(Topic ID: 280233)

Bottom cabinet speaker hum.

By 2manyhobbies

1 year ago


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Topic Stats

  • 23 posts
  • 4 Pinsiders participating
  • Latest reply 1 year ago by PinWoofer
  • Topic is favorited by 2 Pinsiders

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New Chip Installed (resized).jpg
Factory Speaker Replacement (resized).jpg
Practice Board (resized).jpg
Good U50 (resized).JPG
Bad U51 (resized).JPG
SB 2 (resized).JPG
SB 1 (resized).JPG
speaker-phase-diagram (resized).png
PXL_20201025_235141861 (resized).jpg
PXL_20201024_201752867 (resized).jpg
PXL_20201024_195551286 (resized).jpg

#1 1 year ago

Cabinet speaker hum?
Anyone ever run into this?
Don't seam to get any sound out of the speaker outside of a bad hum. I can unplug but the speakers up top really have a thin sound with out having this larger speaker working.
Have 13.5 VDC going to speaker. You think it is just a bad speaker? This is for #The Walking Dead Premium. #Stern S.A.M audio board.
PXL_20201024_195551286 (resized).jpgPXL_20201024_201752867 (resized).jpg

#2 1 year ago

You should not have a high DC offset like that. Your amplifier for that channel is failed, likely a DC blocking capacitor, but could be other causes too. Check speaker ohms also, with wires disconnected, it might also be damaged.

#3 1 year ago
Quoted from wayout440:

You should not have a high DC offset like that. Your amplifier for that channel is failed, likely a DC blocking capacitor, but could be other causes too. Check speaker ohms also, with wires disconnected, it might also be damaged.

Do you know what the normal voltage is going to the speaker?
I think the ohms reading of the speaker was 63 ohms but I can double check, do you know normal ohms for the speaker?
And the Blocking capacitor You were referring to I am assuming this is on the Power Driver PCB board And if so can you just replace cap or is it more the practice to replace the board?

#4 1 year ago

Normally the voltage going to the speaker is AC volts, not DC, and varies by the program material fed to it. The standard cabinet speakers in most games are 8 ohms. I'm not really familiar with the newer Stern games - but this is common for most solid state pinball. According to your diagram posted, the output amp circuitry is on the CPU/sound PCB. You'd really want to troubleshoot that circuitry and find out what component(s) have failed.

#5 1 year ago
Quoted from wayout440:

Normally the voltage going to the speaker is AC volts, not DC, and varies by the program material fed to it. The standard cabinet speakers in most games are 8 ohms. I'm not really familiar with the newer Stern games - but this is common for most solid state pinball. According to your diagram posted, the output amp circuitry is on the CPU/sound PCB. You'd really want to troubleshoot that circuitry and find out what component(s) have failed.

I couldn’t find a voltage chart for the speaker and since I was seeing a positive and negative symbol on the speaker I set me meter to measure DC voltage. I just checked it again with my meter set to AC voltage and I have 29VAC ( unless I reverse my meter leads at which point nothing) So polarity must be in play to get this voltage.

Is 29VAC About right you think?

#6 1 year ago
Quoted from 2manyhobbies:

I couldn’t find a voltage chart for the speaker and since I was seeing a positive and negative symbol on the speaker I set me meter to measure DC voltage. I just checked it again with my meter set to AC voltage and I have 29VAC ( unless I reverse my meter leads at which point nothing) So polarity must be in play to get this voltage.
Is 29VAC About right you think?

Also OHMs on the speaker was 10 ohms on low and 4 ohms on high. It is a upgraded speaker the previous owner put on. Was wired for the high setting, so 4 ohms. the manual that comes with the unit states factory speaker is 8” 4 ohm speaker
PXL_20201025_235141861 (resized).jpg

#7 1 year ago
Quoted from 2manyhobbies:

I couldn’t find a voltage chart for the speaker and since I was seeing a positive and negative symbol on the speaker I set me meter to measure DC voltage. I just checked it again with my meter set to AC voltage and I have 29VAC ( unless I reverse my meter leads at which point nothing) So polarity must be in play to get this voltage.
Is 29VAC About right you think?

Polarity only matters for phasing. The signal is still AC, and the positive mark is this side that gets the rising positive voltage to push the speaker cone outward, and a negative voltage to pull the cone inward. If the wires are reversed, you won't easily be able to tell that it is wired backwards. This factor really comes into play in stereo systems, where you want both speakers to be pushing out simultaneously with your program material.

