Live to Fly Again
The Star Trip MPU-1 Rebuild Page
In the beginning was the Star Trip Pinball Machine
Looks nice from this angle. A little warping on the apron plastic, no major wear on the playfield, but…
The MPU board with the original NiCad battery, and what happens if it isn’t removed. Components and traces eaten alive.
The Damaged components and all sockets were removed with care and the board was then rinsed with White Vinegar to neutralize the leaking nicad’s chemical corrosion.
Cleaning the board with White Vinegar, Sanding, cleaning with Rubbing alcohol
Re-tinning the traces. I used the Flux commonly used to solder copper pipes. It is a mild acid that helps to prepare the surface so that solder can stick to it.
The traces after tinning (applying solder) Looks pretty good now.
Solder Wick Braid was soldered on top of the wide trace just below the PIA and PROMs. Other traces were repaired by using 30 AWG wire and soldering it to the top of traces. When there was a larger trace, multiple strands of 36 AWG wire were twisted together and soldered on the trace. I also used one 22 AWG green insulated wire to take a larger power trace across the bottom of the board. Sockets and components were re-installed using the layout from the parts list in the Star Trip Manual. You will also notice that all of the big green disk capacitors have been removed and replaced with smaller yellow ones. These big green disks were bent over multiple times and I did not trust the connections anymore, so all were replaced. Notice that the battery is not installed yet. I did buy a “memory” capacitor to replace the battery, but I will leave that off until the board is working.
The next problem will be getting the proper PROMs or EPROMs for this board. The original used PROMs since it was a high volume application. These are expensive to make if you are only making a set or two, however if you are making hundreds, they are rather cheap. Unfortunately, the EPROMs that I can buy today have a slightly different pinout than the PROMs that were originally used. This was foreseen by the designers and a “Cut and Strap” table was added to the schematics to allow for this. There are several traces that need to be cut and more jumpers that need to be added, the PCB has all of those locations ready, it’s just that they are not labeled. So now armed with the schematic and a camera, I will try and locate all of those locations
Cut and Strap for the Game Plan MPU-1 Board
After the completion of the rebuild of the MPU, it needed to be modified to allow the new EPROMS that are 2716’s installed where the old mask ROMS were installed. After looking at the pinouts of the 2716 and comparing them to the schematic, there were only 3 pins that did not match up and needed attention.
|
Pin |
Rom |
Prom |
Action |
|
18 |
OE~ |
EO~ |
2 cuts and 2 jumps |
|
20 |
A10 |
OE~ |
1 cut and 1 jump |
|
21 |
-5V |
VPP |
1 cut and 1 jump |
Working these in numeric order we start at Pin 18. There are two cuts of the PCB traces that need to be made as shown in the two pictures below:
U13 U12
The X-Acto is pointing to the location of the first Cut. This cut should isolate U12p18 from U13p18.
The second cut location is shown in the following picture:
U11 U12
This isn’t quite as good a photograph. But this cut isolates U12p18 from U11p1. The test leads are connected to a DVM that is set to the continuity setting. This setting will make a noise when there is a connection, and in this case, stops making noise when the connection is broken. Now for a better picture of both cuts:
Cut #2 Cut #1 U7 U6 U13 U12
At this point U12 and U13 should be isolated from all other connections on the board.
Now there are two jumpers that need to be added to the board to finish out the pin 18 changes, they are shown in the following picture:
Jumpers for U5p6 and U5p11 U6 U13 U12 U11 U5
These locations look like there should be a jumper installed, they are easily found. The left one is connected to U5p6 and the right one is connected to U5p11. Once these two jumpers are installed, verify the following connections:
U12p18 to U5p6
U13p18 to U5p11
No Connection from: U12p18 to U13p18 or U11p1
The pin 18 modifications are done, now we will start on the Pin 20 Mods.
The following photograph shows the location of the cut trace for the Pin 20 Mod. The trace from pin 20 has a hash mark across it to help locate the cut. Note the part and pin orientation as viewed from the back side of the board in the next picture:
Cut Here U12p20 Pin 20 U13 U12 U17
Once the cut is complete verify that there is no longer continuity from U12p20 to U11p5.
Add a jumper at the following location as shown in the photo below:
Jumper Location U13p20 U11 U12 U13
Once the jumper is installed, verify the following connections:
No Connection from: U12p20 to U11p5
Connections from: U12p20 to U13p20 to U17p5 to U11p21 to U10p6
Now that pin 20 is completed, we will move on to the last pin to modify, pin 21.
The one cut that is required is shown in the photograph below. There is a hash mark on the tract at the location of this cut as well. Cut on the side of the trace that is closest to pin 21 of U12.
Cut Location U12p21 U12 U13 U11
Once this cut is complete there should be no continuity from U12p21 to U11p19.
The jump will connect the 5 volt supply to pin 21. The best location that I found to do this was on U13. One end of the wire will be at a through hole on the PCB, the other end will be at pin 24 of U13. The following picture shows the location:
Jumper from U13p24 to U13p21 through hole U13 U12 U11
Now U12p21 and U13p21 should be connected to the 5 volt supply.
Now that this is done, it is time to see if the MPU Board works.
New PROMs were obtained from John Wart, who does a great job of reproducing old PROMs and new ones as well. His website is:
http://www.thatpinballplace.com/eproms/index.htm
Any components that showed acid damage were replaced, and this included the PIA at U17. This, and other electronic components including sockets were obtained from Jameco. When they are all installed, the board looks like this:
I have not installed the battery backup capacitor yet, that will be done once everything in the game is working.
I tested the board on the bench after the games power supply was verified. The test setup looked like this:
Using the power supply from the pinball machine I was able
to get 6 flashes out of the diagnostic LED on the MPU Board. From the game manual, that is completely
through the boot sequence.
This is picture of the inside of the Star Trip with the MPU installed. The MPU is in the center of the picture with the long gray cable leading to it.
The Game now boots and plays, but the play is a little weird. Diagnostics run fine and there are two issues, First a couple of the segments in the player 1 window are dim, and second, there are three switches that do not register in the switch test. During game play, those switches do not work, however there are three other switches that act like they are the open switches. A preliminary check of the playfield shows that the wires are there and are not shorted. Further investigation is forthcoming