designlogik
New Member
First off just so everyone I am pretty new to electronics with regards to troubleshooting and any deep understanding of circuitry.
Okay the issue I have ran into occurred after modifying a Roland MC-303. I decided I wanted to change the LEDs to be blue. After desoldering all the original LEDs and soldering in the new blue LEDs and powering up the device I found that there is now a noticable flickering of all of the LEDs which are on. This flickering can be seen in this youtube video https://youtu.be/k7DLOdJR9u0 The flickering in the video is worse than when viewing with your eyes but still noticeable. I am not sure what is causing this flickering, my guess is that it has to do with possibly the refresh rate of a signal being sent from one of the MCUs but I am not sure. It is a DC powered circuit so we can rule out AC fluctuations. I believe the flickering may have existed before the modification but is more noticeable with the brighter LEDs. Either way seems odd to me that this is happening, and any insight regarding why this is occurring would be great.
The second issue is that after the modification some of the LEDs stay dimly lit when they should be off. I have attached a photo of this. I've looked over the schematics which I have also attached photos of and the complete service manual can be found at https://archive.org/details/RolandMc-303GrooveboxServiceNotes The LEDs are on the panelboard. I could not figure out why this is occuring after tracing the circuit and reviewing datasheets for some of the ICs specifically the TD62785, 74HC245, TD62384AP, and 74HC138 I came up with nothing. It seems like there is some stray voltage on the circuit just slightly powering some of the LEDs on, not sure why changing the LEDs would cause this to happen or how to fix this.
Anyways any help or insight on these issues is appreciated.
If anyone needs anymore information let me know, I'll do my best to provide it
View attachment 65819View attachment 65820View attachment 65821
Okay the issue I have ran into occurred after modifying a Roland MC-303. I decided I wanted to change the LEDs to be blue. After desoldering all the original LEDs and soldering in the new blue LEDs and powering up the device I found that there is now a noticable flickering of all of the LEDs which are on. This flickering can be seen in this youtube video https://youtu.be/k7DLOdJR9u0 The flickering in the video is worse than when viewing with your eyes but still noticeable. I am not sure what is causing this flickering, my guess is that it has to do with possibly the refresh rate of a signal being sent from one of the MCUs but I am not sure. It is a DC powered circuit so we can rule out AC fluctuations. I believe the flickering may have existed before the modification but is more noticeable with the brighter LEDs. Either way seems odd to me that this is happening, and any insight regarding why this is occurring would be great.
The second issue is that after the modification some of the LEDs stay dimly lit when they should be off. I have attached a photo of this. I've looked over the schematics which I have also attached photos of and the complete service manual can be found at https://archive.org/details/RolandMc-303GrooveboxServiceNotes The LEDs are on the panelboard. I could not figure out why this is occuring after tracing the circuit and reviewing datasheets for some of the ICs specifically the TD62785, 74HC245, TD62384AP, and 74HC138 I came up with nothing. It seems like there is some stray voltage on the circuit just slightly powering some of the LEDs on, not sure why changing the LEDs would cause this to happen or how to fix this.
Anyways any help or insight on these issues is appreciated.
If anyone needs anymore information let me know, I'll do my best to provide it
View attachment 65819View attachment 65820View attachment 65821