(Topic ID: 254107)

[SOLVED] STTNG 8-Driver Insanity

By Brentd27

2 years ago

Topic Stats

  • 10 posts
  • 6 Pinsiders participating
  • Latest reply 2 years ago by LTG
  • Topic is favorited by 1 Pinsider


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#1 2 years ago

Working on a Star Trek The Next Generation machine and having hell with that 8-Driver. Every time I start the game, the subway & drop target solenoids work fine in test, but after starting a game, a one or more of the right side transistors always shorts to ground and pops F103. The transistor for the little drop target knock down coil almost always shorts. Sometimes another random transistor will short as well. I've already done the following:

Replaced drop target knock down coil
Verified all mechanisms move freely by hand.
Tested ribbon cable
Fixed diode tie-back
Added input pull-down resistors to 8-Driver
Replaced all 2n4403 pre-drive transistors
Replaced 74als576 chip
Reflowed solder on all connectors on the 8D board
Added individual diodes to 2 subway coils, & drop target up & down coils.
Ran new wires from 8-Driver to sw & dt u/d coils.
Unsoldered all 4 coils and verified resistance matched coil chart.
Replaced all TIP102s & diodes on 8-D board multiple times.

I checked voltage at F101, 102, 103, 104, &105. Dc voltage reads ~65V. Grasping at straws, I set meter on AC and got a reading of ~ 175V at all 5 fuses. None of the others are blowing, though. Only F103, and no other transistors are shorting.

At this point, I don't believe the 8-Driver itself is the problem. It's getting a voltage spike from somewhere that is shorting the transistors.

What am I overlooking?

#3 2 years ago
Quoted from Hammerhead:

Give this a read. After melting a few coils and blowing transistors on the 8-driver board, I did this to my STTNG and never had an issue since.

Already did that before adding individual diodes to each coil. Didn't help.

#7 2 years ago
Quoted from Pin_Guy:

Any chance you have or had one of the coils wired backwards in respect to the coil diode? If you do, or even did at some point, this would explain the issues you are seeing.

When I added the diodes to the coils, I made sure that the banded sides are all connected to the lug with purple/green wire (common power for all 4 coils). Quadruple checked them with a meter to make sure none were banded wrong by some weird chance.

#8 2 years ago
Quoted from dsuperbee:

Pulled traces on the board would also cause this.

There are some damaged traces on the board, but I have run wires to replace them, and did continuity checks to be sure they were good and routed properly.

#9 2 years ago

Ok, so future reference, I noticed this evening that the 8-D issue came up every time the bottom diverter fired. I replaced the coil and diode with a similar strength coil I had on hand, and the problem disappeared. (Original coil was ae-25-1000. Replaced with AN-26-1200 with diode.). Original coil is rated 7 ohms, and tests 7.5 out of the machine. So, no clue why it was causing problems I played for 2 hours after coil swap with no issues.

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