Quoted from PinMonk:The playfield GI is powered in sections. Does just the lower GI go out? Usually if it's a short in a bulb or bulb socket, there's a second page on the tech message to tell you what section to check. But since you just have 1/1 there's no second page here.
So basically to narrow down where the short is, you need to unplug connectors from Node8 one at a time and play. You'll lose insert or GI lighting for that area, but if it solves the problem you know where to look.
So on node 8 (the rectangular board by the flippers under the playfield) unplug
Connector labeled CN15 - bottom GI red/white/blue
And then play and report back.
I unplugged the CN15 and played three games with no issues. The last one was a really long game too where I set a new high score.