Quoted from 2manyhobbies:

Also OHMs on the speaker was 10 ohms on low and 4 ohms on high. It is a upgraded speaker the previous owner put on. Was wired for the high setting, so 4 ohms. But the manual that comes with the unit states factory speaker is 8 ohms
[quoted image]

You can substitute 4 ohm for 8 ohm, but you would need to be careful not to use the amp at high volume because wattage will double if impedance is halved. Do I know for certain that using this aftermarket speaker in this game was a contributor? No, but it is possible - especially if you had the volume cranked up.

speaker-phase-diagram (resized).png

#8 1 year ago

Would you say that 29VAC going to the speaker is the problem. Meaning a board problem?

#9 1 year ago
Quoted from 2manyhobbies:

Would you say that 29VAC going to the speaker is the problem. Meaning a board problem?

Not necessarily, the voltage you read at the speaker terminals is dependent on the signal type and amplitude being sent to it.

#10 1 year ago
Quoted from 2manyhobbies:

Don't seam to get any sound out of the speaker outside of a bad hum.

Catching up - did you get this resolved or are you still debugging?

#11 1 year ago
Quoted from PinWoofer:

Catching up - did you get this resolved or are you still debugging?

Hey not resolved yet but I do have it diagnosed. I have dug into the manual and identified what voltages should be where and have done some voltage readings. The CPU sound board is suppose to have -12VDC and a +12VDC along with one +5VDC power coming in from the main power control, which I do have. The CPU sound board then sends the signal to the speakers, two channels one the two top speakers and one for the lower speaker giving me the issue.

Two top speakers work, and when testing for voltage going to those two speakers I get nothing, if there is a constant voltage supply then it most be a lower scale and something that is not of concern. However when testing for DC voltage to bottom speaker I have 13VDC constant and the speaker cone immediately pops out when you plug the wire into the speaker and when you unplug while live you can see a arc, which no speaker I have ever owned, for say a stereo, would do that and I am assuming neither should this.

So the CPU sound board is the culprit and like Wayout was saying probably a capacitor or something in the board. I did get a factory speaker before going through all the tests above for $16 in hopes of a simple repair just to try it out and of course same issue because I am never that lucky

I also, as a back up, ordered a couple of capacitors for the CPU sound board, they were less than a $1 from the place I ordered the speaker from, and was going to get a ESR meter which allows you to test capacitors while in circuit instead of unsoldering to test but after closer inspection of the board the solder joints are so small and the board looks so delicate that I am afraid to attempt.

Talked to two local repair shows, and when they run into problems with these newer boards they send out to Stern for rebuild attempts or possibly have to get a new board all together.

Sent a message to Stern support and they responded saying it does sound bad and to either purchase the board from a local distributor or have them send the board to them. Just messaged them back asking if I can send directly to them or purchase (not sure if they even rebuild) waiting on a response..

Hopefully they can repair the board, if not looks like the board would be $600, although Macro Specialties only seems to have this board for ACDC and Star Trek and I do not see it anywhere else when searching internet. So after this long story I am in a holding pattern and hopefully stern does not make me go through a middle man.

#12 1 year ago

I would try rob bodyguard at lockwhenlit.com and see if he can help as well.

#13 1 year ago
Quoted from pinballplusMN:

I would try rob bodyguard at lockwhenlit.com and see if he can help as well.

Does he specialize in rebuilding/fixing boards?

I am trying to get an answer from Stern if they can rebuild, they replied back a few minutes ago and said they will not allow me to send the board directly to them or purchase through them, still waiting to hear if they will likely repair my board or just say I need new

#14 1 year ago

2manyhobbies - there should be 0V DC (i.e. no DC offset) going to the speaker. You have measured ~13V so that's telling us that there is a short between the cabinet amplifier output and the 12V DC rail, and my money is on the amplifier chip U51 (TDA2030A) for the cabinet section. (I'm 99% sure this is the correct IC to address).

If you know how to solder you can order a new one and replace it yourself. Link below. If you know someone that can do the work better, have them do it.

If you do it yourself just be very careful; remove the heat sink, then clip the legs off of the chip leaving as long of a lead as possible. Heat the solder joint until the lead pulls out with little / no resistance with pliers. Remove the pins from each hole, clean up the holes and then replace the chip. There are small via (cyclinders) in the solder holes that can pull out and screw up the PC Board routing so be very careful. It is critical that you don't leave your iron on the joint for too long - excessive heat is bad. (Sorry if you already know all of this.)

This is what I would do and I think you have a 90%+ chance of this fixing the problem. This has happened to me before more than once.

