(Topic ID: 30635)

Buzzing light matrix noise on my Williams System 11 Fire! - FIXED


By ChadH

7 years ago



Topic Stats

  • 29 posts
  • 14 Pinsiders participating
  • Latest reply 28 days ago by sataneatscheese
  • Topic is favorited by 10 Pinsiders

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#1 7 years ago

My Williams System 11 "Fire!" had a terrible buzzing noise that would correspond with the light matrix. This was especially noticeable in attract mode with the sweeping/dancing light show. When the light matrix was off, it was almost completely quiet.

I tried swapping sound boards with a known good one. This did not fix it.

I tried powering the sound board with a separate PC power supply. This did not fix it.

I tried unscrewing sound board and letting it float free. This greatly reduced the lamp matrix buzz by about 90%!

So I went to Home Depot and bought some 8-32 nylon screws and nylon washers and now have the sound board screwed in with these. Apparently there was some kind of ground loop happening between the light matrix and the sound board.

#2 7 years ago

Cheap fix for a common problem!

#3 7 years ago

thanks for sharing ChadH

#4 7 years ago

That means there is a part in the circuit that is shorting to the ground. This is a common problem with Williams System 11? Was/is it limited to a certin range of years???

#5 7 years ago

The nice thing is this is a quick test that anyone can do on their noisy game. Just unscrew the sound board and let it hang free. Turn on game and listen.

#6 7 years ago
Quoted from jrrdw:

That means there is a part in the circuit that is shorting to the ground. This is a common problem with Williams System 11? Was/is it limited to a certin range of years???

A lot of sys11 games hum along to the pattern of the light show in the attract mode.

The normal fix is to clean the pads on the back of the circuit boards where they make contact with the metal standoffs that lead to the backbox ground plane.

Then clean the tops of the standoffs themselves.

Finally, make sure that each ground screw is in place along each circuit board in the backbox. After 20 years, it is often the case that a few screws are missing.

#7 7 years ago
Quoted from vid1900:

A lot of sys11 games hum along to the pattern of the light show in the attract mode.

The normal fix is to clean the pads on the back of the circuit boards where they make contact with the metal standoffs that lead to the backbox ground plane.

Then clean the tops of the standoffs themselves.

Finally, make sure that each ground screw is in place along each circuit board in the backbox. After 20 years, it is often the case that a few screws are missing.

But if the problem is a ground loop, then won't doing this must make the ground loop worse?

#8 7 years ago
Quoted from ChadH:

But if the problem is a ground loop, then won't doing this must make the ground loop worse?

You avoid ground loops by keeping all the grounds at the same potential.

So all those standoffs are all leading to the same ground plane; that is the intended design.

But over time connections can corrode and have their resistance increase, components can short or fail and change the path to ground, screws can be lost or loose and change the path to ground.

#9 7 years ago

After reading this thread, I just fixed my horrible buzzing problem on F-14 Tomcat by adding a couple of screws to the main PCB. Thanks for the heads up, OP and Vid1900..

#10 7 years ago
Quoted from tamoore:

After reading this thread, I just fixed my horrible buzzing problem on F-14 Tomcat by adding a couple of screws to the main PCB. Thanks for the heads up, OP and Vid1900..

Excellent example of killing a ground loop by restoring the intended path to ground.

Thanks for the timely addition to the thread.

#11 7 years ago

Just like in any sound system a hum in the speaker is a symptom of a bad ground. I thought I mentioned checking the grounds in the other thread. The term "ground loop" is simply describing a non-completed circuit, (correct me if I'm wrong about that).

#12 7 years ago
Quoted from jrrdw:

Just like in any sound system a hum in the speaker is a symptom of a bad ground.

Many times it can be, especially if it is that "60hz" tone.

I had a big sub woofer that had the loudest hum develop about 6 months out of warranty.

I opened it up and the 2 big caps on the amp circuit board were bulging and leaking. I swapped them out with better quality Panasonic caps rated for higher voltage - and that fixed it nicely.

