(SOLVED) Jokerz REALLY loud feedback noise (Not the normal Jokerz hum)


By Oldschool77

1 month ago


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  • Latest reply 3 weeks ago by stoptap
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#1 35 days ago

So about a month ago while sitting in attract mode for about an hour my Jokerz suddenly let out a deafeningly loud feedback type of hum (It sounds like in back to the future when Marty cranked up the amp at Doc's house in front of the huge speaker before plugging in the guitar). I killed the power, cycled power a few times and then it went away. No issues after that, everything was fine. Yesterday i powered it on and it did it again, this time from initial power on. I could still hear the normal boot up "bongs" faintly in the background, and the game sounds are playing in the background as they should, but the deafeningly loud hum is back. This time it wont go away. I tried re-seating everything, checking grounds, etc, nothing made a difference. I don't wanna just throw parts at it. I checked the sound board caps with my multi meter (On the board, which i know isn't preferred or 100% accurate) and 90% of them were within tolerances, but a few were WAY off. But again, i realize that to test caps correctly i have to remove them. At that point I'll just replace them all since it's cheap and easy enough to do.

Anyone have any suggestions where to start looking? Will bad caps cause this insanely loud feedback? Rectifier?

And i want to stress again this IS NOT the normal Jokerz hum.

#2 34 days ago

OK little update.....

Again, trying to resist the urge to throw parts at issues of which I'm unsure if they'll fix, AND resist the urge to freak our assuming it's my unobtanium Jokerz sound board that is the culprit, i swapped power supplies with my Taxi (both the same) and the issue went away. At the same time the issue appeared in my Taxi (about 1/4 as loud, but still obviously there, remember Taxi has a different sound board so probably different/less load requirements from the bower board).

So my guess is there is something up with my Jokerz power board. I took voltages at all the test points on both boards and they seemed to more or less match each other. So I'm going to go ahead and do the rebuild kit which is only caps, from Big Daddy (GPE was out of stock) in hopes that takes care of things. Worse case it doesn't fix it, but it'll have all new caps now which it's probably due for anyways.

#3 34 days ago
Quoted from Oldschool77:

OK little update.....
I took voltages at all the test points on both boards and they seemed to more or less match each other.

Did you only take DC voltage measurements, or did you also measure AC voltage ripple?

#4 34 days ago
Quoted from wayout440:

Did you only take DC voltage measurements, or did you also measure AC voltage ripple?

DC only (I only did the test points), How do i measure ripple (Would bad caps come into play here at all?)

Sorry for my ignorance, I'm "decent" at troubleshooting, but i don't normally run into more then the obvious stuff that's bad like bad/locked on transistors, or bad diodes and caps on all the pins I've had over the years.

#5 34 days ago

You can just set your meter to the AC setting and measure with your probes in the same places that you used to measure the DC voltage. This can also be viewed & measured with an oscilloscope. A failing capacitor will produce an abnormally high AC ripple. Depending on the severity, it may or may not also affect the DC voltage. Temperature can affect it as well, so try the measurement immediately on power up when the components are cool, and also after some run time when the components have warmed up.

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As far as the problem you have, it might not even be a power supply capacitor problem, but could be a cap elsewhere.

#6 34 days ago
Quoted from wayout440:

You can just set your meter to the AC setting and measure with your probes in the same places that you used to measure the DC voltage. This can also be viewed & measured with an oscilloscope. A failing capacitor will produce an abnormally high AC ripple. Depending on the severity, it may or may not also affect the DC voltage. Temperature can affect it as well, so try the measurement immediately on power up when the components are cool, and also after some run time when the components have warmed up.

As far as the problem you have, it might not even be a power supply capacitor problem, but could be a cap elsewhere.

Awesome, thanks I'll try this to nite!! How high is abnormally high? And if it was a cap elsewhere i would think the problem wouldn't of moved with the board when i tried in in my Taxi (and visa versa), but I'm sure anything is possible!

The heat thing makes sense. The first time it did this it was on for a good hour, and when the noise happened it sloped up in volume for about 5 seconds until it maxed out and stayed at a constant blaring volume.

#7 34 days ago

This is one spec that is not usually well defined or well published. Usually, anything below about 500 mV AC is o.k., but when it starts getting above 750mV AC is probably a good sign of filter cap problems. This is mostly true for the regulated and filtered voltages such as for the logic. Unregulated voltages such as solenoid supply often have very wide specs, they might be filtered with a simple single cap and no regulation.

Remember, this is probably not your problem - but it helps to know and be reassured by measurement that your power supply voltages are good.

#8 34 days ago
Quoted from wayout440:

This is one spec that is not usually well defined or well published. Usually, anything below about 500 mV AC is o.k., but when it starts getting above 750mV AC is probably a good sign of filter cap problems. This is mostly true for the regulated and filtered voltages such as for the logic. Unregulated voltages such as solenoid supply often have very wide specs, they might be filtered with a simple single cap and no regulation.
Remember, this is probably not your problem - but it helps to know and be reassured by measurement that your power supply voltages are good.

Awesome, thanks for clearing that up!!!!

