This video explains the noise you're hearing as "dirty electricity." You can see this at 5:30. You hear the normal 60Hz sine wave but also some static if you listen closely.
It's obviously a filter capacitor with the high level of capacitance and if it's not filtering properly (dried up if it's an electrolytic capacitor) then it will not absorb this noise and pass it through to the audio amp.
Why would a bridge rectifier be problematic? It will put out the same dirty power that is fed into it from the transformer, which in turn gets its dirty power directly from the wall. This noise in general is what line power sounds like. The normal 60Hz hum plus a lot of line noise caused by power lines picking up other sources of radiation, radio frequencies, etc. The key here should be to feed the amplifier with clean DC power, and re-capping the sound board does this by conditioning the pulsed DC power coming from the rectifier.
castlesteve I don't see any standard-sized rectifiers on the driver board, is this a small wafer-style rectifier? Where is it and what is it labeled as? I can't find anything in the CPU board schematics other than a -12v connection to CN17-8 that doesn't seem to go anywhere. I do, however, see a voltage regulator on the -12v side of the sound board, is this what you meant?
Someone just posted this, claims a new DMD solved his problem. But it's a Williams game, not Data East.
Chad can you get a picture of that area? Either it has somehow broken off or it was never stuffed from the factory (most likely the latter). If this is that case that might explain your problem, according to castlesteve, who says missing +12v would cause it.
Wow! So that means the X-Pin power supply isn't providing a clean voltage source either. Might want to check that out Brett and do some testing. Our Data East supplies and dropping like flies and we're down to just one working original. Would be really nice to have no hum when we order replacements!
You need to look at that 12v wave on the scope. I'm sure it's a mess.
I thought a ground loop was caused by components having different ground potentials and instead of that current discharging through a ground source it dirtied up the normal circuit lines and caused problems. But you guys have a point.
Did that regulator fail under stress or did you drop something on the board? Other people with this issue should check this component on their sound boards to see if it has failed like this.
Back to the ground loop issue though, I'm starting to "get it" now. Basically this means the sound board has more than one path to ground which completes a circuit and it's picking up noise from the other boards? Where would the second path to ground be besides the ground plate? Found a couple of videos if others are having trouble understanding:
Quoted from robertmee:
The paths to ground are likely numerous. You have the ground plate as mentioned. You also have interconnects that carry grounds between boards where other boards are grounded. You also have the main power distribution which is grounded to your wall outlet and the ground braid in the game.
The ground plate isn't connected to the ground braid? So really what needs to be done is remove all connections to ground but one (the ground braid) and that should solve it?
Quoted from robertmee:
Both these boards have their own ground via the mounting screws...the ground interconnect between the two (probably the common of a DC voltage), supplies a potential ground loop. That's why when a clean PC supply was installed in one test, the hum went away...you no longer had the ground interconnect between power board and audio board.
I think THIS is definitely the problem. The solution though isn't exactly ideal... eliminating the path to ground through the common DC supply by adding a second power supply for the sound board.
Plus, disconnect the lamp matrix columns and rows from the driver board and see if anything changes. Could the strobing of the lamp matrix be generating the noise? I've listened carefully to various Data East games in attract mode and the noise seems to vary in volume depending on how many lamps are on. Plus, consider the fact that incandescent lamps draw more than 10 times more current than LEDs.
Do you have polarized/non polarized LEDs you can test with?
Quoted from ChadH:
So instead, I ordered a new Rottendog power supply.
Quoted from ChadH:
Hmmm... so now I am concerned. But those posts are from one year ago. I would think that those issues would have been resolved. Or should I still be concerned? Anyone know what exactly to check on the board to see if it has been improved?
Rottendog unfortunately isn't fixing the problems. Check your high voltage levels with a meter. I had a friend who installed a Rottendog power supply that caused fuses to blow and a burning smell. Even if your voltages are ok now the regulators will eventually fail since they are driven so much out of spec. I would recommend replacing the Rottendog with an X-Pin. Much better design.
Quoted from ChadH:
Dang. I checked and everyone is out of the X-Pin XP-DE5047 power supply.
So, the regulators on the Rottendog that are out of spec... wouldn't it be possible for me to swap those out with ones in spec? Has anyone offered up a solution? I'm good with a soldering iron but would just need to know what to do.
PinScores are virtually identical to X-Pin stuff, both brands are owned by Brett Davis. X-Pin just expands the selection of boards available and improves upon the already excellent design of the PinScore boards.
Wow whattya know!! Floating the sound board eliminated 100% of the noise! So even though floating the sound board doesn't work for some, it's the most sure fire way to solve this age-old problem.
Next I will have to verify the game is grounded. I want to get as much info on this specific machine (Jurassic Park) as possible. Any questions in particular you guys would like to ask about the boards etc. to increase the chances of success in the case doing this doesn't work for you?
Chad I was reading some of vid1900's posts in that Fire thread. He says if a component fails, shorts out, a cap dries up etc. that could change the intended path to ground, and the resulting difference in voltage/potential between boards would create a current in the ground line. But wouldn't this only be an issue on old (15+ year old) machines? I read some people talking about this also being a problem when the games were brand new in the early 90s, so evidently there was some other problem besides aging/failing components. We have previously established why we are seeing this issue (ground loops due to poor sound board design) but what exactly constitutes this "bad design" and why aren't all machines affected then?
Couldn't your theoretically install a diode on each board's ground connection to allow a connection to ground as well as preventing unwanted current from coming from the ground plane into said boards?
I made a very interesting discovery today... if your Data East/Sega jumbo DMD game has loud speaker noise (as in on par in volume with actual game sounds) check the part number of the sound board. I'm working on a Baywatch project that has a brand new X-Pin aftermarket power supply and perfectly working sound board that was recently repaired by Clive at Coin-Op Cauldron. The noise coming off that thing was terrible, and lifting the sound board's ground did absolutely nothing. The board was originally in a Sega Frankenstein, so on a whim we had the idea to swap them both back and see what happened.
THE NOISE WAS COMPLETELY GONE! With the sound board's ground lifted literally the only thing I heard was faint mains hum from the main transformer, and this was in a perfectly quiet room. So perhaps between games/sound board revisions the design has changed in such a way that ground loops can proliferate through the system if the board is installed in the wrong game. If you have a noise issue look up the board's part number in the manual for your game and see if it matches.
Now in my case, the Baywatch machine cleared up 100%. However, the Frankenstein machine the board was originally in (which was repaired with a few caps replaced in the process) did not clear up once we re-installed its board. Frankie also has an X-Pin power board. But that discovery alone I imagine could certainly help a lot of people banging their heads against the wall trying everything under the sun to get rid of the noise. Parts got swapped all the time when these games were on location. Give that one a shot and report back!