It looks like you may be missing a metal shield over the DMD. At least my game has one. That ground should attach to the metal stud on the lower left of that DMD.

There are definitely three different types of noise. Luckily I've never had an issue with the 60Hz noise from the main power but I have heard noise from both the DMD as the display changes and also noise from the playfield lamps as they change patterns in attract mode. My game (Rocky and Bullwinkle) has a little noise but it isn't too bad. I've heard much worse.

Lately I have had to repair quite a few Data East MPU boards (REV 3 and 4) and run them in my machine to test. While swapping around boards I've noticed when some MPU boards are running the noise is much worse and I've run across two that when installed the machine is quieter than normal. I have an extremely noisy board out of a Star Wars as well as another REV 3 board that is almost silent. I'm trying to compare the boards to see what the difference is but nothing has jumped out yet. I even pull off the inductors and tested those with a Sencore LC103 and the values were spot on with what the schematics say.

The schematics for the 5V section show a 470uf cap after the inductor besides the small .1uf one. That 18V lamp power doesn't have a similar cap to help smooth out the power for that so it may be worth adding one in parallel to C48. Maybe on the input side as well. It looks like the 18V lamp power is also used for the 12V regulator on the power board so a bit better filtering on that 18V supply may help.

I'd like to see if I can do something to the Star Wars board so it isn't as noisy. It would be nice to get it to a tolerable level without my friend having to install a separate power supply in his game to fix it.

Great input. You could be on to something. Exited to hear if you find a solution.

I know that is an option but I think it would be cool if at least some of the root causes can be identified. It looks like some of the noise may be from the MPU board. That hasn't been mentioned much. Most of the posts I've read are how to deal with it on the sound board or power board. Looking at the MPU may be worth exploring. If it ends up being a dead end at least we tried....

It would help to have more data about what game are silent with everything installed and tighten down normally (no floating sound boards) and what ones where inherently noisy.

If you have a Data East game could you please let me know a few details about it?

- Game noisy or not?
- MPU board revision -3 or -4, etc
- What brand and exact part numbers for the TIP42 and TIP122 in the lamp matrix
- What brand and exact part numbers for the TIP122 for the solenoid or replace parts
- If possible a picture of the MPU showing parts.

I want to see if there is any pattern with certain parts causing more noise that others.

Somewhere earlier in this thread I think vid1900 said the design may have worked fine in the lab when first built. That may be the case and during the run of the boards other brand of parts were used. Some of those may have different and undersirable characteristics. But when placed in a bar or location people just didn't care and it wasn't an issue.

I've seen some TIP transistors contain an extra internal diode and some not even though they carry the same part number. Could it be that something was used on some boards and causing an unexpected path to ground causing a ground loop? Maybe a poor cross that would normally be a non issue could be one of the thing making this thread unresolved for over 6 years.

So, just posting what TIP you have installed and if any were replaced will help. Some may be Motorola, others ST, and maybe other brands.

Robert

Any chance your have a scope? If so, take a look at the ripple on those lines. You can even check from ripple on the boards ground too (pick up the scope ground at perhaps the power supply, the check the ground at whatever board you are checking).

A little bit of a side issue, but I should probably mention - make sure wherever you add the 470uF, that the circuit supplying the voltage can handle the inrush current from the 470uF. Somewhat obscure, but better safe than sorry.

Floating grounds...I can relate to that. When 1st starting looking at mine, I bet there was only 2 ground screws per board.

After I found no significant power or ripple problems, I tried both floating the boards and thoroughly grounding them. Neither reduced the digital switching noise.

I think there is a parasitic effect happening, perhaps due to a error in design of trace proximity, analog/digital ground separation, package choice, or some other obscure design flaw.

I do have a scope and plan on pulling it out. I did watch the DVM on the 18V lamp supply and it was fluctuating a bit so it looks like there is some ripple on that line.

From what I can see on the schematics I don't see any issues with adding a 470uf cap but it is a good point to bring up. I'm going to get to see what the ripple looks like and if the cap helps or not.

There is one ground strap on the lower right side of the head that isn't connected in my Rocky and Bullwinkle. I posted the question in that forum topic to see if someone can get a picture of where those ground straps go so I can attach it to the proper place.

I have all the ground screws in the boards and they are tight. What I am seeing/hearing is that the issue shows up and varies by swapping out some different MPU boards (all other boards are untouched). So that leads me to believe that there is something going on with certain MPU boards that are generating some noise while others not. It seems to be one of the only unexplored areas in this whole thread. If it ends up being the source of noise then I think it would be good to resolve it at the source.

