After a long hiatus (a couple months) from working on my projects due to work stuff, I am back and ready to get back into the latest and greatest the portablizing scene has to offer!
What better place to start than a 30 year old pinball machine?
This Star Trek: The Next Generation pinball machine was purchased by my dad around 2005. He told me that this machine's life started in a bar in Germany. Clearly it was imported to the states at some point, lord knows how many other owners it had, but boy oh boy, has this machine been through it! I have many fond memories of playing this game as a young whippersnapper with my dad, but as of two years ago, the machine fell into disrepair. I will do my best to tell this story through the eyes and knowledge I had as I took these pictures.
This pinball machine uses a whopping six (6) balls and, before each game, it wants to stage three of those balls underneath the playfield (one for each Vertical Up-Kicker [VUK]) for seamless gameplay. It does this by loading a ball into the auto plunger and plunging the ball, sending it to the top of the playfield. There is a hole at the top of the playfield that enters into the top of the subway system that lives below the playfield. This subway system can route balls from any of the holes in the playfield to any of the VUKs. Before each game, in order, it sends one ball to the VUK below the right cannon, one to the VUK below the left cannon, and one to the VUK on the left wire ramp.
One day, it went to stage the balls, but it just kept sending one ball to the top of the playfield and into the subway system, and then the left ramp VUK would pop the ball out and let it drain back into the ball trough at the bottom. It would do this over and over, indefinitely (and it would not let you start a game). After some quick research and learning about the ball-staging process, I learned that there are two coils within the subway system that control little diverter arms, which in-turn route the ball to whichever VUK the system wants it to go to. By default, without either of those coils engaged, the ball will go to the VUK below the left wire ramp. Having some evidence that the diverter coil to route the ball to the right cannon VUK had failed, I pulled off the glass and lifted the playfield:
Between you and me, this picture was taken significantly later, but I didn't take a pic of the playfield before I started working on it....
On the lower half of the playfield here (technically the upper half since it's upside down, but I'll stick with what makes sense staring at it), you can see the subway system and the two diverter coils attached in the center. Notice how the bottom one looks nice and new? Well it didn't used to look like that. It looked like THIS:
Toasty! Clearly the coil was no good, and the diverter arm could not move at all! Unfortunately, the machine sat in this state for almost two years while other projects took precedence, but with my break from work, I decided to get back into it. I swapped out the coil for a new one and turned the machine on and....... same behavior. It would throw a ball up to the top of the playfield and into the subway system, then spit it out the left wire ramp VUK. I didn't even hear the coil try to engage, so my next thought was a power issue. Reading through the manual, I found the circuit that supplies 50V to these coils and wouldn't you know it, there was a blown fuse. Thinking I had fixed the root cause of the blown fuse, I popped a new one in and powered the machine on. I heard the subway diverter coils fire, and the machine seemed to successfully stage three balls. I wanted to go into the switch test menu to check where all of the balls were to make sure, when magic smoke started coming from the playfield! I quickly turned the machine off, unplugged it from the wall, and lifted the playfield. Wouldn't you know it...
What happened? The coil locked on and stayed on (they're only designed to stay on for a couple seconds at a time), causing it to overheat and fry, which caused it to pull too much current and pop that fuse again. So what controls the coil? Well, most of the coils and lamps are driven by transistors on the main power / driver board up in the head unit, but Williams put too many darn coils and lamps in it! For the five games they did this in, the designed the "Aux8" board - basically just a copy-paste of the driver transistor footprint on the main driver board, eight whole times!
Main power / driver board:
Aux8 board:
In this machine, the Aux8 board controls the two subway diverter coils, as well as the two drop-target coils. Pulling this board out, I found that the transistor that controls the subway coil that had blown was shorted, meaning that it would lock that coil on when the coil was provided power (the transistors switch ground). Even worse, it looked like that transistor (top right of the set) had already been replaced at some point, meaning this has been an issue in the past. The bottom right transistor of the set (which controls the drop-target-down coil) had also been replaced... more on that later.
I replaced the bad transistor, along with its associated pre-driver transistor for safe measure. Doing lots of forum digging on Pinside, I found that this was a very common issue on these STTNG pins, and there were multiple fault points within this circuit:
That ribbon cable at the bottom of the Aux8 board goes to the MPU board, which drives it. These output signals are left floating on the Aux8 board, which could potentially lead to an erroneous latch, causing a feedback loop that would keep the coil locked on and... well you know what happens when those coils lock on now... This issue is mitigated by bodging an array of pulldown resistors (and one pullup resistor) to the bottom of the board like so:
Off camera, I also added some fresh solder to / reflowed every joint, because why not!
