(Topic ID: 184963)

Humming sound in old sterns


By rcbrown316

2 years ago



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  • 49 posts
  • 18 Pinsiders participating
  • Latest reply 1 year ago by Fytr
  • Topic is favorited by 10 Pinsiders

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#1 2 years ago

I have 3 old sterns with varying levels of the same problem. Big game, F2K and catacomb. All have humming sound when powered up. When you play the game you dont notice it that much but when idle I have to turn the volume down on catacomb and big game. All of them have been worked on multiple multiple times. Checked board grounds and cabinet ground braid. all seems ok there. Hoping someone has a good fix for this.

RB

#2 2 years ago

SED6 made a fix for humming for TSPP and I believe someone used it on LOTR. Might want to take a look at this thread and see if it could apply to your machines.

https://pinside.com/pinball/forum/topic/tspp-speaker-humbuzz-fixed#

#3 2 years ago

I don't have a lot of experience with old stern's. If it was a classic bally (which is very similar) I would suggest replacing capacitors, especially last filter capacitors. And maybe changing the pots on the soundboards.

#4 2 years ago

It's coming from the speakers rather than, say, something like the transformer? Try adjusting the volume pot, reseating sound board connectors and ribbon cables. Like Pmuis suggested, change the caps out on the sound boards. But that does sound unusual. I have 4 classic Sterns and none make any extraneous noise when on.

Quoted from Monk:

SED6 made a fix for humming for TSPP and I believe someone used it on LOTR. Might want to take a look at this thread and see if it could apply to your machines.

Unfortunately, completely wrong era of Stern.

#5 2 years ago
Quoted from schudel5:

It's coming from the speakers rather than, say, something like the transformer? Try adjusting the volume pot, reseating sound board connectors and ribbon cables. Like Pmuis suggested, change the caps out on the sound boards. But that does sound unusual. I have 4 classic Sterns and none make any extraneous noise when on.

Unfortunately, completely wrong era of Stern.

definitely coming from speakers I moved the transformer wires around just in case it was some type of interference. no dice. I will try the caps. I have hundreds of them and have rebuilt the bally stuff before.

#6 2 years ago
Quoted from rcbrown316:

definitely coming from speakers I moved the transformer wires around just in case it was some type of interference. no dice. I will try the caps. I have hundreds of them and have rebuilt the bally stuff before.

Just for shits 'n giggles, try swapping around the sound boards between games and see if it gets better, worse or stays the same.

#7 2 years ago

there are some largish electrolytic caps on the sb300 sound board that take a moment to charge up. You get some nice hum when you flip the power switch as they charge up. If you power cycle twice rapidly, you will probably not hear it as the caps held some charge.

Perhaps recap the sound board. Some of the power on hum is unavoidable (i think this is what you are describing).

#8 2 years ago

My Galaxy has a loud hum,comes from that giant transformer,I'm told!!!

#9 2 years ago

My Hot Hand did this too. Assumed it was the caps but didn't get around to replacing them before I sold it.

#10 2 years ago

I've been told they hum because they don't know the words.

#11 2 years ago
Quoted from zacaj:

My Hot Hand did this too

Thanks for my first down vote. I'm sincerely sorry for ruining your day.

#12 2 years ago
Quoted from Monk:

Thanks for my first down vote. I'm sincerely sorry for ruining your day.

I up-voted you because you were only trying to help.

#13 2 years ago
Quoted from schudel5:

I up-voted you because you were only trying to help.

Thank you for clarifying that I was in the wrong era and the up vote. My first down vote was bound to happen at some point. Figured it would have happened a lot later at night and involved a lot more alcohol.

#14 2 years ago
Quoted from Monk:

Thanks for my first down vote. I'm sincerely sorry for ruining your day.

Woah dude. If it means that much to ya I'll undo it....