While the DE design of the power, MPU, and sound work I feel that some things are at the limits and right at the margins. If everything is perfect then it may be quite. If not then any of several different things could push it over the edge past where it should be and we get noise.

At the moment I am looking at the lamp matrix since that seems to make noise on some MPU's. I have theories as when the issue could be but it would help to get some data from other DE owners. If you aren't running the extra switching supply I (or of you are and had to) I really need to know what transistors are used in that matrix. Are they TIP42, TIP42C, TIP122, TIP 102, brand ST, Vortex, M Motorola, or something else? It would be interesting to see if there is any sort of pattern.

Maybe a certain brand or batch of parts were just off and although work may cause extra noise.

Anyone have a chance to peek in the backbox and see what is in there??

Thanks wayout (I actually thought robot was posting, I didn't read all the threads).

The ripple could actually be on the ground (either the backbox plate or the ground wires going to the boards, or both). Since the supplies are filtered...that's good and maybe gets rid of the ripple. But if the ripple is on the grounds, as far as the amp is concerned...it's still ripple. Hence, why many float the grounds. Grounds are tricky and I have to deal with them all the time (I design circuits that draw about 30A that are pulsed). A true 'ground' is almost really fictitious since most grounds actually have inductance and really isn't a 'true' ground. It might be fine for DC, but the ripple might not really see a good ground and the ripple just travels where there a path. So a person has to design such that either they try to isolate grounds (inductance in specific locations) or really provide a great ground (i.e. a good chuck of metal), or perhaps a 'single point ground' that forces all the grounds to what is considered ground. The single point ground is not used very often. Who knows what the plating on the backbox plates measures (impedance too) after all these decades.

It would be interesting if someone floated a board, then installed a series inductor on the all grounds going to the suspect board. Haven't looked how the external supplies have been hooked up.

Plenty of thick books written sole on grounding techniques. Sorry for being so long winded It really is an interesting subject.

I figure I'd add some simple graphics to my grounding comments above. Here's some very simple grounding examples that often creep up. Plenty of other scenarios, but I think a few pictures make a good enough point.

The top figure (1) shows two ground connections (A and B). Maybe A is from the MPU, maybe B is for the audio board. The ground symbol is what we will treat as the fictitious perfect ground. The inductors just duplicates the impedance of the ground connections. Could be from wire length, plating of the backbox metal, but whatever it is - it adds impedance to what we think is a perfect ground. So A and B really aren't at ground. Might be close, but not perfect This is actually OK since A and B ground connections are isolated since they are both forced to the perfect ground, and no current (ripple) can flow between A and B. We also are ignoring any coupling between wires, traces, etc.

Figure 2 shows maybe a wire from A connection to B, then going to the perfect ground. In this case some of the current on A can be imposed on B (bad). So now A can cause grief to B (or B to A).

Figure 3 is really bad. Let's say A and B are a great, low impedance connections to each other. But now you just have a lousy connection (inductance) to the perfect ground symbol. Any noise on A or B just zips right over to the other connection.

Lastly, keep in mind we aren't talking about the DC part, but rather the AC (i.e. ripple) part.

Sorry for the wordy electronics lesson. But it is really an interesting challenge chasing down grounding issues. As always: "The signal will take the path of less resistance." Might not even be an issue w/the DE noise, but since grounding was a topic, thought I would chime in. There's also the potential for radiated signals (i.e. something is acting like a transmitter, and something is acting like a receiver). The examples below are 'conductive', meaning the signals stay in the circuitry and not radiated. Switching supplies also cause a lot of grief too because of the switching currents.

There will be a test later.

pasted_image (resized).png

Keep in mind if there's ripple on the ground and the supply line where you measure, then it might not look like there's really any ripple. But maybe at the audio circuitry supply connections (i.e. at the IC, resistors, amp chip, etc.) - there could be ripple there between ground and B+. It's not really important (with in reason) what's at the board connector, it really the ripple at the audio circuitry that's important. Are you checking when the supply is loaded? Or unconnected?

Regarding the transistors - I wouldn't think that was the case, but at the same time I wouldn't rule that out. I guess maybe just not up near the top of my list. Usually when designing a transistor as a switch, you try to supply so much base current (or FET gate voltage), that even if the transistor had a crappy beta (or transconductance if a FET), that it would still act as a switch (i.e. it's always saturated really good). Don't know what's used in the matrix. My LAH is rather quiet, but sometimes it makes a slight noise but not enough to worry about. No external supply in mine. But my DE is not as nearly as quiet as my Williams or Bally.

