Blast City Sound Issue

PCB problems and fixes
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Beaps
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Blast City Sound Issue

Post by Beaps »

Hi Guys.

OK so my friend has just got a Blast City & he is new to the Candy cab scene. He said the sound from any PCB is only coming out the right hand speaker only. The person he got it from said something like there is a sound amp inside but its not connected so the volume dial under the CP does nothing?

The cab has both the JVS & Jamma loom if that helps.

So I am gonna pop over to his tomorrow to have a look at it for him I just wanted to ask a few questions.

- Where is the sound amp located on these machines?
- Why do you think its playing from 1 speaker if the sound amp is not connected?
- Where does the volume pot under the CP lead to?

Any help is appreciated.
B
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hedorah
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Re: Blast City Sound Issue

Post by hedorah »

The sound amp on Blasts are actually inside the PSU cage. Not sure why sound would be coming out of one speaker, one of the more technically proficient members will probably have better answers for you.
Asure
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Re: Blast City Sound Issue

Post by Asure »

If the jamma edge is wired for neo-geo, you will have speaker+ (right), and speaker + (left) on pins L and 10.
Usually this means you will have sound only on the right speaker when using a normal jamma board. (The left speaker is connected to ground & ground this way, never gets a signal.)

But, this is assuming the cab was wired at the jamma edge for stereo/neo-geo MVS at some point.

In a normal true jamma setup with two speakers, the wires for speaker+ go to pin 10(parts), and wires for speaker- go to pin L(bottom).
See here for a jamma vs. neo pinout of the edge connector.
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Beaps
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Re: Blast City Sound Issue

Post by Beaps »

Thanks for your help guys...

On a 4 slot its still only coming out the right hand speaker the same as it does for a Jamma PCB?

Also any idea why the volume dial under the the CP does nothing?

Thanks
B
Asure
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Re: Blast City Sound Issue

Post by Asure »

As for the sound on only one speaker

- Check the wiring to the speakers
- There should be two wires for each speaker, positive+ & negative - (usually grounded, depends on cab/amp/setup etc.)

Two speakers, if wired for jamma
- Both speaker + wires are twisted together and soldered onto jamma edge pin 10 (SP+) (parts side)
- Both speaker - wires are twisted together and soldered onto jamma edge pin L (bottom)
- Optional, the speakers - wires are soldered to GND instead of pin L (i've seen this on several cabs)
- Note speaker impendance should be about 8 Ohms alltogether.
- You can use them in parallel like this, but the amp on your game pcb must be able to handle it. Don't crank it up too loud :)

Two speakers, if wired for MVS multislot stereo
- Right speaker + to pin 10, left speaker + to pin L
- Both speaker - wires twisted together and tied to GND

As your post didn't point out what kind of board is connected, troubleshooting stops here :)
All i can conclude from the MVS being 'right only' is that it _may_ be wired for jamma instead of MVS.
So you really need to find out which wire(s) go to the speakers and sort them out with a soldering iron :)

As for the volume dial, this is bypassed. Normally the wiring goes from jamma edge into the cab's internal amp, dial, then to the speakers.
But it seems the previous owner already bypassed the cab's internal amp (and the volume dial). Worst case scenario the internal cab wiring/amp is shorted out which could be the cause for single speaker audio. But, just check the wiring first. :)
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Beaps
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Re: Blast City Sound Issue

Post by Beaps »

Brilliant stuff!!

OK thanks for the info, I will let you know how I get on, THANKS!

Just one last thing, if it is the amp that is faulty when I have checked the wiring, is that located in the whole machines power supply?
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Jaelus
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Re: Blast City Sound Issue

Post by Jaelus »

Beaps wrote:Just one last thing, if it is the amp that is faulty when I have checked the wiring, is that located in the whole machines power supply?
It's in the power supply casing. On the back of the machine you'll see a brass panel. Unscrew the edge screws and it slides out the back of the cab (it's got a quick connect in the cab so it will disengage easily). Once it's out of the cab, open up the casing and you'll see the amp inside there. It's a good opportunity to clean it at that point since they tend to get full of dirt, and also replace the fan if it looks suspect.
My feedback from the neo-geo forums:
http://www.neo-geo.com/forums/itrader.php?u=10822
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Beaps
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Re: Blast City Sound Issue

Post by Beaps »

OK so here is how it went down.

I looked over he machine & the L/R speakers are wired directly to the Jamma edge with both grounds connected. PCB play fine now in mono but the volume is controlled from the board :shifty:

If I hook up a 4 slot the sound is not playing in stereo until I do the below

- Right speaker + to pin 10, left speaker + to pin L
- Both speaker - wires twisted together and tied to GND

So going forward if I play say Final Fight then I have to set it up one way for Jamma & if I want to play MVS I have to swap the wires to get stereo, is that correct?

Thanks again for the input.
Asure
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Re: Blast City Sound Issue

Post by Asure »

Beaps wrote:OK so here is how it went down.

I looked over he machine & the L/R speakers are wired directly to the Jamma edge with both grounds connected. PCB play fine now in mono but the volume is controlled from the board :shifty:
That's pretty normal, most jamma boards have mono audio only. However, there are some games that have a header/connector on the pcb itself, which outputs stereo.
Beaps wrote: If I hook up a 4 slot the sound is not playing in stereo until I do the below
- Right speaker + to pin 10, left speaker + to pin L
- Both speaker - wires twisted together and tied to GND
That's also 100% correct, you need to rewire everytime .. ugh.
Beaps wrote: So going forward if I play say Final Fight then I have to set it up one way for Jamma & if I want to play MVS I have to swap the wires to get stereo, is that correct?
No i was kidding. You could re-wire the left & right speaker into the cabs original amp, then wire up the RCA jacks.
Here's the deal, i don't own a Blast City, but googling around, it seems the on-board amp should have two RCA male plugs coming out of it, and nothing going into the jamma edge, as far as i can tell.
Obviously those two RCA jacks won't get you sound on many jamma games, but will work as-is for games that have audio on RCA out.
So i can understand why the previous owner rewired the cabinet for jamma, and controls the audio by the games volume pot(s) :)
This is the normal way that most standard jamma mono cabs have audio wired. Sometimes there is an additional volume control in between as well, but that's it. Mono forever ;)

Restoring your audio
Some more googling finds me this page. He writes the following:
Web page wrote:Here is the I/O harness. The far left connector labeled CN5 is supposed to have 4 wires at the top of the connector that end in RCA plugs for stereo sound. My connector is missing these wires. Above I mentioned that there was a white piece of paper that apparently said the sound wasn't working.
There are four black holes in the connector that's plugged into CN5. So i guess two grounds & L+R plus.
And more googlin finds his post at AO explaning the pinout for CN5. He added two male RCA jacks to the CN5 connector.

When you have that sorted out, this guy at neo-geo.commakes cables that will fit and then your cab will be most compatible with all sorts of audio :)
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