(Topic ID: 144797)

WPC Sound Board problem

By Edster

8 years ago


Topic Heartbeat

Topic Stats

  • 26 posts
  • 11 Pinsiders participating
  • Latest reply 7 years ago by rksnapper
  • Topic is favorited by 1 Pinsider

You

Linked Games

#1 8 years ago

Need help. I have an issue with my sound board on my MM. The connector to the cabinet speaker (J504) pin #1 and #2 are both showing 14v. I checked another game and they are not anywhere near this. I replaced the diodes right above the connector, but that was not the issue.

When connected, the speaker is starting to hum and I can smell it burning. Obvious due to the voltage. This happened suddenly while playing. Something had to blow.

Anyone have any suggestions where I can start to look?

Thanks.

#2 8 years ago

Check the voltage regulator transistors and tantalum caps in line with them would be the first place I would check.
Good luck.

#3 8 years ago

Yep, PSU is a good place to start. My guess would be the amplifier IC though, I've seen one do a similar thing before, though by the time I saw it the whole amplifier IC had exploded, so not too hard to diagnose.

#4 8 years ago

Thank you for your suggestions. I try them and post my results.
When I power it up with the speaker connected I get a loud hum and the speaker is vibrating like crazy, most likely due to the huge current going to it.

#5 8 years ago

You can power on for short periods without speakers connected. But amps like to be driving a load.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info

#6 8 years ago

So is there 2 amps? 1 for the backbox speakers and one for the cabinet woofer?
I am getting sound on the backbox so I assume yes.

How do I test an amp?

#7 8 years ago

Yes, two separate amps, pair of TDA2030s. Wouldn't be a bad idea to grab the WPC95 schematics and have a look at how they're configured. There are several ways to check amps. A good start is checking the power rails, but if one amp is running OK, chances are that isn't the problem (they share a power supply). If I wanted to be careful, I'd probably disconnect the input to the bad amp, and see if the hum/DC output goes away, but really, given the type/config of this amp, I doubt the problem has anything directly to do with the input. For a start it has a decoupling cap on the input (C38, C39), so a DC input would just cause a thump, not a constant DC output. Not too sure what else to suggest; if I had that board here I'd check signals at its pins, and just replace the amp IC if they looked sane apart from the output.

#8 8 years ago

I think the hum is coming from the excessive power to the speaker. It is making the speaker vibrate erratically. I see that 12v is going to the speaker. Checking the voltage on another board, no where near that.

#9 8 years ago

Saving for future

3 weeks later
#10 8 years ago

So I have a guy that is able to repair my board but cannot do it until the New Year. No problem, so I swapped out the sound board form my SS and used it instead. Sound was working fine for the past month and low and behold, today the same thing happened. My son was playing an very good long game of MM and then the cabinet speaker cut out. Same issue as before. So now I am down 2 sound boards.

Is it possible this is a coincidence or is there something else that could be blowing the amp IC? I hate to repair these boards and have another one blow again. Argh.

Everything on the sound board is fine. The cabinet speaker works when plugged into the backboard. There is a hum now when the game is turned on. Exactly like before on the other board. Most likely I am getting a larger voltage out to the speaker like before.

It's just strange to have this happen again and again during a long play. Maybe it's overheating and blowing the IC? I'm paranoid now and a little depressed

#11 8 years ago

You need to investigate your voltage source (PSU). This isn't paranoia. This flat out won't happen on two different machines, built to drive identical speakers. No coincidence.

#12 8 years ago
Quoted from Edster:

the speaker is starting to hum and I can smell it burning

Possible the speaker-coil has lost insulation and is now on very low resistance. Check that too.

#13 8 years ago

Have you measured the resistance of the speakers?
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#14 8 years ago

resistance of the speakers... I never thought of that. I will try today. Thanks.

#15 8 years ago
Quoted from Edster:

resistance of the speakers... I never thought of that. I will try today. Thanks.

Yeah, if the coil melted, which sounds like what happened, all kind of neat things can happen that can screw up an amplifier. I've had a lot of fun repairing guitar amps of all types due to this. Essentially, the speaker starts to need more power, which draws too hard on the amp and kills it. Very common in lower wattage amp set ups, especially solid state.

#16 8 years ago

Seems the resistance on my working game is ~4.9 and this one is ~3.9 doesn't seem like that is a huge difference. Once I get both boards repaired I am going to be scared to use it in this game.

It took a month or so for it to blow. Again only during a long game 20-30 min.