Is there anything else that typically goes on these power supply boards? I haven't seen much documented other then replacing the caps. And none of the rebuild kits include anything other then caps.

#9 34 days ago

I had a severe hum on my Jokerz and it was caused by a failed bridge rectifier. Same thing as the filter caps really but more drastic.

#10 34 days ago
Quoted from stoptap:

I had a severe hum on my Jokerz and it was caused by a failed bridge rectifier. Same thing as the filter caps really but more drastic.

Yeah that's kinda where I'm thinking of going next if this doesn't help. My Taxi already had it's rectifier replaced by a previous owner which i thought was interesting.

#11 33 days ago

OK so I took the AC readings on Jokerz power supply board and it was 1.43 VAC. All three test points were more or less the same. I checked my taxi and it was at about 380 MV. So hopefully the caps will fix this.

#12 33 days ago
Quoted from Oldschool77:

OK so I took the AC readings on Jokerz power supply board and it was 1.43 VAC. All three test points were more or less the same. I checked my taxi and it was at about 380 MV. So hopefully the caps will fix this.

Sure sounds like it, good luck!

#13 33 days ago
Quoted from wayout440:

Sure sounds like it, good luck!

Thanks!

#14 30 days ago

Well recapped the board, and it helped a tad. I'd say the hum is about 70% as loud as prior to recap. The AC ripple is "in spec" now, but it's still insanely loud. Luckily i have my fully functioning Taxi right next to it with the same power board. And as i mentioned before, when i put the Taxi power board in the Jokerz the Jokerz works just fine. So i feel like i can rule out anything other than the power board.

So at this point, unless someone has any suggestions of where else to check on the board, I'm going to power up both games up, without the sound boards connected, and compare voltages all over both boards until i can isolate another component that isn't consistent with the Taxi's power board.

Also...how do i know if the rectifier is bad? Would it show up on the test points?

#15 30 days ago
Quoted from Oldschool77:

Well recapped the board, and it helped a tad. I'd say the hum is about 70% as loud as prior to recap. The AC ripple is "in spec" now, but it's still insanely loud. Luckily i have my fully functioning Taxi right next to it with the same power board. And as i mentioned before, when i put the Taxi power board in the Jokerz the Jokerz works just fine. So i feel like i can rule out anything other than the power board.
So at this point, unless someone has any suggestions of where else to check on the board, I'm going to power up both games up, without the sound boards connected, and compare voltages all over both boards until i can isolate another component that isn't consistent with the Taxi's power board.
Also...how do i know if the rectifier is bad? Would it show up on the test points?

I'd change the bridge rectifier on the power board. Cheap and easy to do.

#16 30 days ago
Quoted from stoptap:

I'd change the bridge rectifier on the power board. Cheap and easy to do.

OK I'll give it a shot. Thanks!

#17 29 days ago

So i now am betting on the Bridge rectifier....not sure how i missed this the other day but all my voltages at all the pins on each board are spot on with both games except for +12VDC, on the Jokerz power board I'm getting 10.7VDC, and on Taxi I'm getting 12.2VDC. Those readings are taken with both boards in the Jokerz just to continue to rule out outside influences of the Taxi VS Jokerz. the new BR comes in tomorrow, so fingers crossed!

#18 27 days ago

Replaced the rectifier and all is good now, thanks for all the help!!!

On a side note.....I'm only at around 11.4VDC.....is that within acceptable limits, or should i worry that something else may be on it's way out too? Everything plays and sounds normal (as normal as it can be for Jokerz lol)

#19 27 days ago
Quoted from Oldschool77:

Replaced the rectifier and all is good now, thanks for all the help!!!
On a side note.....I'm only at around 11.4VDC.....is that within acceptable limits, or should i worry that something else may be on it's way out too? Everything plays and sounds normal (as normal as it can be for Jokerz lol)

Leave it be mate. It will be fine.
Told ya about the rectifier Don't know what it is about Jokerz (probably the one of a kind sound board) but it is very sensitive to ac ripple.
Great that you have fixed it. Simple, but fun game.

#20 27 days ago
Quoted from stoptap:

Leave it be mate. It will be fine.
Told ya about the rectifier Don't know what it is about Jokerz (probably the one of a kind sound board) but it is very sensitive to ac ripple.
Great that you have fixed it. Simple, but fun game.

Thanks! Will do! And i agree. When i put the power board in my Taxi, there was a little bit of hum, but barely noticeable.

Yeah Jokerz is fun, my kids love raising the drawbridge and getting the super easy multi ball! If it was my only game I'd probably get bored, but the family likes it, and it's a really really (Python!!!) nice looking game so that's worth it to me!

#21 26 days ago
Quoted from Oldschool77:

Thanks! Will do! And i agree. When i put the power board in my Taxi, there was a little bit of hum, but barely noticeable.
Yeah Jokerz is fun, my kids love raising the drawbridge and getting the super easy multi ball! If it was my only game I'd probably get bored, but the family likes it, and it's a really really (Python!!!) nice looking game so that's worth it to me!

Jokerz was the first game I bought so it has a special place in my heart. I actually know where it is and I could buy it back if I wished but I am all modern Sterns these days.

I LOVE the music on Jokerz when you get a high score.

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