(Topic ID: 178471)

Williams Laser Cue (1984) drop target selonoid: fuse blow

By zevv

7 years ago



Topic Stats

  • 8 posts
  • 3 Pinsiders participating
  • Latest reply 7 years ago by frunch
  • Topic is favorited by 2 Pinsiders

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#1 7 years ago

Hi,

I've got my 1984 Williams Laser Cue back after storage for 7 years, but the solenoid fuse blows after a few minutes of play.

Playing with Fluke connected to solenoid fuse to measure current, what usually happens:

- The game starts up normally, game starts. Fluke measures 0A

- All solenoids work as expected: drop targets are restored to up state and game starts. Fluke measures 0.160A in rest, with few Amp spikes when solenoids are active.

- After playing a few rounds fluke shows continuous current of 4.5 amp and fuse blows shortly after.

In this state, drop target 1 is up, the 2 to 5 are down, and the solenoid for target 1 is powered all the time. Disconnecting 2J11 removes the load, so the problem is somewhere on the bottom board.

Powering off / on does not fix. First drop target is restored but the solenoid keeps active, causing the high current.

Entering solenoid test shows normal results: all solenoids are activated for a short period.

Not sure where to look - the problem does not seem to be electrical or mechanical since the normal solenoid test runs as expected. The problem is that the software keeps the solenoid active for too long for some reason. The switch on the backdrop seems to work OK measured DC, still need to connect a scope to see if it works normally in the scan matrix.

How does the software decide how long to activate a solenoid; does it expect feedback from the switch to see if the backdrop is acually going up, and does it keep current flowing as long as it is down?

Any help very much appreciated.

Thanks,

Zevv

#2 7 years ago

It's probably not the software if the rest of the game is still working while the coil is stuck on. Probably a driver board issue or a bad transistor that's sticking on once it warms up enough. Do you have any other system 7 driver boards you could try? Are all the screws in the corners of the board?

#3 7 years ago

No other boards available unfortunately. All screws are in (why, ground?).

I'll bring in the scope tomorrow to see if the transistor is driven by the CPU.

Thanks!

#4 7 years ago

Sometimes you get weird solenoid issues if you don't have all the ground screws in.

#5 7 years ago

I just checked the levels and it seems that the solenoid transistor is actually being driven by the 6821 PIA (IC5/PA2). Is this a known symptom of a know problem, or do I need to bring in a logic analyzer to see if this pin is actually driven from the CPU?

#6 7 years ago

Does the coil in question activate/lock on the moment you turn the game on?

Whether it fixes the problem or not, I'd suggest replacing the TIP122 (and the 2N2201 pre-driver transistor) associated with that coil on the driver board. Many suggest replacing the TIP122 with the 'more robust' TIP102. Even if it doesn't fix the problem, the parts are probably due to be changed because of the stress of the coil being locked on. And if that doesn't fix the issue, you may need to start logic probing the chips behind the TIP122. There's typically a 7408, and then the PIA.

Good luck!

#7 7 years ago

No, it only locks up sometimes after a few games. I checked the transistor and the pre-driver, but those are ok. Measuring the PIA shows that the output on the PIA is actually high.

I have no spare PIA's lying around so I'll swap with the lamps PIA to see if that changes anything.

Thanks.

#8 7 years ago
Quoted from zevv:

No, it only locks up sometimes after a few games. I checked the transistor and the pre-driver, but those are ok. Measuring the PIA shows that the output on the PIA is actually high.
I have no spare PIA's lying around so I'll swap with the lamps PIA to see if that changes anything.
Thanks.

Looks like you probably nailed it. Replacing the PIA should fix it, I think. Keep us posted!

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