Quoted from jrrdw:

The term "ground loop" is simply describing a non-completed circuit, (correct me if I'm wrong about that).

A ground loop means that part of the circuit has found a path to ground with a different potential than another part.

#13 7 years ago
Quoted from vid1900:

different potential than another part.

Is that saying that a part is grounding that shouldn't be? A shorted circuit, (layman's term)...

Thanks for the additional info. It really helps when trying to understand electronics and fix our own machines.

#14 7 years ago
Quoted from jrrdw:

Is that saying that a part is grounding that shouldn't be? A shorted circuit, (layman's term)...

Trying to describe it in layman's terms: part of the circuit has found a different path to ground, that has more or less resistance than another path. It does not have to be a shorted circuit, but just another path that is different enough to cause hum (or rolling bars in a video circuit).

In a high powered audio amplifier, oftentimes all the circuit board grounds will come together at a single point, thus all boards will have the exact same ground potential - this is called "star grounding".

If I get really board, I'll draw up a diagram of different ground loop scenarios.

#15 7 years ago
Quoted from vid1900:

I'll draw up a diagram of different ground loop scenarios.

That would be cool. It's hard to trust what's on line. I can normally find 3 entirely different answers to the same question.

#16 7 years ago
Quoted from vid1900:

You avoid ground loops by keeping all the grounds at the same potential.
So all those standoffs are all leading to the same ground plane; that is the intended design.
But over time connections can corrode and have their resistance increase, components can short or fail and change the path to ground, screws can be lost or loose and change the path to ground.

Understood.

But now I just did the same thing on my one other problematic "noisy" pinball machine. My Data East Star Wars was also really loud and buzzy during attract mode. Most noticeably noisy in conjunction with the dancing attract mode matrix lamps and also the DMD.

I, again, removed the sound board and then "floated" it with nylon screws and nylon washers. The buzzing and noise has been reduced by about 90% on this one now.

Before I did this, I tried to screw all boards in tight and check all wire in an effort to chase down the ground loop first. But when all else failed, I tried this method and it worked (twice now).

By the way, one other thing I did on this Star Wars was a bought a new Rottendog power supply. My original power supply was in bad, bad shape. Crazy bad solder jobs over the years and a lot of lifting and bubbling on the circuit board. When I replaced it with a new one, my hum dropped a lot but the buzzy dancing noise that came from the DMD and lamp matrix did not go away. Only after I "floated" the sound board did that go away.

#17 7 years ago

So maybe some cap or resistor has failed over the years on one of the boards and has created another path to ground that you have interrupted by floating your board.

The only way to really know is to use an Oscope and trace back the buzz until you literally find the point it enters the audio circuit.

It could turn out to be a common problem and fix many machines, or it could be unique to your machine and others have to do their own detective work.

I'm just glad you got it fixed, even if we don't know exactly what went wrong where.

8 months later
#18 6 years ago

Chadh>>>> Thanks for posting this. I just picked up a Fire! pin 3 weeks ago and noticed the same problem. I replaced the screws with nylon and problem solved!! Great tip!

2 years later
#19 4 years ago

Just applied this fix to mine. Dramatically better with about 60 percent less noise. Thanks for the tip.

#20 4 years ago

This same fix applies to Bally -32/-50 sound boards. Cracked header pins cause ground isolation / looping issues. The cheater fix sometimes is to insulate the grounds from backbox mounting or. Best fix is to figure out the ground issue. I think this happens on the early bally sound boards because the solenoid voltage (for the amps) and the logic voltage have isolated grounds... somewhat.

4 years later
#21 3 months ago

Going to necro this thread only to mention that this worked perfect for me on my High Speed. Nylon screws and washers cost a couple bucks from Lowes and the hum from the lights went away.

2 months later
#22 55 days ago

Same noise issue . I took out screws and let sound board hang. Still have noise. Switched out another sound board and made sure all screws are on all boards. No success. Ground strap in cabinet is tight. Don’t know what else to try....

2 weeks later
#23 37 days ago

Glad i found this thread. My Grand Lizard has the screeching sound in attract mode that is completely in sync with the playfield insert lights, when they are wiping back and forth. Cant really hear it during play.

