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System 11 Sound Issue

MajesticPinball

MajesticPinball

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Joined
Jan 11, 2018
Messages
2,300
Location
Essex
Alias
James Reed
I've got very loud and annoying vibrating bass hum kinda sound on a Jokerz. During gameplay sounds and music does work however the very loud hum remains. I know System 11 games do tend to hum a little but this is very loud!

I don't have very much knowledge on sound boards as I've never really had to touch them... the 16 or so machines I've owned over the years have never had any sound problems so any advice on what the issue could be would be hugely appreciated!


Thanks guys,
James
 
Sgt GrizZ said:
Does it do it all the time or just when game running?

First port of call.... could be worth tightening down all the boards in the backbox. Really make sure those screws are tight. I recently had a slightly older Williams game making an unholy buzz and that sorted it.

Sent from my D5833 using Tapatalk
Click to expand...
All the time mate, the game was in attract when I made the video, it's a pretty constant noise... Doesn't really change between attract and during a game.

I'll be at the arcade tomorrow so will check all of the bolts, if that solves the problem I'll report back. Thanks Grizz
 
Quick update. Tightened all the bolts holding down the boards and replaced a couple that were missing... Game booted up and some of thr sound effects are there.... No music went into test and it's saying "music failure" I've ordered a replacement YM3012 chip could there also be a ROM issue? What do you guys think?
 
Could be the summing op amp that combines music and speech.
Has one leg come off the crystal?
Change the CAPACITORS. I would start with that before you start swapping hard to find yamaha YM chips.
 
I’d reseat any thing plugged into that board including removing and reseating chips if they are not soldered directly to the board.
Reseat ribbon cables etc...
 
Pick Holder said:
Could be the summing op amp that combines music and speech.
Has one leg come off the crystal?
Change the CAPACITORS. I would start with that before you start swapping hard to find yamaha YM chips.
Click to expand...
Crystal is in good and solid. None of the capacitors look suspicious are there any in particular I should be looking at or should I just replace everything.

Spandangler said:
I’d reseat any thing plugged into that board including removing and reseating chips if they are not soldered directly to the board.
Reseat ribbon cables etc...
Click to expand...
I've reseated all of the socketed chips and the connectors multiple times, doesn't make much difference at all sadly
 
I had what sounds like a similar problem with humming with my Earthshaker a while back. I spoke to Andy Netherwood who said that hum is caused by AC on the DC power supplies, and to test the power supply board DC test points for AC voltage.

It turned out that the -12V DC was showing 10V AC on it - enough to make the amp on the sound board hum. Probable suspect was the 1000MFD capacitor which is meant to smooth the -12V supply and looked damaged, so I replaced that. Made no difference though, but one of the two 7A fuses blew. And the new capacitor exploded.

Then I replaced the bridge rectifier upstream of it, and replaced the exploded capacitor, and replaced the fuse, and that fixed it.
 
Last edited:
Hi, James,

Bear in mind that the audio pcb used in Jokerz is different to other system 11 games, I think it was known as 'Pin Sound 88'. When one of the Jokerz owned by work started this, it turned out the problem was in fact caused by the Cpu/driver board, it stopped once the one fitted (from a Grand Lizard) was exchanged.
 
My BK2K was humming allot I replaced all the caps and the volume pot which made a slight improvement but what got rid of it was adding ferrite cores to the power cables going in and out of the sound board now hardly any hum :)
 
Thanks for the advice gents, has given me a good list of things to try out, will report back soon hopefully with a fixed machine lol
 
Yeah generally speaking, if you've only tightened bolts and you've ended up with a dead board, you're going to be looking at cold solder joints potentially all over the boards - including on passives like capacitors, not just ICs.

That video definitely sounds like 50hz AC is bleeding in somewhere from where it shouldn't be.

System 11 sound is loads of fun except when it comes to electrical isolation. They're just crap for it. Come to think of it... all of System 11 plays a little loosely with electricals. After all, the early ones like to try and catch fire...
 
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