Williams Laser cue: drop target solonoid stays on: fuse blows

zevv

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Williams Laser cue: drop target solonoid stays on: fuse blows

Hello,

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
 
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?
 
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.

This is what's throwing me off - during normal game play, you say the coil is constantly stuck on, yet in the coil test, it behaves completely normally - it goes on/off, and does not cause the higher amperage pull resulting in the fuse blowing?

So you can play normally, the issue occurs, the coil is stuck on. If you power cycle the game - no change; the coil is stuck on. Is this only during game play, or even when it's sitting in attract mode?.

If you then immediately go into the coil test, the coil shuts off, and then behaves normally until you go exit the coil testing and the game is once again in attract mode?
 
no nothing about the board in this game, but if the 6821 is socketed and you have more than one 6821 on the board, swap them and see if the problem follows the PIA

there are testers for the PIA's but its way cheaper just to buy more of them
 
This is what's throwing me off - during normal game play, you say the coil is constantly stuck on, yet in the coil test, it behaves completely normally - it goes on/off, and does not cause the higher amperage pull resulting in the fuse blowing?

So you can play normally, the issue occurs, the coil is stuck on. If you power cycle the game - no change; the coil is stuck on. Is this only during game play, or even when it's sitting in attract mode?.

If you then immediately go into the coil test, the coil shuts off, and then behaves normally until you go exit the coil testing and the game is once again in attract mode?

That's what throwing me off as well. I'm still not sure how to consistently fix the issue, but I expect it has something to do with things cooling down; it's the only thing I can think of now because the issue persists over powerdown, but resolves after some time.

For now I have a magic workaround: I have put a 5 Amp lightbulb from my car in series with the fuse. The idea to use it as an indication for too much current running there for too long, but for some reason this also seems to prevent the situation to happen. No clue why, though.

I'll swap PIA's to see if anything changes, thanks!
 
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