I'm just very tired of people with negative reading comprehension

#15 2 years ago
Quoted from zacaj:

Woah dude. If it means that much to ya I'll undo it....
I'm just very tired of people with negative reading comprehension

No worries it's just votes, keep it there. I was just trying to help the person asking a question. I am not an expert by any means (more like a complete amateur) I was just trying to pass along some information that I stated may or may not work. Sorry for completely derailing the thread. Now that deserves a down vote.

#16 2 years ago

My Meteor hums as well - it's at a friends house now so haven't had a chance to look into it. I would suspect old dried out electrolytic caps on the sound board.

#17 2 years ago

The ground for the sound board goes through the connectors. Repin those with some new trifurcon pins.
J2 - pin 3,2,8 all point to ground.

Also, check your volume potentiometer in the bottom of the cabinet. I haven't had to replace one of these yet; usually working the knob back and forth clears up static.

And, as others have said; get a cap kit and replace them all.

#18 2 years ago
Quoted from brenna98:

The ground for the sound board goes through the connectors. Repin those with some new trifurcon pins.

Don't those soundcards use all .100 Molex connectors? They don't make Tiburon connectors in .100, just the .156 size.

#19 2 years ago

connectors on catacomb have been replaced. I ought to double check the job they did. I have cleaned the volume pots on all the games. they were static"Y" but no more. hum is still there.

#20 2 years ago

I bought a Stern Ali last year, and the first thing I noticed was the humming on power up. I have a lot of spare parts around, so I used some wires with alligator clips and jumpered a 5,000 uF 50Vdc capacitor in parallel with existing capacitors on the sound board and found the problem pretty quickly.

Looking closely at the boards in the head, I notice that all those filter capacitors are very old. I'm surprised any are still working.

When I get a chance I will replace them all with news ones. I have a bigger fix to perform first though, the last owner butchered the connectors to the AS 2518-18 rectifier/fuse board and soldered some wires directly to the board and it looks pretty sketchy.

For sure though, your humming will be traced to one or more bad capacitors.

#21 2 years ago

My Flight 2000 hums, not loudly but noticeable for sure. I replaced all the caps on the sound board, and it made no difference.

#22 2 years ago

If it is not coming from the speakers it could be the coil in the coin lock out mech ,in the coindoor .

#23 2 years ago
Quoted from trilogybeer:

If it is not coming from the speakers it could be the coil in the coin lock out mech ,in the coindoor .

yep seen that before...but thats not it.

#24 2 years ago

For what it is worth, my Star Gazer has the same issue. Constant background hum just slightly louder than I'd like to live with.

I also replaced the main large caps on the sound board and it made no difference (as well as on the solenoid driver board).

I'll try the re-pinning the ground connectors when I get a chance. What is the coin door lockout solenoid issue?

#25 2 years ago

ground loop? The MPU j5 to sb300's similar plug is connected together. Then there is also the larger .156 plugs down for the 12v in, analogue out etc. Perhaps the SB300 .156" connector pins are cracked / high resistance and the the ground return goes back through the 34 pin connector creating noise?

In general my WMS 3-7 games have a lot more hum than my Stern MPU200 games.

3 weeks later
#26 2 years ago

Okay, so you've got 3 MPU-200 games that all use the same SB-300, with the exception of Flight 2000, which has the speech board as well.

Let's start with the SB-300 tests, then.

For each game, measure the following, setting your meter for both DC, and then AC volts, respectively:

- Measure voltage (DC, then AC) between TP6 on the SB-300 and ground on the MPU.
- Measure voltage (DC, then AC) between TP6 on the SB-300 and ground on the chassis somewhere (the braid is fine.)

- Now, disconnect J3, and measure DC and AC volts from pin 8 of J3 to ground on the MPU, and the chassis somewhere.

We're checking the differential between different bonding points on the SB-300 and other components. Ground pins and
braid might look okay, but since poor bonding leads to a lot of these problems, it's worth the check with the meter.

Then, if you have a clip lead, clip the black lead from your meter to TP1 on the SB-300, and you can leave it there
while you take the next set:

- Measure DC & AC volts at TP3 (+12V)
- Measure DC & AC volts at TP2 (+10V)

- Measure DC & AC volts at TP4 (+5V)

Report back for each game (or even all three at once, if they're handy, and we can talk about next steps.)