I was checking the voltage with the game on and running. I was measuring at c48 and c49 right where the lamp power was coming in. As I saw the light patterns change I could hear it and see the voltage jumped around a little. I'll have to see what shows up on the scope.

Back to the MPU I'm trying to find out what could be different on games that are really noisey and those that aren't. That is why I'm looking at what parts were used. I have different brands on these boards but not enough data to go by yet. That is why I need others to chime in about what parts are in the board and loud or quiet.

I've noticed that some transistors of the same type test as they have an extra internal diode. Mainly on TIP102 devices but others could be effective too. If the circuit was designed with that in mind and it isn't there or if it wasn't planned and is now I'm circuit then that doesn't follow the original design.

If it's a TP102, that's a FET. There's inherently a parasitic diode due to the structure of the FET from drain to source. But it would always be reversed biased.

This guy:

pasted_image (resized).png

I agree with everything said about ground loops and how messy they are.

The matrix calls for tip122 but I've seen TIP102 devices dropped in as replacements. I still need to pull some of the data sheets for each of the parts. If I see enough of a pattern I'll pull all the tip devices out of the lamp matrix and swap the with another brand.

I've also seen similar pictures of tip122 darlington transistors. Some have that diode and some do not appear to have it. That is one of the things I want to see. Is the difference between these noisey boards and quiet ones due to a different brand tip122 that did or did not have that internal diode?

This doesn't mean there aren't ground loops or other sources of noise. Just trying to focus on this particular one.

Get one of these. Pretty darn amazing for $20. It measures and displays simple beta, not sure about tranconductance, but it does check FET's. Just not sure what it displays for info other than a FET is good. I can check if you want me too. Checks L's, C's and R's too. There's other flavors of it also. Makes for some very quick testing. You don't even have to worry about hooking up the wire to the correct pin - it sorts it out for you automatically.
pasted_image (resized).png

I have one of those testers too and worth every penny. That particular gadget is one that shows the diode on some tips while others do not. Not all tip122 devices seem to be created the same. While it may not mater in some circuits is this a contributing factor in the persistent DE noise?

I wouldn't think it would make a diff since it would be reversed biased and the FET should be on, so the FET would swamp it out. If it's leaky...then that's just a bad FET and maybe it would show up in the display acting weird when the FET should be off. There's not actually a separate diode per se in there, it's just part of the MOSFET structure die (see below). No expert by any means, but I don't recall seeing a MOSFET that doesn't have one, or if there is - I wouldn't say it's common. I should add I use mostly MOSFET's for switches.

That tester is pretty slick, isn't it?
pasted_image (resized).png

OK, I looked up a TP122. That's a darlington transistor. Generically speaking, you can sub a FET for the transistor as long as you have enough gate voltage to turn it on and it can handle the drain current (you probably know this, but I will toss it out anyways - transistors use current to turn on, FET's use a voltage to turn on). Darlington's have two transistors to increase the beta, MOSFET's - that's not an issue if the transconductance is high enough, just give it adequate Vg to turn on. Can't say I know anything about the TP122 diode (I'm assuming it's intrinsic?)
pasted_image (resized).png

I think we're getting off track a bit. Given that the DE design seems marginal and unless things are ideal it may not take much to push it over the edge and have it start making noise. With everything else the same I have different MPU boards (some same revision) that are quiet and noisey. So at least in this isolated case something on the MPU is generating noise. A good portion of the noise seems to be from the controlled lamps. Since the boards are all functioning I'm looking at part selection and different vendors for certain parts as the cause of the noise.

Ground loops are weird. They are just a PITA and it had been stated earlier in the thread that a part going bad may provide an easier path to ground causing a ground loop.

Am I seeing the switching noise because of different TIPs or some other component? I don't know yet but can try some things on the noisey board to see.

As soon as I start getting data in about other boards that will help to determine what parts to try swapping out first.

- Game noisy or not? (Jurassic Park)
Yes, some lamp matrix noise on audio that follows with inserts lighting. (zing..zing as inserts sweep)
Also, some constant buzz on audio, higher than 60hz. (150hz range?)
Neither audio noise is affected by volume setting high or low. (same even at zero volume)
Have tried floating sound board with no change.
The frequency of this noise makes it mainly come out of the right (smallest) speaker.

