Hello Everyone, This will be a bit longer opening post but I want to give you all the information and history I can so you can help me solve this problem. I have a Bally Star Trek that was given to me by my Aunt and Uncle who have had it the past 21 years. I grew up playing this machine and it has always had one fatal flaw: The top saucer.

Here is the symptom: The top saucer will periodically not kick the ball out. It will not trigger during the solenoid test fire sequence at the beginning of the game or in the test mode. Then periodically it comes back. It has done this for the past 15 years at least. The same goes for the Knocker. Then one day, suddenly they will all work.

Typically we just played around it and you just "got lucky" when the game worked but now that I know a bit more about pinball electronics I want to fix it. Here is what I have done to attempt to troubleshoot so far:

1.) New MPU Board (the last one had battery damage) - Thought maybe the MPU wasn't sending the signal (not the case)
2.) New coil under the saucer- Thought that the coil was bad and not energizing correctly
3.) Checked the pins on my solenoid driver board to make sure they weren't "cold" and needed re-soldered

-After step 2 I got lucky and put about 150 games on the machine without incident. A few weeks ago my game suddenly blew the f4 fuse. I posted on the forum here and someone directed me to put a new bridge rectifier in and that seems to have solved my problems for now but I can't help but wonder if the two are related as I still don't know what caused the original F4 Fuse blow. So onto my new theory about what is going on:

I think that I need to rebuild the connectors on my transformer board and maybe my J2 and J5 on my solenoid driver board. I think that power is not being transferred to those solenoids but- then again- I am new to this and don't have great diagnostic skills yet. What do you guys think? I've attached some photos of my board pins and schematics to help jumpstart the conversation.

Thanks- Jackson

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Yes, the top saucer currently is not working. In regards to the J2 pin header, I will take a look at it but I am not having flipper issues. I will check the under playfield fuse. It is possible someone put the incorrect value in there and that is causing issues. By rebuilding the connectors I was hoping to rule out power getting to the solenoid as the issue. Since it does not fire in the test mode I know it is not a switch issue. I know that the coil is good, so the only other thing it could be is power delivery to the solenoid. (at least that is what I think) If I rebuild the connectors and still have the issues that may tell me that I have an issue with the wire run to the solenoid. I have visually inspected the bus and it all seems good. Let me know if my thinking here is misplaced.

Thanks Slochar for your advice. I do have a multimeter and will check the chain and see if either the knocker or the saucer solenoid are getting power. An update on what else I have tried: I de-soldered and resoldered all the pins of J5 and J2 on the Solenoid Driver board. I put it back in the game and no luck. But, at least I have more solid connections now.

-So are you suggesting I rebuild the J5 and J2 Solenoid connectors?

Okay. I have whipped the multimeter out and I have some more data to share. First, let me answer some questions and clear up some confusion. The outhole kicker is working. It is only the knocker and top saucer that does not work. When the ball lands in the saucer it does activate the switch for scoring. The saucer eject ball guides are there. It scores and then just sits there until removed. The solenoid never triggers. Some days the saucer will decide to magically work again for a couple of days and then break down. Currently, it is not working hence: this thread.

NEW DATA:

1) I have continuity through the coil from the left power terminal to the ground terminal

2) I have continuity from the front pop bumper power (previous coil in the chain) to the top saucer left lead power. -It does appear that this is the last coil in the chain as there is only a power and a ground to it, as opposed to the daisy chained 2 power and 1 ground.

3) I then turned the game on and put the multimeter between the under-playfield wire ground (negative lead) and both terminals on the saucer solenoid. Both sides read 44.5 Volts

4) I then took a piece of wire as Quench suggested and touched it from Q8 to the backbox ground. The solenoid DID fire.

Thank you guys so much for helping me with this. I am learning a lot and I hope that we can get to the bottom of this

-Jackson

Thank you Quench. I will run these tests this evening and report back.

Well, the saucer is now magically working again. I found out after performing these tests and putting the machine in solenoid test mode. Typically I have been running the solenoid test before I do any of our troubleshooting to see if the saucer is firing again.

I tested from TP 6 to the banded side of the Diode and the saucer solenoid fired.

I tested GRND to pin 16 and the saucer solenoid fired

Would you recommend I just replace the transistor, diode and chip at this point? I put three games on the machine now that it is working. I could always stress test it until it breaks again and then perform the diagnostic listed above again. What are everyone's thoughts on this?

Yeah Zitt, after thinking about the issues I think that is what my next step will be. I will go from the Q8 transistor and up checking and re-soldering the components just to rule out cracked joints. We can go from there if we still get a failure. Thanks for your input.

UPDATE (NEW DATA):

I Went to play a couple of games of Star Trek tonight and went to do the solenoid test to confirm that the saucer was working: it wasn't I performed the diagnostic tests that Quench has been recommending:

TP6 to banded diode: fired
GRND to PIN 16: small spurt fire then nothing

I then pulled the SDB and re-soldered all the connections pins of J4, Q8, and U3 and put the board back in.

Solenoid Test: No fire
Q8 Transistor top to Back Box Ground: Fires
TP6 to banded diode: Fired
GRND to PIN 16: Fires
Solenoid Test: Now fires

What are these tests changing that makes the saucer suddenly function? I am calling this a trend as it happened in my last post and I isolated my variables in this post by running the solenoid tests. Does this information help isolate what piece of the puzzle is not functioning?

Alright, here is what I have decided to do: I have a Marco order in for new components (U3 chip, New diode, New transistor). When I get them I am going to replace them one at a time, starting with the diode, and run the solenoid test fire and change components until things work so I can isolate what the faulty component was. Once I get the saucer working and the game playing again I will repeat the process you all have taught me to diagnose the knocker.

I will report back with my findings so those of you curious can have some closure and we can archive this post for anyone else who is having "phantom saucer" issues.

Thank you all for your help. At this point I have replaced the diode above the Q8 transistor and the game is now playing. I am going to put quite a few games on to see if it fails again. I tested the diode with my multimeter and it seemed fine until I put the leads on the area where it was soldered to the board and could not pass continuity through the diode. I think it may have had a bad connection with the SDB for those having a similar problem.