#27 2 years ago
Quoted from Majdi:

Okay, so you've got 3 MPU-200 games that all use the same SB-300, with the exception of Flight 2000, which has the speech board as well.
Let's start with the SB-300 tests, then.
For each game, measure the following, setting your meter for both DC, and then AC volts, respectively:
- Measure voltage (DC, then AC) between TP6 on the SB-300 and ground on the MPU.
- Measure voltage (DC, then AC) between TP6 on the SB-300 and ground on the chassis somewhere (the braid is fine.)
- Now, disconnect J3, and measure DC and AC volts from pin 8 of J3 to ground on the MPU, and the chassis somewhere.
We're checking the differential between different bonding points on the SB-300 and other components. Ground pins and
braid might look okay, but since poor bonding leads to a lot of these problems, it's worth the check with the meter.
Then, if you have a clip lead, clip the black lead from your meter to TP1 on the SB-300, and you can leave it there
while you take the next set:
- Measure DC & AC volts at TP3 (+12V)
- Measure DC & AC volts at TP2 (+10V)
- Measure DC & AC volts at TP4 (+5V)
Report back for each game (or even all three at once, if they're handy, and we can talk about next steps.)

thank you so much for this direction. I will get to this in a few days hopefully.

#28 2 years ago
Quoted from rcbrown316:

thank you so much for this direction. I will get to this in a few days hopefully.

Ditto, been crazy busy but will be looking at this soon.

#29 2 years ago

Here are my readings from Star Gazer:
All mpu ground connections were via TP3/grd on my Alltek mpu board.

- TP6 on the SB-300 and ground on the MPU: 0.08vdc. 0.003 vac

- TP6 on the SB-300 and ground on the chassis somewhere (the braid is fine.): 0.085vdc. 0.024vac
- Now, disconnect J3, and measure DC and AC volts from pin 8 of J3 to ground on the MPU, and the chassis somewhere: 0.1vdc. 0.3vac cab braid, -0.009vdc 0.004vac mpu ground

... clip the black lead from your meter to TP1 on the SB-300, and you can leave it there
while you take the next set:
- Measure DC & AC volts at TP3 (+12V): 9.99vdc. 0.003vac

- Measure DC & AC volts at TP2 (+10V): 14.67vdc 0.07vac
- Measure DC & AC volts at TP4 (+5V): 4.89 vdc. 0.006 vac

What do these indicate?

1 week later
#30 2 years ago

Sorry for the delay: rough work travel week.

I assume you swapped TP2 and 3 around in that post.

In which case: TP2 seems a bit high. It's listed on the SB-300 schematic as 11.9VDC.

Can you check at TP3 on your power driver board as well?

And do you know if the power transformer is set for high or low line voltage (is the line
input to the transformer between pins 1 and 9 or 1 and 5?

#31 1 year ago
Quoted from Majdi:

Sorry for the delay: rough work travel week.
I assume you swapped TP2 and 3 around in that post.
In which case: TP2 seems a bit high. It's listed on the SB-300 schematic as 11.9VDC.
Can you check at TP3 on your power driver board as well?
And do you know if the power transformer is set for high or low line voltage (is the line
input to the transformer between pins 1 and 9 or 1 and 5?

My reading for TP2 is correct, but you're right that it is the 12v testpoint, not the 10v one.

On the SDB TP3 I read 14.85vdc, board writing says it should be 13VDC.

My transformer is set to 115v, yellow wire to lug 9.
IMG_1315 (resized).JPGIMG_1314 (resized).JPG

2 weeks later
#32 1 year ago

Do you actually need it at 115V? That might cause unregulated supplies to float up a bit higher than expected.

What's the line voltage coming into the machine? (Obviously, be careful checking this one

#33 1 year ago
Quoted from Majdi:

Do you actually need it at 115V? That might cause unregulated supplies to float up a bit higher than expected.
What's the line voltage coming into the machine? (Obviously, be careful checking this one

That's just how it was setup when I got it and I've never given it any thought until now.