Also, DMD buzz/rings when displaying images, and is louder with more info displayed and minimal when DMD is blank. (buzz changes as info scrolls past)
It is separate from audio noise. If I unplug the sound board power, the DMD still buzzes. If I unplug the DMD, the DMD noise is gone, but the audio noise continues. (It may be partly because the DMD is mounted in a plastic panel, and not as sturdy as a wooden BW speaker panel)

- MPU board revision -3 or -4, etc (see photos)
- What brand and exact part numbers for the TIP42 and TIP122 in the lamp matrix
- What brand and exact part numbers for the TIP122 for the solenoid or replace parts
- If possible a picture of the MPU showing parts.

CPU PHOTOS-

1 (resized).jpg

2 (resized).jpg

LOWER RIGHT TIP42=TexasInstruments TIP122=Motorola 308

3 (resized).jpg

LOWER LEFT

TIP122=Motorola 306

4 (resized).jpg

5 (resized).jpg

UPPER RIGHT

TIP122 = Motorola 317

IMG_6984 (resized).jpg

Game: The Who's Tommy Pinball Wizard

I have (un)fortunately read every post in this thread. I have tightened, loosened, isolated all the boards. Have not put in a separate power supply.

When I read about that, I think is it the isolation that solves the issue(s) or is it the cleaner(more regulated) voltage??

Last night, I pulled my DMD/speaker panel out completely, I still have the attract mode noise. I never noticed the DMD hum also discussed in this column. When I pull the CN4 off the power supply this noise stops. Which makes sense as there is now no power for the light circuit. When I disconnect the lamp driver connector(CN7)(Lamp Columns) again no sound issues. Again makes sense because there is no power drop. Again, all noise is coming from the boards, not any speakers as they are disconnected. I do not remember if I disconnected CN6 (Lamp Rows).

Back to my initial question is it the isolation, grounding loops? or is it cleaner voltage? From all(nearly)500 posts, no one seems to have a consistent solution(other than power supply).

If it is dirty voltage, couldn't we replace the bridge rectifiers, to make sure they are not degraded, and add some inductor/ferrite bead/line filter between the F1 on the backbox and the bridge. This would help suppress the poor AC voltage quality, and therefore the new Bridges would be able to supply cleaner DC voltage?

If it is a grounding issue, could we not solder a grounding strap across the back of the CPU at the CN5 connector location(all pins) and tie that to the chassis?

I am an ME not an EE so I am asking questions.

If we used inductor what type would be recommended? What type of ferrite bead would you suggest? Any line filter would work correct?

Any input is appreciated as long as it is objective and helpful. You can keep your ME jokes to yourself

Can you send me a direct link for this. I am not seeing it on amazon!

There's a good reason you didn't see it on Amazon...it was Ebay!

There's a couple of flavors of transistor testers, so you should probably look around a little bit and find the one that best suits your needs.

ebay.com link: B1 Color 1 8 TFT ESR Transistor Resistor Diode Capacitor Mosfet Tester w hook

The power supply is by no means a guaranteed cure.

I have a Tommy with both the attrach mode/ lights noise and a persistent hum.

I tried everything suggested and then wired in a new power supply. No change I have given up on it now - spent waaaaaay too long on what ultimately is a minor issue, I crank up the volume and don't notice in game

There is more than one kind of noise problem, and different ways to solve each. It seems the design is insufficient in keeping analog audio and digital sections isolated and allowing ground loops or bleeding in noise ahead of the converters, and in some cases a separate supply mitigates the problem.

Well I just finished the above mentioned hack on my Rocky and Bullwinkle soundboard ground noise issue. Before installing the separate power supply I was getting a noise level of 62db just sitting there turned on. Now with the new power supply 41db. Well worth the hassle and 40 bucks. Now I can leave my machine on and not even think about it... Thanks to all the people that listed and showed the parts and directions to do this I very much appreciate it!!!

If you get a chance can you get some pictures of your main board? Also what kind of TIPs on the MPU

Our Baywatch machine was pretty noisy when idle. After replacing all capacitors on the power supply, the hum is virtually gone. You have to get really close to the speaker in a quiet room to hear the hum now. In this case, this is a power supply that came out of a Sega Sports redemption game and appeared to have the all orignal capacitors. The difference is astounding! Listen, this is with the mic very close to the speakers.

https://www.mediafire.com/file/9xhq8dw55lgaftg/noise.wav/file

Hey Guys,

Wanted to chime in here after reading all 10 pages of this thread! I recently picked up a Back to the Future Pin. When I first set it up at home, worked great, no buzz/hum. However, I literally moved it about 10 feet to the other wall in the room, plugged it in (to a different plug) and now I have the buzz/hum.

