wpc powerup issues

[lilshawn]

Gilligans island pinball, WPC.

had a report of the balls not kicking out. checked and found a blown fuse on the power board and a melted right sling coil.

replaced the pre-driver transistor and main driver transistor as well as the diode on the board for the sling to be sure...

take the board back to the machine and replace the melted coil.

Power up the machine and it sounds like 3 solenoids lock on. the knocker for sure and something in the top left of the play field (maybe left lock). not sure what else. kill power.

run around and check all my plugs to make sure they are all plugged in and in the right place. missed a plug...its for the flashers. not a big deal.

power up again, knocker locks on, seems to be the only one. see left sling twitch out of the corner of my eye just as I  kill the power again.

pull the plug for the knocker solenoid and power up the machine again. after about 3 seconds i see a tiny little flash on the diode for knocker.

sigh.

[lilshawn]

so i replaced a handfull of transistors. (not a big deal) i pulled out the 74HC374 chip (big deal) and tested it. tested okay. let's not talk about removing it and what a mess it was to fix the board.  least it's in a socket now so if it does crap out it will be easy.

so lesson 1: IC chips- cut the ---goshdarn--- legs off the package and just buy a new one. don't bother trying to salvage it.

anyways I take it down there and power it up... arc again. 

this time i'm watching out for it and definitivley find it's source. it's coming from d26 (the diode for the left sling) it's arcing to r108... some kind of biasing resistor for the input on the predrive for the knocker. (not the diode FOR the knocker as previously stated)

now it's making sense. sling twitching knocker locked on.

when i first encountered the board i replaced the diodes. this particular diode is VERY close to R108. like REALLY REALLY close. the solder pads almost touch. when i soldered it i must have used slightly more solder than what was originally there. not a bridge, originally not close enough to arc but with the addition of a tiny bit it was close enough to arc.

long story short blew the transistor and locked on the left sling solenoid. knocker wasn't operating. have a feeling the predrive transistor was blown by the initial arc... replaced predrive/drive transistors for left sling and predrive for knocker. I may just go ahead and replace the 74HC374 to be sure... high voltage it's real great for them. Trimmed back the solder pads on both sides to create a gap between them.


so, it's not exactly related to the initial right sling getting fried, but my repair caused another issue to creep up.