keyboard. This is a molded mono (tip/sleeve) plug.
Per your queries: tip and sleeve (no ring, mono plug)
Resistance tip and sleeve: Pedal up: open
mid: 1.5 to 2.0 ohms
down: 0.1 ohm

Using a unterminated stereo plug (tip/ring/sleeve) plugged into the damper jack on the keyboard:
Keyboard power on. DC volts: Tip/sleeve: 0 vdc
Ring/sleeve: 0 vdc

30Rocks · Post by **30Rocks** » Tue Dec 03, 2019 10:20 pm

FYI...with the trs plugged into the jack...shows that all 3 contacts are open between each other. In other words, there is no continuity between tip/ring, tip/sleeve, ring/sleeve. The previous jack was intermittent internally, not on the circuit board, and a new oem jack replaced that one.

voip · Post by **voip** » Tue Dec 03, 2019 10:58 pm

From the info provided, it would seem that the issue is likely to be inside the SP-250, since there should normally be a potential difference of around 3.3V between tip and sleeve.

30Rocks · Post by **30Rocks** » Wed Dec 04, 2019 1:09 am

Thank you...I will trace back to find the 3v supply. Without the circuit schem I'm looking at a coil and 22k resistor on the board that appears to go to a buss...calling it quits on it for the day...will trace it back tomorrow to find and get back to you. Again, thanks.

voip · Post by **voip** » Wed Dec 04, 2019 12:21 pm

It might be worth moving this discussion over to the Korg Pianos (General) section, as this part of the forum is more intended for new members to introduce themselves.

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30Rocks · Post by **30Rocks** » Wed Dec 04, 2019 11:12 pm

Before I ask how to move the topic to the other section...
Thank you for sending me in the right direction! You supplied the info for the 3 vdc that should be at the connector. There was a hairline crack on the etched circuit board between the 1/4" damper jack tip, and the resistor in series with that jack (R 64...probably used as a "fuse" of the 3 vdc to the tip). This crack broke the 3 vdc to the tip of the damper jack. A simple jumper under the circuit board to bypass that crack and all is back to perfect! Thanks much.
(*NOTE to any amateur technicians: When making any changes (adding jumpers, upgrading circuitry, always tape a small note in the unit with your work to allow next technician to follow that circuit, as opposed to the manufacturer's schematic. That little note will save hours of troubleshooting.)

How does one post a messege to the correct zone or group?

voip · Post by **voip** » Thu Dec 05, 2019 9:16 am

Good news on the repair :-)

Regular users cannot move a thread on a topic to another part of the forum. Only the moderators can.

The simplest way, for us mere mortals, would just be to post a message to say the thread is continuing in section ...<section name> Adding a link would be helpful.

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