Bonus Error - Nishijin Y&O model - Splenby

[Nascarjake]

Hi everyone,
First post here, hope this is the right section, if not please let me know.

Recently started collecting machines, I have just a few right now, and so far have had great luck with them.
My most recent find is a Nishijin Y&O model, the Splenby themed machine.
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Having an issue with an error, only happens during bonus mode when the door is open.
Error Symptoms

- Alarm sounds
- Balls flow freely and if they land in a pocket it pays like normal.
- Bonus Door closes
- LCD changes to error screen
- Machine actually continues playing but no spins and subroulette

Known work-arounds
- if I open the playfield and open the door myself and stick a ball in it, the alarm stops and the bonus ends. Play resumes normally.
- Using the power switch, off and on results in a black screen most of the time. Manually opening the bonus door as above resumes play
- Unplugging and plugging back in results in a normal boot forgetting about any bonus.

Seems to happen every bonus. Don't think I've ended a bonus successfully on this machine.

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Error Codes:
- LCD error message in Japanese translates to "Error occurred, please contact associate"
- Back has a error LCD with sticker. LCD flashes code "O" during the error. Translated the sticker and it says "normal action"

**During normal play, on a fresh boot, or after using a work around to solve the error, the back LCD flashes "O"
I do see it flash other letters on boot when its checking systems, mainly, "A" which the sticker says means "Accessory board not attached"
It is a CR machine and I don't have dave's dongle yet. Not sure if that's related.
This tells me I'm not really seeing an error code when the alarm is sounding? It's just acting normal?

Ball Sensor and/or Shortage
I should also note that I've done this multiple times and at first I thought it was a ball shortage.
However I have run out of balls during bonus (and other times) and didn't get the error, and I've also gotten the error with a full blanket of balls in the tray.
Adding more balls doesn't solve the error.

Is this some sort of setting that calls an attendant after every bonus? Can I disable it?

Thanks for reading!