Yesterday in the middle of a game a ball went down behind the trunk and into the ball-lock, then nothing happened. The coil for lifting the trap door fired a few times (no ball popped out) and then it soon went into ball search. Took off glass and removed the ball from the subway.
Put all balls into the trough, started a game and put the 1st ball from the shooter lane manually down below the trunk. Game apparently "locked" the ball successfully as it didn't come out from trapdoor and instead ejected ball 2 to the shooter lane. Took ball nr2 and also put it down below the trunk and this time nothing more happened. No 3rd ball ejected into shooter lane. I think game went into ball search after that, not entirely sure.
Opened coin door and tried to enter the service menu but no buttons seemed to work, at least no text changed on the DMD which I found weird.
Turned of game again and checked all fuses; found both F903 and F904 on the Fliptronic board were blown. The manual states F903 & F904 are for the lower right and lower left flippers but as far as I can remember both flippers was working when all this happened which is strange. According to the manual F901 and F902 are for upper right/left flippers (which this game obviously doesn't have as its a two flipper game). I think I've read somewhere that on games with only two flippers the fliptronic board controls other coils too (probably the physical ball lock coils on this game).
I've checked every coil connection in the game and all were soldered firm, no loose ends. I haven't done any maintenance on this game for at least a month so no recent tinkering with it that could be the cause. Also did an extra visual check around the physical ball lock regarding switches, loose stuff or anything touching metal parts and so on but nothing strange found.
I guess I could just turn it on and see what happens but as both fuses had blown pretty hard (black speck on the inside of fuse) I'm worried that replacing them and turning the game on would blow them again or even worse damage other components (if that haven't already happened).
If the blown fuses directly corresponded to the ball-lock coils I wouldn't hesitate as much but now I'm confused as F903/904 indicates problem with the flippers (according to the manual) but if I recall correctly they both worked before turning off the game and it seems the fault is at the ball lock where I don't see any problems at all.
Any advice on what to check or should I just bite the bullet and test turning it on and see what happens?