(Topic ID: 273994)

Jokerz Hum Solved


By fixintoplay

15 days ago



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  • 30 posts
  • 9 Pinsiders participating
  • Latest reply 8 days ago by fixintoplay
  • Topic is favorited by 12 Pinsiders

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#1 15 days ago

I uncovered a fix that eliminated the annoying hum or buzz in my Jokerz, and I wanted to share this on Pinside. This solution worked on my machine, which doesn't mean it will on every other one. But it offers clues as to what causes it and how to understand it. I have read everything I could find on this phenomenon, not just for Jokerz but for other Williams System 11 titles and could find no conclusive answer on how to address it. The culprit, EMI, or electromagnetic interference, only affects sound (through speakers), but not any other playing or electronic functions. By definition, EMI is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. The challenge is to find the source so you can address it. It requires a disciplined process.

So I created a list of every plausible idea, suggestion, trick, or hint I could uncover on Pinside searches. This gave me a hit list. I found that if one claim worked on one machine, it didn't necessarily work on another. So why not try them all? I enjoy fixing pins about as much as I do playing them. The solution was out there. I was determined to finding it.

I got my Jokerz in the beginning of March 2020, days before the Coronavirus chaos hit the US. The timing couldn't have been better for me. The machine was in average player condition, some minor hacks, new Rottendog power supply, and an NVRAM installed. Most important, it worked. Not 100%, but I was OK with that. It needed me. Before I could power it up, I had to first replace the line cord crushed in shipment. It needed considerable cosmetic care and mechanical repair work, but that would come later. From the first game I played, I noticed the hum. Not too bad. But over time, it got worse and was intermittent. On a scale of 0 to 10 (zero being none, 10 being intolerable) the intensity would vary between 3 and 9. On rare occasions, when I would do work in the back box it would change. Sometimes better, sometimes worse. During play, the flashers and certain light features would amplify the noise. It was near impossible to pinpoint what was causing it. After a few months of playing and restoring, I was determined to kill the hum.

Each time I researched this issue, I created a log. From that, I prioritized a series of steps starting with the easiest first. Plan was, complete each step, play a test game. Here's how it went:

1. Replace the volume potentiometer. One advisor said don't replace it until you try turning it back and forth many, many times and/or clean it with contact cleaner. Over time when not used, carbon crystals form on the wiping surfaces of these devices and can cause static interference. I cleaned and turned it. No effect on the hum. Five minutes. The new pot, which I had already ordered, is a now a spare in my inventory.

2. Remove the four chips on the audio board, clean the pins and reseat them. I used a soft brass bristle brush. Ten minutes. No effect.

3. Rebuild the EMI filter in the power inlet/fuse box on the lower inside cabinet. I learned EMI filters don't last forever. This one was 22 years old. Inside the enclosure is a Corcom 5KV1 5amp EMI filter with a metal oxide varistor (MOV) across its two line terminals. The fuse holder and power line outlet were left in place. I began a new parts list with these two items. Why not? Easy to replace, less than $25. I had the highest hopes for this step.

4. Install a 68 ohm resistor between the two upper speakers. Not sure which post this came from, but I ordered the 70 cent resistor.

5. Install ferrite core snap plugs on cables. This is like the wild west. I had some notions of where to mount these things, but it would be purely experimental based on logic and assumptions relative to the effects of EMI from cables. Think how many linear feet of cable there are in these machines. This would be a needle in a haystack. I added a batch of four different sizes to my parts list based on the various sizes of the machine's bundles. Photo shows what they look like. Actually quite affordable. They're used everywhere: computer power cords and many other electronic equipment. Their function is to limit EMI in sensitive devices. And they work in both directions. Pretty cool. They snap and unsnap easily, which greatly simplifies experimenting on a variety of different cable locations.

6. "WMS Service Bulletin (PDF), "subject: Jokerz Audio Hum". I couldn't find any posts or comments where this factory recommended alteration actually reduced the hum. It had not been performed on my machine, but I added it to the list anyway. I put the parts on the order. This involved some board work, which I can handle.

7. Replace the line of capacitors C60-C67 , as well as the C30 capacitor on the CPU. This involved removing the CPU from the machine. Whoa, I can do that, but that's an involved project. I added the components to the parts list and moved it to the last step on the to-do list.

8. Replace lower bridge rectifier BR1. This was recommended in a few posts, but a trusted advisor said he'd never seen any case where the replacement of a bridge rectifier had any effect on EMI. It was already on order, so I moved this priority to the bottom.