AC at the plug reads 128v.

I guess I should try switching the transformer over to 120v.

#34 1 year ago

It doesn't surprise me. 99% of the pins I've looked at are set for 115V. Most don't need to be these days (my own line voltage at home is consistently 121-122V.)

Your 128V line voltage and 115 tapped winding probably explain the 15V where it says 13.

If nothing else bringing down the unregulated lines will take some heat out of the backbox (linear regulators used to derive the regulated busses from them have to dissipate the excess as heat, so switching to the 120V tap should cool things down a bit.)

Might also be worth seeing if your hum improves after. Less stress all around is never bad.

#35 1 year ago
Quoted from Majdi:

It doesn't surprise me. 99% of the pins I've looked at are set for 115V. Most don't need to be these days (my own line voltage at home is consistently 121-122V.)
Your 128V line voltage and 115 tapped winding probably explain the 15V where it says 13.
If nothing else bringing down the unregulated lines will take some heat out of the backbox (linear regulators used to derive the regulated busses from them have to dissipate the excess as heat, so switching to the 120V tap should cool things down a bit.)
Might also be worth seeing if your hum improves after. Less stress all around is never bad.

Yeah it's easy enough to do, worth trying for sure. I'll report back once I have a chance to switch it over to 120v.

#36 1 year ago

Okay, switched it over to 120V at the transformer. No noticeable change in the background hum level, unfortunately.

I redid the level tests on the sound board as before, only changes were:
- Measure DC & AC volts at TP2 (+12V/13V): Was 14.67vdc now 14.03vdc
- Measure DC & AC volts at TP4 (+5V): Was 4.89 vdc Now 4.84vdc

So very slight drop in those two values.

I also thought the noise might be caused by a new switching-type 5v power adapter I used on my power board, so tried the game with the power board out of my Flash Gordon with the analog style adapter, no change in the background hum.

Finally, I noticed that the hum only starts once the MPU board has booted up. When in attract mode, the sound kind of changes with the light pattern. I tried running the game with everything unplugged from the MPU board except J4, so no actual controlled lamps are switching, etc, same background hum. Note that my game is using an Alltek MPU board as well.

At this point I'm wondering if a high-pass filter/cap at the right spot might cut most of the noise, hopefully while preserving the normal range of game sounds and quality? Ironically, my Medusa which seems a bit muffled now has virtually no detectable background hum.

#37 1 year ago

The unregulated drop to 14 V is heartening. With proper regulation the 5V bus won't change much, no, so that looks fine.

The MPU controls the audio chain, including muting, so it doesn't surprise me that you don't hear anything until it boots. The hum coupled to the light pattern is interesting, and means it might be coming from the MPU itself.

That's the good news.. bad news: I haven't seen a schematic for the Allteks (which I'll need to start going down that path.) Have you tried asking them about hum issues in Sterns? It might be worth seeing what they say.

Do you have a Stern MPU and ROMs? Might be worth a quick A/B test.

#38 1 year ago

I'm working on getting the original Star Gazer MPU board working again (https://pinside.com/pinball/forum/topic/help-me-fix-this-stern-mpu-200-board).
Once I achieve that, it will replace the Alltek board, which actually belongs in my Flash Gordon.

So at some point in hopefully the not too distant future I can try that.