A second potential cause of the original failure was a design flaw of the machine. See, the four coils need to be fed 50V, which also needs to be fed as a bias voltage to the Aux8 board. Now, since the power board and Aux8 board live right next to each other up in the head, there should be a wire going right between the two, right? Right????? WRONG! Williams, in their infinite wisdom, decided that the 50V line should go from the power board up in the head, alllllllll the way down into the body, daisy-chain off of those four coils and, on the last coil, run a wimpy 22awg wire (dubbed the tie-back wire) allllllllll the way back up into the head to connect to the Aux8 board. That tiny, skimpy, pathetic little 22awg wire is known to just break off, leaving the Aux8 without the 50V bias, causing all kinds of mayhem and smoke. Unfortunately I don't have a picture, but the coil that wire was originally soldered to (drop-target-down) had been completely removed at some point, and all of the wires going to it (other than the switched ground) were stuck onto the drop-target-up coil. This would be all fine and dandy if they were soldered properly, but these wires were held on with the coldest of solder joints, to the point where I could separate the strands of the wires on the lug of the coil.....
To mitigate this whole tie-back wire issue, I made up a wire to go right from the power board to the Aux8 board inside the head unit, completely separate from the daisy chain feeding the coils. For my own sanity, I also brought each point of the daisy chain down to a single wire, that way I wouldn't have to solder two stiff wires to one lug every time I had to change a coil out (which is even more awkward when you have to dive into this machine at an awkward angle):
With a new subway coil, a new driver transistor on the Aux8 board (as well as the pullup/pulldown mods), a new tie-back wire and a new fuse, I put the playfield down, put all six balls in the trough, and gave the machine power.
Ball one gets sent up to the top of the subway, one diverter coil fires and I hear the ball roll under the right cannon VUK.
Ball two gets sent up to the top of the subway, the other diverter coil fires and I hear the ball roll under the left cannon VUK.
Ball three gets sent up to the top of the subway, no diverter coils fire and I hear the ball roll under the left wire ramp VUK.
No magic smoke too!!! I was able to start a game and play! While I don't have any pictures or video of that exact moment, here's a quick video from the future of what the machine looks like in action:
youtube.com
Now that it's up and running, it's time for some mods and upgrades, but that will have to be in another post
Stay tuned!
What better place to start than a 30 year old pinball machine?
This Star Trek: The Next Generation pinball machine was purchased by my dad around 2005. He told me that this machine's life started in a bar in Germany. Clearly it was imported to the states at some point, lord knows how many other owners it had, but boy oh boy, has this machine been through it! I have many fond memories of playing this game as a young whippersnapper with my dad, but as of two years ago, the machine fell into disrepair. I will do my best to tell this story through the eyes and knowledge I had as I took these pictures.
This pinball machine uses a whopping six (6) balls and, before each game, it wants to stage three of those balls underneath the playfield (one for each Vertical Up-Kicker [VUK]) for seamless gameplay. It does this by loading a ball into the auto plunger and plunging the ball, sending it to the top of the playfield. There is a hole at the top of the playfield that enters into the top of the subway system that lives below the playfield. This subway system can route balls from any of the holes in the playfield to any of the VUKs. Before each game, in order, it sends one ball to the VUK below the right cannon, one to the VUK below the left cannon, and one to the VUK on the left wire ramp.
One day, it went to stage the balls, but it just kept sending one ball to the top of the playfield and into the subway system, and then the left ramp VUK would pop the ball out and let it drain back into the ball trough at the bottom. It would do this over and over, indefinitely (and it would not let you start a game). After some quick research and learning about the ball-staging process, I learned that there are two coils within the subway system that control little diverter arms, which in-turn route the ball to whichever VUK the system wants it to go to. By default, without either of those coils engaged, the ball will go to the VUK below the left wire ramp. Having some evidence that the diverter coil to route the ball to the right cannon VUK had failed, I pulled off the glass and lifted the playfield:
Between you and me, this picture was taken significantly later, but I didn't take a pic of the playfield before I started working on it....