1 week later
#17 8 years ago

I got the same thing going now with one of my boards that came out of a Safecracker. My situation started out a bit different though. My Safecracker after just sitting on for a few hours would produce a very load buzzing noise simular to a dryer completion signal or alarm for just a moment and stop. Finally it started doing the same thing you describe and it trashed my back box speaker. (Constant buzz and burning smell) I bought a sound board repair kit from Marco (both amps, both op amps, both caps,) installed it no change. So I'm scratching my head with a schematic.

#18 8 years ago
Quoted from Edster:

~4.9 and this one is ~3.9 doesn't seem like that is a huge difference.

I would call a decrease of >20% quite substantial. And it is possible more since Dig.MultiMeter are not accurate in this low range.
Together with the burn smell, it would be a good reason to replace the loudspeaker.

#19 8 years ago

Interesting. You are probably right as I cannot figure out what else could cause this. I have a the pro audio speaker upgrade. There is a coil that came with it, I guess that is the enemy right now. I think I might just install the old speaker.

#20 8 years ago
Quoted from Edster:

Interesting. You are probably right as I cannot figure out what else could cause this. I have a the pro audio speaker upgrade. There is a coil that came with it, I guess that is the enemy right now. I think I might just install the old speaker.

That's a good piece of info that the speaker is not stock. What do you mean by the coil that came with it and what is the wattage/ohm rating of this replacement speaker?

#21 8 years ago

There is a could that the speaker plugs into that goes to the Sound board. I thought it came with the speaker but I may be mistake as it's been so many years. I post a photo of the speaker later today.

2 months later
#22 8 years ago

Just wanted to post an update. I sent out both boards for repair and they both had the amp blown. I pulled my cab speaker and replaced it with another one. The one in was a Pro Pinball Sub. Now I am using a stock speaker. All is well. Played tons of games on both machines and so far no issues.

Not depressed anymore and thanks to all that responded to this thread

2 weeks later
#23 7 years ago

All,
I have a similar problem and wonder if the same think happened. I have a TOTAN with a FF speaker upgrade. When adjusting the volume, it seems like I have to have it set at an unusually high level to get the same sound I get on other machines (like mid teens to get the same sound 8-9 gives on others). Well, after playing about a dozen games with the sound cranked up to about 22 to get those nice subwoofer sound effects, I simply lost the cabinet speaker sound and back box speakers remained. I checked the sub and heard the same 60hz buzzing sound mentioned above and the heatsink on the amp was so hot you couldn't touch it for more than a second. Figured it was overdriven and let it cool down. Nope...as soon as the game is switched on, I immediately get the hum before the game finishes booting.

Sounds like I blew the same amp as above. My question is: why would FF give you an upgrade that kills the original amps? I went to their website and didn't see anything that says "don't crank the sound" too loud. Is there anything I can do to eliminate this problem after I replace the amps with a SB repair kit? Increase the resistance to the sub(maybe turn it down if it has its own rheostat? Lastly, if the amp blew, why would the amp heat sink still get HOT? Thank you!

#24 7 years ago

I wonder if the FF speakers are the right impedance?

The hum may very well be a shorted amp. It'll hum and get hot.

#25 7 years ago

Are you guys using spade connectors to hook up the speakers or soldering wires right onto the leads? If you have exposed leads on the speakers and they happened to get pinched when you are installing them (or bent from the factory during delivery / transport), they can cause a short if the leads gets bent enough to touch the speaker housing. This is exactly what happened to my OEM speaker that caused the voltage regulator chip on the sound board to heat up super hot and eventually blow (physically exploded).

2 weeks later
#26 7 years ago

Thanks, gents. I'm using spade connectors for the cabinet speaker and they appear to be completely straight. I've read up on some additional troubleshooting guides to confirm the signal path and biasing capacitors are intact, but it sounds like the amp has an internal short and the hum is an resulting output to the speaker. Still doesn't quite answer why I had to turn the sound level up so high, but I'll check that the impedance is correct for the new speaker configuration. That could have been the cause for blowing the amp in the first place. Thanks for your input!

Promoted items from the Pinside Marketplace
$ 219.00
Gameroom - Decorations
Lit Frames
Decorations

Reply

Wanna join the discussion? Please sign in to reply to this topic.

Hey there! Welcome to Pinside!

Donate to Pinside

Great to see you're enjoying Pinside! Did you know Pinside is able to run without any 3rd-party banners or ads, thanks to the support from our visitors? Please consider a donation to Pinside and get anext to your username to show for it! Or better yet, subscribe to Pinside+!


This page was printed from https://pinside.com/pinball/forum/topic/wpc-sound-board-problem and we tried optimising it for printing. Some page elements may have been deliberately hidden.

Scan the QR code on the left to jump to the URL this document was printed from.