9. Just for good measure, I ordered 2 new ribbon cables in the parts order: the 26-pin from the display board to the CPU, and the 20-pin from the CPU to the audio board. This had no effect on my issue, but it should be done anyway. I installed them. Nice and snug.

The Corcom EMI filter arrived first, so I rebuilt the enclosure with the new parts. Photo shows the original parts removed. Zero effect on the hum. Hopes were dashed.

Next to arrive were the ferrite core snap plugs. It gave me a chance to try them out on a few cables. I wish I had ordered these bad boys first. I figured if the problem was speaker hum, I'd start there. I targeted the largest cable bundle closest to the first speaker in the back box, which I thought was a logical place to start. It always bothered me that the speaker wires were just laying loosely in the area and not properly routed. Photo shows. There appeared to be some hacks for the ground wires, too. So I worked those speaker wires into the large cable bundle in same ferrite core. One technical paper I found recommended looping the wires through the ferrite core more than once for better effect, so I did that to the speaker wires, as well. The picture shows what the assembly looks like, before and after.

Then I powered up the machine and I started a game.

The hum is gone. Zero. But I remain skeptical. Every time I fire up the machine and play a game, I expect the buzz to come back with a vengeance, but so far it hasn't. About 20 games so far. Pure magic. My hope is that this information helps someone else with audio and speaker hum issues. But most of all, I hope it keeps working! (But if it doesn't, I still have 4 more steps to try and the parts to go with it!)

EMI Filter w MOV (resized).JPGFerrite Core Plugs (resized).JPGB4 ferrite3 (resized).JPGDSC08552 (resized).JPG
#2 15 days ago

Thanks for the write up! Interesting solution and makes me wonder if this is the root cause, or a good treatment of the symptom, and in what circumstances it would help other speaker hum issues.

#3 15 days ago

I just picked up my first pin on Sunday which happens to be Jokerz. I will definitely be trying this. I have bad crackling in the sound FX but speech and music is clear other than the very loud hum. I’m listening to it right now while in the basement. Thanks for this post!

#4 15 days ago

Good luck with your new dependent! It’s a great game.

#5 15 days ago

I had a Ferrite laying around so I installed it but it didn’t make any difference on my hum. I don’t believe mine has the field update done to it either so I wonder if it’s a combination of things that needs to be done to remove the hum?

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#6 15 days ago

Jay -I thought the solution he mentioned was wrapping a loop of the audio cord around the ferrite bead. The ferrite around the cord as you show did not do anything.

Out of curiosity, can you try that?

#7 15 days ago

I thought I installed mine exactly as he showed in his picture. He has the ferrite around the bundle of cables nearest the speakers and I have the audio cable wrapped around And through the ferrite like he does. It looks the same as his pics but I will double check.

#8 15 days ago

It looks like Jay has it right: the speaker wire looped thru the ferrite twice. That’s disappointing. I would try addIng another one up or down the line. I put these other places, too, which made no difference before this attempt. (One on each side of the EMI enclosure.) There’s a reason why mine worked. Try buying new ones and install them at various locations. They’re magic beans. Don’t give up yet.

#9 15 days ago

I was thinking the same thing. This is a ferrite I had laying around from the power cord of a old Plasma TV. I wonder if different size ferrites might make a big difference. There is a small electronic component place close to me that should have some if they are opened back up yet. I might stop in there at lunch and grab some different sizes.

#10 15 days ago

Look at my photo again. All speaker wires lead directly away from the solder tabs and travel away from the speaker’s magnet, not past or along side of it. Trying rerouting yours per my photo. Worth a try.

#11 15 days ago

I’m referring to the after photo, not the before shot! Should mention that, haha.

#12 15 days ago

FYI. Here are the ones I ordered from Amazon. Had them in 3 days.
amazon.com link »

#13 15 days ago

We did the WMS issued service bulletin to my dad's Jokerz. It helped, but not all the way.

All of the system 11 games, and de/sega really for that matter, have some level of audible hum when the room is silent. Seems like the hum/noise comes from the feature lamps. Makes sense ferrite would help.

#14 15 days ago

The overdriven amp thing with the resistor / pot fix (on the mpu) definitely helps a LOT with whitestar.