On the lower half of the playfield here (technically the upper half since it's upside down, but I'll stick with what makes sense staring at it), you can see the subway system and the two diverter coils attached in the center. Notice how the bottom one looks nice and new? Well it didn't used to look like that. It looked like THIS:
Toasty! Clearly the coil was no good, and the diverter arm could not move at all! Unfortunately, the machine sat in this state for almost two years while other projects took precedence, but with my break from work, I decided to get back into it. I swapped out the coil for a new one and turned the machine on and....... same behavior. It would throw a ball up to the top of the playfield and into the subway system, then spit it out the left wire ramp VUK. I didn't even hear the coil try to engage, so my next thought was a power issue. Reading through the manual, I found the circuit that supplies 50V to these coils and wouldn't you know it, there was a blown fuse. Thinking I had fixed the root cause of the blown fuse, I popped a new one in and powered the machine on. I heard the subway diverter coils fire, and the machine seemed to successfully stage three balls. I wanted to go into the switch test menu to check where all of the balls were to make sure, when magic smoke started coming from the playfield! I quickly turned the machine off, unplugged it from the wall, and lifted the playfield. Wouldn't you know it...
What happened? The coil locked on and stayed on (they're only designed to stay on for a couple seconds at a time), causing it to overheat and fry, which caused it to pull too much current and pop that fuse again. So what controls the coil? Well, most of the coils and lamps are driven by transistors on the main power / driver board up in the head unit, but Williams put too many darn coils and lamps in it! For the five games they did this in, the designed the "Aux8" board - basically just a copy-paste of the driver transistor footprint on the main driver board, eight whole times!
Main power / driver board:
Aux8 board:
In this machine, the Aux8 board controls the two subway diverter coils, as well as the two drop-target coils. Pulling this board out, I found that the transistor that controls the subway coil that had blown was shorted, meaning that it would lock that coil on when the coil was provided power (the transistors switch ground). Even worse, it looked like that transistor (top right of the set) had already been replaced at some point, meaning this has been an issue in the past. The bottom right transistor of the set (which controls the drop-target-down coil) had also been replaced... more on that later.
I replaced the bad transistor, along with its associated pre-driver transistor for safe measure. Doing lots of forum digging on Pinside, I found that this was a very common issue on these STTNG pins, and there were multiple fault points within this circuit:
That ribbon cable at the bottom of the Aux8 board goes to the MPU board, which drives it. These output signals are left floating on the Aux8 board, which could potentially lead to an erroneous latch, causing a feedback loop that would keep the coil locked on and... well you know what happens when those coils lock on now... This issue is mitigated by bodging an array of pulldown resistors (and one pullup resistor) to the bottom of the board like so:
Off camera, I also added some fresh solder to / reflowed every joint, because why not!
A second potential cause of the original failure was a design flaw of the machine. See, the four coils need to be fed 50V, which also needs to be fed as a bias voltage to the Aux8 board. Now, since the power board and Aux8 board live right next to each other up in the head, there should be a wire going right between the two, right? Right????? WRONG! Williams, in their infinite wisdom, decided that the 50V line should go from the power board up in the head, alllllllll the way down into the body, daisy-chain off of those four coils and, on the last coil, run a wimpy 22awg wire (dubbed the tie-back wire) allllllllll the way back up into the head to connect to the Aux8 board. That tiny, skimpy, pathetic little 22awg wire is known to just break off, leaving the Aux8 without the 50V bias, causing all kinds of mayhem and smoke. Unfortunately I don't have a picture, but the coil that wire was originally soldered to (drop-target-down) had been completely removed at some point, and all of the wires going to it (other than the switched ground) were stuck onto the drop-target-up coil. This would be all fine and dandy if they were soldered properly, but these wires were held on with the coldest of solder joints, to the point where I could separate the strands of the wires on the lug of the coil.....
To mitigate this whole tie-back wire issue, I made up a wire to go right from the power board to the Aux8 board inside the head unit, completely separate from the daisy chain feeding the coils. For my own sanity, I also brought each point of the daisy chain down to a single wire, that way I wouldn't have to solder two stiff wires to one lug every time I had to change a coil out (which is even more awkward when you have to dive into this machine at an awkward angle):
With a new subway coil, a new driver transistor on the Aux8 board (as well as the pullup/pulldown mods), a new tie-back wire and a new fuse, I put the playfield down, put all six balls in the trough, and gave the machine power.
Ball one gets sent up to the top of the subway, one diverter coil fires and I hear the ball roll under the right cannon VUK.
Ball two gets sent up to the top of the subway, the other diverter coil fires and I hear the ball roll under the left cannon VUK.
Ball three gets sent up to the top of the subway, no diverter coils fire and I hear the ball roll under the left wire ramp VUK.
No magic smoke too!!! I was able to start a game and play! While I don't have any pictures or video of that exact moment, here's a quick video from the future of what the machine looks like in action:
- YouTube
Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.
youtube.com
Now that it's up and running, it's time for some mods and upgrades, but that will have to be in another post
Stay tuned!