Also, and maybe most importantly, you want to be 100% sure that the cabinet speaker was not the source of the board damage because if it is, you'll just end up blowing U51 again. Did this cabinet speaker ever work since you've owned the pin? It is unlikey that the speaker is bad but you might get a false negative of success if you don't proceed carefully after the board repair.

Hit me up if you want some help.

The ST Micro version of the TDA2030A is obsolete but Jameco still has a bunch of new old stock. At < $3 I recommend buying several for spares:

https://www.jameco.com/z/TDA2030AV-STMicroelectronics-TDA2030AV-18W-Hi-Fi-Amplifier-and-35W-Driver_1416796.html?%20CID=GOOG&gclid=CjwKCAjw8-78BRA0EiwAFUw8LGGl_NzHkMsSb5TsVpfdMsKSTN55CAVhz0OO_J-jGjDhO3pIRrOJwBoC3pEQAvD_BwE

SB 1 (resized).JPGSB 2 (resized).JPG

#15 1 year ago
Quoted from PinWoofer:

2manyhobbies - there should be 0V DC (i.e. no DC offset) going to the speaker. You have measured ~13V so that's telling us that there is a short between the cabinet amplifier output and the 12V DC rail, and my money is on the amplifier chip U51 (TDA2030A) for the cabinet section. (I'm 99% sure this is the correct IC to address).
If you know how to solder you can order a new one and replace it yourself. Link below. If you know someone that can do the work better, have them do it.
If you do it yourself just be very careful; remove the heat sink, then clip the legs off of the chip leaving as long of a lead as possible. Heat the solder joint until the lead pulls out with little / no resistance with pliers. Remove the pins from each hole, clean up the holes and then replace the chip. There are small via (cyclinders) in the solder holes that can pull out and screw up the PC Board routing so be very careful. It is critical that you don't leave your iron on the joint for too long - excessive heat is bad. (Sorry if you already know all of this.)
This is what I would do and I think you have a 90%+ chance of this fixing the problem. This has happened to me before more than once.
Also, and maybe most importantly, you want to be 100% sure that the cabinet speaker was not the source of the board damage because if it is, you'll just end up blowing U51 again. Did this cabinet speaker ever work since you've owned the pin? It is unlikey that the speaker is bad but you might get a false negative of success if you don't proceed carefully after the board repair.
Hit me up if you want some help.
The ST Micro version fo the TDA2030A is obsolete but Jameco still has a bunch of new old stock. At < $3 I recommend buying several for spares:
https://www.jameco.com/z/TDA2030AV-STMicroelectronics-TDA2030AV-18W-Hi-Fi-Amplifier-and-35W-Driver_1416796.html?%20CID=GOOG&gclid=CjwKCAjw8-78BRA0EiwAFUw8LGGl_NzHkMsSb5TsVpfdMsKSTN55CAVhz0OO_J-jGjDhO3pIRrOJwBoC3pEQAvD_BwE
[quoted image][quoted image]

Awesome and with out getting weird I love you man!!! LOL

How did you get such a clear pic of the inner works of the board? My manual on this section is not legible and the on line version was no improvement. And you are right it is that chip!!! Take a look at the pics, the good U50 and the bad U51 you just pointed out. The caps didn't look bad (which I know you can still have bad ones that look good) and didn't feel confident that was my problem and hated to de solder and check or try getting an ESR meter that I have never used before but I feel a lot better about this now

I have a factory speaker new that I only plugged in for a second to see if I would get lucky, I probably won't reinstall the Flipper fidelity speaker even though I still show it is good at 4ohms and no short to ground, plus I am wondering if the additional boost you get from the speaker may stress the system.

I am gonna order a few of the chips today and I will solder in, I will give you a update. Its been awhile since I have done this type of soldering so I will get one of the practice boards just to play first before do this.

Can't thank you enough!!

Bad U51 (resized).JPGGood U50 (resized).JPG

#16 1 year ago

Oh bye the way the cabinet speaker has been working, I have had this pin for a little over a year, I am 3rd owner and so far this is the only problem I have had with this pin. The guy I bought it from or the original purchaser upgraded this speaker, but the two up top in the back box were factory. Like I said I will just use the factory one.

Thanks again and I will post an update when I finish

#17 1 year ago
Quoted from 2manyhobbies:

you are right it is that chip!!!

The Stern SAM documentation (in my experience) shows a 4 Ohm cabinet speaker. So I don't see the speaker rating as the problem / root-cause here.