#15 15 days ago

I have a significant update. I was sure there was another source of interference that was not showing up on mine. So I removed the ferrite arrangement I had installed. The buzz returned, which gave me a chance to experiment with plugs on other areas. I spent several hours on this today. And then I remembered one post about the draw poker motor. I unplugged it, and the hum disappeared. I was certain it directly causes the hum and believe I have isolated the source. So I reinstalled the ferrite as I had before, and WTF, my hum was back. I was crushed. I could hear those jokers laughing at me. I installed more ferrite plugs on both sides of the poker motor cables input/ouput. No effect. I added more plugs on every section of cable bundles from there back to the light board and inside the back box. No effect. So I removed the draw poker motor assembly and took pictures. What would cause this device to do this? Unlikely it's the motor because it only runs briefly during draw poker mode with no hum. It has to be an inherent design flaw in the board because this is a unique issue with all Jokerz. I did notice what looks like corrosion or leakage on U1. Could that be a problem? I'm out of ideas.

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#16 14 days ago

Shield the motor board and cabling? Change the wire routing? Does the hum change if you open/close the backbox door?

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#17 14 days ago

That's a stepper or servo motor. They can be used to hold a stationary position without a brake. If it's used that way here it is actively outputting voltage to the motor all the time even if whatever it's driving is not moving.

#18 14 days ago
Quoted from barakandl:

Shield the motor board and cabling? Change the wire routing? Does the hum change if you open/close the backbox door?[quoted image]

Backbox door open or closed, there is no change in hum.What is that shield material called? Is it metallic?

#19 14 days ago

Here's a photo of U1 on the opto control servo motor board pulled apart. Does this look familiar? Looks like decomposition or heavy leakage of some sort from heat. It's the IC voltage regulator 7805. I ordered a new one. Maybe this is the cause? I'll find out and post. Comments welcome.

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#20 14 days ago
Quoted from fixintoplay:

Here's a photo of U1 on the opto control servo motor board pulled apart. Does this look familiar? Looks like decomposition or heavy leakage of some sort from heat. It's the IC voltage regulator 7805. I ordered a new one. Maybe this is the cause? I'll find out and post. Comments welcome.
[quoted image]

The white stuff is heat sink compound. It helps the heat sink draw heat away from the transistor.

#21 14 days ago

I have several other heat-sink-mounted transistors in this machine there's no evidence of compound. This one just a sloppy job maybe? The screw that secured it was damaged, so it's been worked on before. I'll replace it anyway since I'll have the part. Thanks for the info.

#22 14 days ago

Some background checks show it's called thermal paste, and it doesn't last long. Needs to be cleaned off and reapplied depending on operating conditions (mainly temperatures), otherwise component life drops measurably. The residue on mine indicates it is not factory, was over-applied, dried out and lost its usefulness. This is an important item to keep on hand. Thanks again for contributing jscaptura. Added it to the learning curve...

Quoted from jscaptura:

The white stuff is heat sink compound. It helps the heat sink draw heat away from the transistor.

#23 13 days ago

Here's a more scientific discussion and test data on thermal paste.

https://www.gamersnexus.net/guides/3346-thermal-paste-application-benchmark-too-much-thermal-paste

#24 10 days ago

I wanted to update this thread. The title should read: Jokerz hum isolated (not solved - yet). I finished all the measures on my hit list, plus a few more. Nothing lasted for more than a game. When I unplugged the draw poker opto board connector (output) it disappeared for good. I removed that assembly, replaced the U2 voltage reg with thermal paste and reflowed the 2 header pins in case there was a cracked solder joint and added ferrite plugs to both cables. When that had no effect, I crafted an "EMI shield" from an aluminum can and encased the draw poker motor to see if it was the source of the EMI radiation. Also no effect. The photo shows the only way I have found to permanently stop the BUZZ, which more accurately describes the sound on mine. The draw poker display and scoring work fine this way, just no spinning cards.

If anyone has any other ideas or suggestions, please chime in.

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#25 9 days ago
Quoted from fixintoplay:

I wanted to update this thread. The title should read: Jokerz hum isolated (not solved - yet). I finished all the measures on my hit list, plus a few more. Nothing lasted for more than a game. When I unplugged the draw poker opto board connector (output) it disappeared for good. I removed that assembly, replaced the U2 voltage reg with thermal paste and reflowed the 2 header pins in case there was a cracked solder joint and added ferrite plugs to both cables. When that had no effect, I crafted an "EMI shield" from an aluminum can and encased the draw poker motor to see if it was the source of the EMI radiation. Also no effect. The photo shows the only way I have found to permanently stop the BUZZ, which more accurately describes the sound on mine. The draw poker display and scoring work fine this way, just no spinning cards.
If anyone has any other ideas or suggestions, please chime in.
[quoted image]

Just some ideas..........

Try changing the route of the wire involved with noise and/or shielding it. With audio stuff, like the coin door volume pot in a wms game(sys 6 at least). They use an earthed shield around the those wires going from the sound board to the volume pot at the coin door. Presumably so noise does not get into that wire run.