All of the screws in the boards are present. I will try cleaning the pads on the boards like vid suggested, and i will try to float the sound board too.

There is a 3 wire cable running from the bottom right of the MPU to the sound card that influences the sound. If that cable gets near the speaker or any transistors, the sound gets much louder.

Will work on it some more tomorrow.

1 week later
#24 28 days ago
Quoted from wrd1972:

Glad i found this thread. My Grand Lizard has the screeching sound in attract mode that is completely in sync with the playfield insert lights, when they are wiping back and forth. Cant really hear it during play.
All of the screws in the boards are present. I will try cleaning the pads on the boards like vid suggested, and i will try to float the sound board too.
There is a 3 wire cable running from the bottom right of the MPU to the sound card that influences the sound. If that cable gets near the speaker or any transistors, the sound gets much louder.
Will work on it some more tomorrow.

Any progress ?

#25 28 days ago

I'm interested in hearing your results too. I have several buzzy System 11 games.

#26 28 days ago

Okay I "floated the board, and that created a very loud humming noise, in addition to the screeching sound. Obviously a step back, so the board got reattached.

There is a cable that runs from J16 on the main board, to J1 on the soundboard, and it plays a major roll in the volume of the screeching sound I am hearing. Again the screeching is only noticeable in attract mode as the playfield lights are wiping back and forth. It is also louder when the majority of those lights are lit.

So when this cable is moved near the speaker, or the transistors on the main board, the screeching gets much louder. So what I have done is strategically routed the cable across the main board in a manner that results in the lowest volume of screeching. So I can still hear it in attract mode, but its as quiet as I can get. I am wondering if that cable were to be lengthened, and routed in a way so it does not cross the main board, would that further reduce the volume of the screeching. If I get any time, I might try this. But thats where it stands.

#27 28 days ago

Is that cable shielded? If it's not, maybe using a shielded cable will reduce it. If it is, maybe a better shield.

#28 28 days ago
Quoted from wrd1972:

Okay I "floated the board, and that created a very loud humming noise, in addition to the screeching sound. Obviously a step back, so the board got reattached.
There is a cable that runs from J16 on the main board, to J1 on the soundboard, and it plays a major roll in the volume of the screeching sound I am hearing. Again the screeching is only noticeable in attract mode as the playfield lights are wiping back and forth. It is also louder when the majority of those lights are lit.
So when this cable is moved near the speaker, or the transistors on the main board, the screeching gets much louder. So what I have done is strategically routed the cable across the main board in a manner that results in the lowest volume of screeching. So I can still hear it in attract mode, but its as quiet as I can get. I am wondering if that cable were to be lengthened, and routed in a way so it does not cross the main board, would that further reduce the volume of the screeching. If I get any time, I might try this. But thats where it stands.

Interesting. Thanks for the update. There is a guy on high speed club thread who had some success with the volume control potentiometer. He posted a video. Wire was causing humming noise. I will try both solutions and maybe shielding.

#29 28 days ago

I traced the humming linked to lights to the grounding of my volume knob. Excerpt from High Speed thread below.

I found the issue that was causing a loud buzzing while in attract mode. It is a grounding issue with the potentiometer (volume knob) itself. I was in the process of switching out the potentiometer (which I did but used too small of one so now it's even louder) when I ran out of butane for my soldering iron. The red and black wires were left unplugged so no sound should be coming through the machine right? Wrong! I have sound at a reasonable level. I'd like to turn it up a little, but it is just fine for my house for now and I will leave it as be until I can get the correct part in.

As a side effect THE HUMMING NOISE WENT AWAY!!! I also discovered that if I touch the black wire to the grounding plate the potentiometer is on, the humming noise comes back. So, if you have issues with a loud humming noise going in concert with your lighting, it is most likely a grounding issue with the speaker wire with a prime suspect being an older poteniometer bent into the grounding plate.

Below is an extremely low quality video describing the buzz and how to possibly fix it.

Thanks guys!

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