#39 1 year ago
Quoted from Fytr:

Okay, switched it over to 120V at the transformer. No noticeable change in the background hum level, unfortunately.
I redid the level tests on the sound board as before, only changes were:
- Measure DC & AC volts at TP2 (+12V/13V): Was 14.67vdc now 14.03vdc
- Measure DC & AC volts at TP4 (+5V): Was 4.89 vdc Now 4.84vdc
So very slight drop in those two values.
I also thought the noise might be caused by a new switching-type 5v power adapter I used on my power board, so tried the game with the power board out of my Flash Gordon with the analog style adapter, no change in the background hum.
Finally, I noticed that the hum only starts once the MPU board has booted up. When in attract mode, the sound kind of changes with the light pattern. I tried running the game with everything unplugged from the MPU board except J4, so no actual controlled lamps are switching, etc, same background hum. Note that my game is using an Alltek MPU board as well.
At this point I'm wondering if a high-pass filter/cap at the right spot might cut most of the noise, hopefully while preserving the normal range of game sounds and quality? Ironically, my Medusa which seems a bit muffled now has virtually no detectable background hum.

this description is exactly whats happening on all 3 of my games. all have alltek ldb's

#40 1 year ago
Quoted from Fytr:

I'm working on getting the original Star Gazer MPU board working again (https://pinside.com/pinball/forum/topic/help-me-fix-this-stern-mpu-200-board).
Once I achieve that, it will replace the Alltek board, which actually belongs in my Flash Gordon.
So at some point in hopefully the not too distant future I can try that.

Been a while since you've posted in that thread...how's the MPU project going?

2 months later
#41 1 year ago

Built my first SB-300 replacement board and have been messing with it all day. Found that the 60cycle hum can be a bit tedious to get rid of. I thought my analogue grounding at the bottom of the board would be plenty sufficient but its not on the first proto. Running a wire to the ground of C7 and C8 and soldering it right to the analogue ground the header pins (j2-p2&3)clears up a hit of hum. Soldering a wire from the ground connection of the tda2003 amp right the analogue ground header pin cleaned up the rest of the hum. I am going to have to go back and fix the analogue ground pour at the bottom of the PCB.

Another note. If the V10 circuit is out of spec (low) the sound will be too loud and you get what i think is wave clipping on higher tone notes (power on tones sound like crap). I did not have a 10v zener on hand yet, so i used two combined two zeners to make a single 9.8v zener. That 0.2v was enough to cause a substantial sound quality problem. I stole a 10v zener off another board (it was goin 10.2v) and it made the sound volume go down and be much better sounding. So good to take a peak at the V10 circuit (TP3). Failing electro caps will drag the voltage down too. V10 is used for the MC3340 circuit.

#42 1 year ago

I'm gonna just leave this here and back away...a low-tech solution??

https://pinside.com/pinball/forum/topic/noisy-humming-transformer#post-2222061

faz

#43 1 year ago
Quoted from barakandl:

Built my first SB-300 replacement board and have been messing with it all day. Found that the 60cycle hum can be a bit tedious to get rid of. I thought my analogue grounding at the bottom of the board would be plenty sufficient but its not on the first proto. Running a wire to the ground of C7 and C8 and soldering it right to the analogue ground the header pins (j2-p2&3)clears up a hit of hum. Soldering a wire from the ground connection of the tda2003 amp right the analogue ground header pin cleaned up the rest of the hum. I am going to have to go back and fix the analogue ground pour at the bottom of the PCB.
Another note. If the V10 circuit is out of spec (low) the sound will be too loud and you get what i think is wave clipping on higher tone notes (power on tones sound like crap). I did not have a 10v zener on hand yet, so i used two combined two zeners to make a single 9.8v zener. That 0.2v was enough to cause a substantial sound quality problem. I stole a 10v zener off another board (it was goin 10.2v) and it made the sound volume go down and be much better sounding. So good to take a peak at the V10 circuit (TP3). Failing electro caps will drag the voltage down too. V10 is used for the MC3340 circuit.

Pretending that I understood most of what you are saying, would any of this likely be applicable to the Alltek board as well?

#44 1 year ago
Quoted from Fytr:

Pretending that I understood most of what you are saying, would any of this likely be applicable to the Alltek board as well?

The Alltek or any replacement mpu would not fix analogue humming on the sb300 sound board.

To test ground problems. Put a gator clip on the amplifier tab and touch the ground braid. If it fixes the hum, you have connector / ground problems.