And yes, before anyone asks, I tried plugging in to the original outlet and the buzz/hum remains. I have tried several outlets, I have tried lifting the ground from the power plug, and I have tried floating the sound board. Floating the board actually made it worse...

I recently got a capacitor kit to replace the caps on the power driver board but haven't had a chance to install them. I will report back and let you know if that worked...

Jim

Well upon removing my power supply board and getting ready to de solder the contact, I found this!

Looks like a good sign to help solve the problem at least in my case! I’ll report back after the new caps are in!

20DF2860-BF50-4FB9-968E-6EC7C6CA306F (resized).jpeg

Well, I can confirm changing out the caps on the power supply board did NOT work lol.

It didn’t make it any worse, or better. Buzz / hum is exactly the same.

Guess I may try the sound board caps next...

I didn't read all 10 pages but has anyone had success with a new rottendog power supply improving the hum? In my case I don't want to install a switching power supply, I consider that a hack, but to each his own. The dmd makes it's own mild hum but doesn't improve the sound hum when unlpugged. If the lamps are contributing to the hum, I plan on switching to LED's anyway, wondering if that improves the hum. I may send my sound board out for a recapping just for the hell of it if nothing else works, will report back.

My Last Action Hero has a Rotten Dog PSU and has a very loud hum.

I actually did read through all 10 pages haha, and it seems like the Rottendog power board actually makes it worse for some people.

Has anything been done to your original power board? I'd make sure that is ok first. If it hasn't been touched it will probably at least need the capmfor the 5v replaced. Those often leak and I've had to replace many if them. I prefer the original boards.

An odd part in regards to hum sound is that I've seen it come and go depending on the MPU board installed. I've got a couple boards that are almost silent and one that is insanely loud. When I get more time I want to see if there are components on the MPU generating the hum and sending it to the sound card.

I thought the same thing...but switching EVERYTHING to LED's did not remove the hum. Didn't make it better, but also didn't make it worse, exactly the same. I recently replaced all the caps on the power supply board, but still the sam amount of hum remains. Next step is to replace the cap on the sound board, and will probably do that myself, just haven't gotten around to it...but from what I have read through this thread, that seems to work for some people.

Thanks for the input. I'm hoping the newest revised rottendog power supply will help more than hurt, needed one anyway. Then I'll swap out LED's, then I'll probably recap the sound board whether it needs it or not but I'm sure it won't hurt. BTW, not in this particular case, but I have had some improvements in the past by tightening the 4 bolts that bolt down the transformer, worth a try.

Been there, dont that lol. I tightened the bolts that go THROUGH the transformer to much that some of them ended up snapping and I had to replace them (and they are not a standard size/length so I had to order them online). But thats all good now, and did not help the hum.

Me, but I floated the sound board and it's tolerable now.

I was talking about the bolts that bolt it down to the bottom of the cabinet, not the bolts that go through the actual transformer. The idea being it helps to ground the transformer better to the ground strapping that runs underneath it, and I always seem to find those bolts are loose. It's not a miracle cure by any means but has improved the hum in a few instances.

Oh, yeah, I did those first...not luck, so then I tried the other ones.

I found the best solution starts around post 250 adding a second voltage converter. Cheap, easy and works 100%, my machine is dead silent now. It's a little ugly inside the back box if you a purist but easy to restore to factory condition.

Yeah, I saw that as well, though only going that route as a last resort.

Oddly I decided to try the ATX power supply method today and for whatever reason I cannot get the AXT psu to boot when it's plugged into the sound board. It will power up fine when it isn't plugged in though, so nothing is wrong with the jumper I have set to make it power up automatically.

you jumpered the green wire to ground (black)on the ATX PSU?

and you have connected ground, 12v, 5v and -12v to the soundboard?

The ATX PSU is known to work?

Yep to all of that. Even tested the PSU with a sata drive plugged in to make sure it spins up. Voltages also tested properly. I have an extra 850w Platinum (lmao) that I'm going to just test with tomorrow to try and figure out if it's just this PSU.

Maybe just a coincedence but
I have a DE JP
Once i cut the right speaker wires of the hum was gone.