Different system all together but I had a sound card that sounded fine on the test fixture but hummed in real games with a different PS. The main 12v filter cap on the sound board was not doing a good job and replacing it cleared out the hum. Make sure filter caps are in good shape on the power supply and sound board.

Make sure the backbox ground is good and the boards are screwed down well. Other system 11 games hum is exacerbated when the main board if not screwed down to the earth grounded backbox sheet.

#26 9 days ago
Quoted from barakandl:

Just some ideas..........
Try changing the route of the wire involved with noise and/or shielding it. With audio stuff, like the coin door volume pot in a wms game(sys 6 at least). They use an earthed shield around the those wires going from the sound board to the volume pot at the coin door. Presumably so noise does not get into that wire run.
Different system all together but I had a sound card that sounded fine on the test fixture but hummed in real games with a different PS. The main 12v filter cap on the sound board was not doing a good job and replacing it cleared out the hum. Make sure filter caps are in good shape on the power supply and sound board.
Make sure the backbox ground is good and the boards are screwed down well. Other system 11 games hum is exacerbated when the main board if not screwed down to the earth grounded backbox sheet.

Thanks. You gave me an idea about the volume pot: it's the main thoroughfare for all sound to the speakers. So I snapped a ferrite core ring around those two wires, and the buzz has disappeared, for now. Six games and counting. If another Jokerz owner could try this trick on his machine, that might provide confirmation. If not, I'll keep trying. No conclusions yet. I don't trust those jokers.

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#27 9 days ago

I've been following the thread but too busy to test any of these 'fixes' on my machine. Now that you've put the ferrite on the volume wire, what if the problem is as simple as the volume pot itself? I've restored some 1970's Marantz receivers in which all the pots are notorious for causing terrible scratchy noises due to oxidation in the pot. On turntables it is the pitch pot and RPM is not consistent. At any rate, I have a bottle of Deoxit at home and will give my Jokerz a spray to see what happens. Looks like Deoxit treatments to volume pots has been discussed elsewhere on Pinside, too.

#28 8 days ago

The buzz in my Jokerz is gone. For me, the problem is solved. To verify, I removed all 7 ferrites I had placed throughout the machine and started a new game. Buzz was back. Immediate. Agressive. If the old pot is responsible, how did the ferrite get rid of it? I tracked the pot's two wires (red and red/black trace) back to the sound board. They are not the source of the EMI, but merely a pathway. They run right across the left speaker's huge magnet behind the display -- the likely source of the EMI. I considered rerouting the wires, but why bother if the ferrite eliminates it? I'm not suggesting anyone try all the other "fixes" I documented -- that's why I did all the work to eliminate them. If you want to kill the annoying buzz, try a ferrite on that pair of wires. It's too easy not to. I placed one at the pot, one at the sound board connector and one where it passes the magnet. Tested again. Buzz is gone. This explains why I had a false-positive for a few games in my original post: the first large ferrite I put on a fat cable bundle behind the display rested (unintentionally) right between the pot wires and the magnet and blocked the EMI, then fell away when I went back in.

I hope it works for someone else.

#29 8 days ago

This is great info, thanks for taking the time to document it thoroughly. I was actually thinking of using ferrite beads to try eliminating noise from some EL wire project i was working on. I'm gonna order a variety of sizes and try them out.

Thanks again, good work!

#30 8 days ago
Quoted from barakandl:

Just some ideas..........
Try changing the route of the wire involved with noise and/or shielding it. With audio stuff, like the coin door volume pot in a wms game(sys 6 at least). They use an earthed shield around the those wires going from the sound board to the volume pot at the coin door. Presumably so noise does not get into that wire run.
Different system all together but I had a sound card that sounded fine on the test fixture but hummed in real games with a different PS. The main 12v filter cap on the sound board was not doing a good job and replacing it cleared out the hum. Make sure filter caps are in good shape on the power supply and sound board.
Make sure the backbox ground is good and the boards are screwed down well. Other system 11 games hum is exacerbated when the main board if not screwed down to the earth grounded backbox sheet.

As barakandI alluded to, shielded cable may offer a higher level of EMI noise protection over ferrite rings in audio runs, but it would obviously involve more work in terms of rewiring and rerouting. And it may have to be grounded or earthed at one or both ends of the run. I may decide to do this and use the ferrites to help hunt down and isolate cables that would benefit from shielding. For those who might be interested here's a Mouser link:
https://www.mouser.com/Wire-Cable/Multi-Conductor-Paired-Cables/Multi-Conductor-Cables/_/N-9ms9i?P=1z0t1rpZ1yyf3fu

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