#45 1 year ago

buzzzzzz

Have something to try that may help games with buzzing sound boards. I noticed the ground (and +12v) connector pin are double wire crimped together. One wire goes the SDU for ground return, the other back to transformer for return (same with +12v). There is two PCB headers for the ground connection (and +12v) so lets tie those all together for a strong connection.

original connector setup with two wires in one crimp
SB-300 J2 connector pin out

Take the two ground wires and separate them apart. Use a DMM to check for almost no resistance between each ground wire and the earth ground(should be same nearly same resistance as shorting your DMM leads together).

checking analogue ground returns

Use two new crimp contacts and put one wire at p2, the other at p3. A couple inches back, cut both ground wires apart. Use a wire nut or neatly solder and heat shrink tube all four wires together. You can do the same for the +12v connection. Install new headers at J2.

wires still twisted together but the connector contacts have been doubled

The transformer and SDU J3 connectors must be good. SB-300 1000uF and 470uF cap must be good as well as the sb-300 V10 circuit needs to be bang on 10v.

#46 1 year ago
Quoted from barakandl:

buzzzzzz
Have something to try that may help games with buzzing sound boards. I noticed the ground (and +12v) connector pin are double wire crimped together. One wire goes the SDU for ground return, the other back to transformer for return (same with +12v). There is two PCB headers for the ground connection (and +12v) so lets tie those all together for a strong connection.

So is this just taking care of possibility of badly crimped double wires? Assuming the old board and your new board have those pins tied together via traces like in the schematic, electrically I'm not seeing a difference in what you're doing here.. but maybe I'm missing something.

#47 1 year ago
Quoted from acebathound:

So is this just taking care of possibility of badly crimped double wires? Assuming the old board and your new board have those pins tied together via traces like in the schematic, electrically I'm not seeing a difference in what you're doing here.. but maybe I'm missing something.

I noticed some games would clean up a bit of hum by taking an aligator clip from the tab of the amp to the backbox ground braid. After doing the mod above it also fixed up the hum.

Decent amount of current seems to go through the analogue ground. When there is resistance in the connector the amplifier is at a different ground potential makes the sound board have a pretty nasty 60 cycle hum. There is no backbox ground mount on the SB-300, it all goes back through that J2 P2&3. It also is kinda odd one return to SDU and one to rectifier. Making sure there is a low resistance connection to ground helps keeps the noise out. Since the PCB has two header ground posts, I think it was probably intended to be done like I did except it was easier to manufacture the double wire in a single crimp.

#48 1 year ago
Quoted from barakandl:

buzzzzzz
Have something to try that may help games with buzzing sound boards. I noticed the ground (and +12v) connector pin are double wire crimped together. One wire goes the SDU for ground return, the other back to transformer for return (same with +12v). There is two PCB headers for the ground connection (and +12v) so lets tie those all together for a strong connection.

Take the two ground wires and separate them apart. Use a DMM to check for almost no resistance between each ground wire and the earth ground(should be same nearly same resistance as shorting your DMM leads together).

Use two new crimp contacts and put one wire at p2, the other at p3. A couple inches back, cut both ground wires apart. Use a wire nut or neatly solder and heat shrink tube all four wires together. You can do the same for the +12v connection. Install new headers at J2.

The transformer and SDU J3 connectors must be good. SB-300 1000uF and 470uF cap must be good as well as the sb-300 V10 circuit needs to be bang on 10v.

Interesting. I'll give this a try on my Star Gazer when I get a chance. Thanks!

3 months later
#49 1 year ago

I never got a chance to try barakandl suggestions above, but I did replace the Alltek MPU with the original Star Gazer MPU-200 board that I finally got working again (battery damage) and the loud background hum is gone.

Something about the Alltek board I guess. Maybe because it only used that one grounding screw on the bottom left corner...

Strangely, I moved that same Alltek board into a recently acquired Big Game while I fix its MPU board (battery damage, always battery damage) and I don’t have the same hum as I did with Star Gazer. Big Game has leds in the backglass and GI, Star Gazer doesn’t, I wonder if that is a factor?

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