Not my writings but here's some gold dust.
Heres some more info is the coil locked on when you powerup your game?
this probably why the fuse is blowing and could be from a locked on coil sm1-26-600
or the other coil in your pics the one with the green wrapper starting with AE-
or faulty transistor Q13 on the 8 driver board.
Games with Solenoid Numbers Above 28 (Auxiliary Driver Board).
Even though the WPC driver board only supports solenoids 1 to 28, there can be solenoids numbered up to 44. Most often seen are numbers 29 to 36, which use transistors in the fliptronics section of the board. If the game only has two flippers, the fliptronics section will have two flipper power (TIP36) and two flipper hold (TIP102) transistors that may be used by the game for things other than flippers. Also several games (
Indiana Jones,
Twilight Zone, Demo Man,
roadshow and
Star Trek Next Gen) used an 8-driver auxiliary driver board, which contained eight more TIP102 transistors for even more flash lamps or coils. Note this board also contains circuitry for an extra ninth switch matrix column (used on STNG, Twilight, Indy Jones only).
This auxiliary driver board could be problematic, especially on Star Trek Next Gen. On Star Trek, this board needs +50 volts for a "tieback diode" voltage for the circuit (because it controls solenoids, and not just flashlamps; all the other games that use this Auxiliary driver board only control flashlamps). The 50 volt tieback power is connected by a thin violet/yellow wire which connects to the playfield's single drop target coil (at the back of the playfield), and goes to the Auxilary Driver Board. If this wire breaks, or if some other power wire in this coil power daisy chain breaks, it can cause the two under-playfield diverter coils to lock on (after they're first activated in game play!) If the problem is not found quickly, the diverter coils and their driving transistors can fail. Transistors on the auxiliary driver board will short out in a couple of activations on Star Trek if the tieback voltage is not present on the board. If the two Star Trek diverter coils lock on after a game is started, check the violet/yellow wire which connects to the playfield's single drop target coil. Additionally, add 1N4004 diodes to the two diverter coils (banded side of the diode to the coil's power lug), and test the TIP102 transistors on the Auxiliary driver board.
If a transistor shorts on the Auxiliary driver board, this will cause the driving coil to lock-on as soon as the game is turned on. Again on STNG this is very common for the under-playfield diverter coils. With the game off, check the diverter coils first - they should have 7 to 9 ohms of resistance (tested in-circuit, any less and replace the coil). This transistor is Q13 on the 8 driver board runs the sm1-26-600 coil.Don't bother testing the transistor(s) on the Auxiliary driver board. They will *not* test correctly in-circuit. Just replace the TIP102 and it's companion 2N4403. Replace *both* transistors at the same time! Do not skimp here, or you will have to replace both transistors again after the game is turned on! Also test all the resistors related to these two transistors, and the 1N4004 diode (the diode and resistors can be tested in-circuit). Buzz out all traces related to the two transistors also, especially the 50 volt tie-back trace.
Driver Transistor Operation.
As described above, the main driver transistor (a TIP102 or TIP36) completes the coil or flash lamp's power path the ground, energizing it. But there are other components involved too!
Each driver transistor has a "pre-driver" transistor. In the case of a TIP102 (the most common WPC driver transistor), this is a smaller 2N5401/MPSD52 or 2N4403 transistor.
If the main driver transistor is a TIP36c, this is pre-driven by both a TIP102 and a smaller 2N5401/MPSD52 or 2N4403 transistor. The bigger TIP36c transistor is an even more robust than the TIP102, and controls very high powered, high use coils (like the flippers).
Then before even the smaller 2N5401/MPSD52 or 2N4403 pre-driver transistor, there is a TTL (Transistor to Transistor Logic) 74LS374 chip. This is really the first link in the chain. This is what in affect turns on the smaller 2N5401/MPSD52 or 2N4403 pre-driver transistor, which then turns on the TIP102 (which then turns on the TIP36c, if used for the coil/flash lamp in question), and energized the device.
This series of smaller to bigger transistors is done to isolate the hi-powered coil voltage (50 volts), from the low-power logic (5 volts) on the driver board. Also the 74LS374 chip (operating at +5 volts), which really controls the transistors, can not directly drive a high power TIP102 or TIP36c transistor (which is controlling 50 volts).
If ANY of these components in the chain have failed, a coil/flashlamp can be stuck on, and will energize as soon as the game is powered on!
I have a Stuck-on Coil (or Flashlamp), What should I Replace?
A short summary (before reading all the info below). The following procedures will test the driver and pre-driver transistors in question. If either is bad, it will need to be replaced. When replacing either a driver or pre-driver transistor, replace them both (or in the case of a TIP36, replace the TIP102 and smaller 2N5401/MPSD52 or 2N4403 transistor)! A shorted transistor will cause the other transistors in the link to be stressed, and they should all be replaced.
Inside the front cover of the game manual is a list of each coil used in the game. Also listed are the driving transistor(s) for each coil. Use this chart to determine which transistors could potentially be bad. Also use the schematics.
If after replacing the driver transistors the coil/flashlamp is still locked on, then replace the TTL 74LS374 logic chip. The TTL 74LS374 can also go bad (though it is not real common). This can be tested with the diode function of a DMM (red lead on ground, black lead on each leg of the chip) A value of .4 to .6 should be seen for all pins except ground and power.
Also if the new TIP102 transistor is not soldered in correctly, this can cause the TIP102 to short again. This happens becasuse the old TIP is hastly removed, destroying the plated-through holes in the circuit board. After soldering the new transistor, make sure all three transistor legs are connected to their traces. Use the continuity feature of a DMM to test this. Particularly if the center leg does not connect to the 1n4004 diode (trace on the component side of the board), the TIP102 will work for one "fire" and then lock-on during game play and destroy itself.
Also remember to test the resistance of a coil after replacing the driver transistors. If a coil gets hot, it can burn the painted enamel insulation off the coil windings. This lowers the overall resistance of the coil because adjacent windings short together. If resistance gets much below 3 ohms, the coil becomes a "short", and will fry its associated driver transistors very quickly!
