Jokerz issues

[Kraken]

Well I sold Jokerz to my buddy a couple weeks ago, and now he's having issues with it. Normally, when a ball goes into the hole on the upper left of the playfield, it awards some boints, then a coil pops it into the BET area. For some reason, the coil stopped working, and the ball just sits there while the knocker coil fires repeatedly (about once a second). If you remove the ball from the hole area manually, the knocker stops firing. Usually, the knocker has nothing to do with the BET hole. The diagnostics point to one of the bottom left 3-bank drop targets (bottom), and all three of the top left 3-bank targets. Checking the switch-matrix table, it lists GRN-YEL in the column for the bottom left and GRN-BLU in the column for the top left. I'm new to repairing still, but I assumed that table tells you what color the wires are for each particular item. Is that correct? I traced the green and yellow wire and the green and blue wires all the way to the board, and didn't find any shorts. After checking all the fuses and making sure all the connections where good, I turned the machine on to see if the problem persisted. It did, and while I was contemplating my next move, the knocker started smoking really bad. I shut it off as quick as I could and unplugged the knocker coil. The same errors come up with the knocker unplugged. What would make the hole switch trigger the knocker? And why did the knocker coil burn up all of a sudden? I don't have any toasted fuses, and they're all the correct amperage. Anybody have any advice on what I should do next? I really don't know where to go from here.

[eric]

Knockers are used in a lot of System 11 games to alert operators to problems.

Go into switch test (switch edges is what it's called in the diagnostics menu) and throw the ball in the top left kickout. Does switch #44 (TL Kicker) register. If not test, other switches in its row (4) and column (6). If all appears good, go into solenoid test and see if solenoid 5A (the TL kickout) fires.

[Kraken]

I'll give it a shot tonight. As always, thanks for help Eric.

[Kraken]

The switch does register on the test, but the coil won't fire. It doesn't fire during the diagnostic test either. It doesn't look like it's cooked or anything. Testing across the leads with my DMM, it reads 4.6 ohms. There's another coil with the same part number on the playfield, and it registers the exact same. Is it still possible that the coil is bad? It seems more likely that there's a short somewhere else, especially since the knocker coil burned up. Of course, I really have no idea what I'm talking about either.

[Opto]

Bad diode on that coil and/or corresponding transistor on the driver board - Eric?

[eric]

Yeah, definitely sounds like a bad transistor on the driver board. You bought that soldering iron, right?

[revtest]

That's what I was was thinking. do you have the manual/schematics??? I'll call you tonight or txt me when you guys are home from work. tonight or wed night are good for me.

Jake

[Kraken]

Yes, I have the new iron, and I do have the manual w/ schematics. How do I test the transistor? Is it as simple as checking continuity, or am I looking for specific voltages, or values for certain transistors?

[eric]

There are 3 legs on the transistor - the base, the collector, and the emitter. A simplified explanation of what's happening is the MPU pulses 5V to the base of the transistor. When this voltage is applied it allows current to flow from the collector (playfield coil) to the emitter (ground).

To test this particular transistor, make sure the power is turned OFF on the game and set your meter to diode test. Put the black lead on metal tab sticking out the top of the transistor (the collector) and put the red lead on either one of the outside legs. You should see something between .4-.7V. Now move the red lead to the other outside leg. Again, you should see .4-7V. Test both the top left kickout transistor and the knocker transistor as both are suspect.

Also, if the knocker coil was smoking you should definitely test its resistance with your meter before reconnecting it.