Thursday, October 20, 2011

Badly soldered BR3 caused weak coils

Repaired a WPC pinball machine this week. Fuse F112 on the powerdriver board always blew, because BR3 had shorted.

Replaced BR3 with a new bridge rectifier. Worked quickly in less than ideal conditions (dark environment, above the playfield, ..).
Put the powerdriverboard back into the game, played a game to test everything.
I noticed some coils were weak: the automatic ball launch could barely get the ball onto the playfield, an upkicker also could barely kick the ball high enough so it got onto a ramp, sometimes it fell back down into the kicker..
Weird ?!

What really was strange was that the behavior wasn't consistent. The ball wouldn't get launched onto the playfield (just couldn't make the ramp) and rolled back in the shooter lane.. and a second kick of the coil would kick it hard enough and then it would end up nicely at the back of the playfield. The upkicker would try one or two times and then the pinball did make it correct.

Time to check everything I changed and parts involved.
The bridge rectifier was the correct type. Checked the new fuse I had put into to make sure this was also a good type. Checked all connectors. Measured voltage at the coils, which was also high enough. (I first thought it would be too low.)
And still the coils were weak ??

Double checked the bridge rectifier I had replaced. When I had soldered it in, it was almost touching the heatsink of the transistor that's below BR3. I had pushed BR3 a bit above so there was some more distance between the parts. Pushed BR3 again, and one leg came loose ?  Oops.. Seems it wasn't soldered well enough - one of the metal legs of the bridge rectifier didn't completely go through the board but ended about level with it. Either the connection was too thin for a lot of current to pass, or maybe there was some vibration that caused it.. anyway I resoldered the leg, added a bit more solder to all legs to be sure, and the problem was solved ?!

No comments:

Post a Comment