Like most things in electronics the impedance rating is not the complete story. The impedance rating is usually a nominal (average of lows) or DC reading. Meaning, if you use your multimeter to measure the DC impedance (resistance) you'll get 4 Ohm, 8 Ohm, etc. However, in reality the impedance changes depending on frequency.

Why does this mattter? Because the cabinet amplifier stage (U51) already has a low-pass filter. That large copper coil on the speaker serves to increase the impedance as the frequency of the audio increases. So, the coil also serves as sort of a doubled-up low pass filter. While this is redundant and otherwise does not cause a problem in the audio, it presents the amplifier with a higher impdance load as frequency increases. Class AB amplifiers are known to oscillate under high impedace loads (at well above the audible range) which taxes the final amplifier stage and results in excessive heating. Perhaps that's what blew out U51 since it was working before; time and temperature due to the load conditions.

Oscillations can be addresses in most cases by using a shunt capacitor to lessen the load value at progressively higher frequencies but it appears that C1 on the red speaker board is not populated. I don't know that this is what C1 was for (it looks like C1 was intended to be something else) but if it were me, I would not re-use that speaker. That's my opinion, others may vary.

#18 1 year ago

Now seeing the actual schematics, there is no DC blocking cap in the SAM system, so I am in agreement with the final output amp IC as being the likely culprit. I am wondering WHY it might have failed....was it briefly hooked up incorrectly, etc. Just thinking about how this might be repaired but fail again quickly in this scenario.

#19 1 year ago
Quoted from wayout440:

Just thinking about how this might be repaired but fail again quickly in this scenario.

Quoted from 2manyhobbies:

I probably won't reinstall the Flipper fidelity speaker

#20 1 year ago
Quoted from wayout440:

Now seeing the actual schematics, there is no DC blocking cap in the SAM system, so I am in agreement with the final output amp IC as being the likely culprit. I am wondering WHY it might have failed....was it briefly hooked up incorrectly, etc. Just thinking about how this might be repaired but fail again quickly in this scenario.

I think it could have been the speaker, not familiar with this upgrade but if a speaker is going to make it louder yet run off the factory circuit it has to stress that circuit. I always had kind of a thump sound when I would power this pin up but since unplugging this speaker it does not make that sound. I will be curious when I get the new parts if that sound will remain or if it will be like it is now with that speaker not hooked up. My other pin is silent as it powers up. I always thought that bump or thump when I powered it up was from a transformer but I am thinking it was not and just in the beginning stages of failure.

Should know by Monday when I get the part in. Thanks again for everyone’s help!

#21 1 year ago
Quoted from 2manyhobbies:

I think it could have been the speaker, not familiar with this upgrade but if a speaker is going to make it louder yet run off the factory circuit it has to stress that circuit. I always had kind of a thump sound when I would power this pin up but since unplugging this speaker it does not make that sound. I will be curious when I get the new parts I if that sound will remain or if it will be like it is now with that speaker not hooked up. My other pin is silent as it powers up. I always thought that bump or thump when I powered it up was from a transformer but I am thinking it was not and just in the beginning stages of failure.
Should know by Monday when I get the part in. Thanks again for everyone’s help!

The thump would probably be that DC offset pushing the speaker out. I assume a lot of folks have installed these aftermarket speakers in games without issue. Yours particular game could have failed for many reasons, it might have been the amp circuit in the game or a defect with the speaker, it could have been taxed by running too loud at some point, even by previous owner(s).

Just curious, for those altering the SAM system speakers, has anyone else noticed a power on thump that is more noticeable since your upgrade?

#22 1 year ago

Update. All fixed Thanks PinWoofer !! & way out

I bought a practice board to do some soldering first, since I have not done anything this small before: amazon.com link »

Was able to get a 10 pack of the amplifier chips for less then $10:amazon.com link »

Already had a soldering iron but here is the same one I used:amazon.com link »

Ordered a no clean solder wick to help remove solder from the holes so I can install the new chip: amazon.com link »

And now I am up and running. below are some of the final pics. I also notice a huge difference when I power this up now, no to very little noise using the factory speaker (like I said the upgraded one may have been going bad but use to make a very loud thump when I would first power on the pin...I didn't want to risk having the upgraded speaker cause my issue again)

If you are looking to upgrade a speaker use PinWoofer His systems are isolated and wont tax your factory control boards IMO

Factory Speaker Replacement (resized).jpgNew Chip Installed (resized).jpgPractice Board (resized).jpg

#23 1 year ago

Your repair skills are impressive - have fun!

- PinWoofer

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