Qbert Knocker

brokentoken

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I'm having trouble with my knocker--it fires once at power on, but doesn't work during game play. I just replaced the coil and sleeve. Other observations:

* Dip switch 6 on the mainboard is on
* Fuses are good
* Voltages all look right
* Soundboard works, including speech

Any ideas of what to check next?
 
Could be a bad transistor on the main board. Location Q2 2N6044. If you dont have one, steal it from Q4...that one is unused.
Dezbaz is correct. The 30v feeds the soundboard and knocker. Since your sound is working you know the 30v line is good. The knocker should have +30vdc at all times and its ground is switched with transistor Q2.
 
I'll try the transistors next.

Although, I just remeasured the voltage--I'm getting 30vdc at the power board, but only 24vdc at the knocker. That should still be sufficient to drive it, shouldn't it?
 
The way the knocker is set up, you get 30v at one side of the knocker, so if you are getting 24v at the board, that means the knocker is getting 6v (30 - 24)

But I am sure the knocker circuit is just a (less than 1 second) pulse, IE it doesn't stay on, you may just be reading the voltage through the knocker, as opposed to in it's energized state.

That's the nature of electricity.

If the coil is OK, if no current is flowing through it, there will be no voltage drop (Ohms law V=IxR, or 0 Amps x 4 ohms - guess, equals 0), so the same voltage will be felt either side.

The fact you are getting 24V means you have some current flowing.

That makes no sense why there is 24 volts instead of 30v

Maybe your transistor is partly turned on. The transitor could be faulty or the circuitry driving the transistor could be faulty
 
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It is fairly common for the Q2 transistor to fail. Like I said, I would check the filter board solder joints first then then transistor.
 
similar probs with a qbert - can someone please confirm when the knocker is supposed to activate ?

is it when coily jumps over the edge ?
 
thanks dez! was almost right then, could hear a brief bit of static fromt e speaker thats it!

You might want to check and make sure the plunger is free in the coil. A little static and a wave in the monitor is typical when the knocker activates. Sounds like you might just have a mechanical issue.
 
Update: it did turn out to be Q2. I swapped out Q4 as Riptor suggested, and we're back in business.
 
Very common failure.
Pssst...you can use a 2N6045 in place of the 2N6044. Cheaper and easier to find and if I recall its a little beefier.
 
Thanks for all the advice, Riptor (and for the parts, too--I bought the sound amp, soundboard cap kit, and the new knocker coil from you!)
 
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