No Jamma (Mono) sound in my Sega Blast City. Help! No idea.

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OldFoo

No Jamma (Mono) sound in my Sega Blast City. Help! No idea.

Post by OldFoo »

So, I have a rather annoying problem with my Sega Blast City cab I got recently.



First of all, the was originally a Sega Bass Fishing cab, the ones sent over to America. It was converted into stock condition. Originally model 3. Wiring harness was changed some to work with a Naomi set up. Like, the JST connector for stereo audio was removed and RCA connectors were spliced in to hook up to the Naomi motherboard, etc. So here is my problem:



When hooked up to my Naomi 2 set up with GD-ROM, works fine, I can hear audio when connected through the RCA, both speakers play and sounds great. My problem comes when I try to plug in just a pure Jamma based PCB, like Esprade for instance. Anything with mono sound. I get no audio at all.



Now, I have a sound card amp inside of my power supply. I see on the sound card amp where it has "M" and two wires coming out for mono. I have traced those wires all the back to the main board/control board (Not sure what to call it? Its mounted on the side of my coin box inside.) All the wires look good, and I see nowhere where it could not be getting a connection. I see the Speaker+ and Speaker- on my Jamma harness, both look good and connected from there back as well. I just can't understand why I'm getting no sound through the harness if everything is hooked up.



I thought perhaps the mere presence of the RCA is giving enough resistance or something at the sound card that when its getting a mono signal it doesn't know when to switch over? It seems like everything is hooked up fine, its just not "switching" over to mono sound. I've checked everywhere I know to in the cab for any sort of dipswitch or the sort to get it into mono with no luck unless I missed something. I am at a complete loss and any help at all would be appreciated. Especially by people who understand the original set up of these Sega Bass Fishing cabs.



So, this is my idea to fix it unless I get a better one:



Take the RCA connectors, splice them into the Speaker+ and Speaker- on the jamma connector. Then do some sort of set up to get them running out of both speakers (y-splitter sort of deal). Then, wire in some sort of switch for them so that in one position it will be "on" have a full connection to the jamma connector, and so mono sound would flow through the cable. Then, have a "off" where it would cut the connection and just have the cable with the RCA connectors standing alone, so I could use it for my Naomi set up still. As far as I can understand, the signal should go through the cable and get audio. I assume its line-level since it has the amp.



Though I am worried if by feeding the mono sound into those cables, running back into the setero connectors on the sound boad amp, it may mess it up the sound card? Or perhaps just blow the speakers? I really don't know but this is my best idea so far to get mono sound when I play my jamma games.



So, does anyone have any ideas or things I can try to get this to work? I am at a complete loss. I would even pay someones gas and such if you lived nearby to come look at it, I just don't know what to do at this point, stumped. I have all these arcade PCBs just waiting for me to play



Thanks for reading and any help is appreciated!



I can also provide pictures of whatever is requested if that may help diagnose.
OldFoo

Post by OldFoo »

Phew.. a lot of info..



A few pointers:



- JAMMA boards have a built-in amplifier. The output of a JAMMA board must not be routed through an amp.



- Naomi lacks an amp, so either the I/O (capcom) has one, or an amplifier in the cab is used (hence the RCA connections).



- When fiddling with wires, switches, etc: keep in mind that JAMMA requires the speaker setup to provide 8 Ohms of impedance. Wiring speakers incorrectly can damage the onboard amp on a JAMMA pcb.
OldFoo

Post by OldFoo »

has this got the model 3 to JAMMA harness in it, as I think the speakers connector has 2 plugs inline, one that is used for JVS side, and one that is for the JAMMA side, you have to unplug that and switch it?
OldFoo

Post by OldFoo »

Cageman wrote:Phew.. a lot of info..



A few pointers:



- JAMMA boards have a built-in amplifier. The output of a JAMMA board must not be routed through an amp.



- Naomi lacks an amp, so either the I/O (capcom) has one, or an amplifier in the cab is used (hence the RCA connections).



- When fiddling with wires, switches, etc: keep in mind that JAMMA requires the speaker setup to provide 8 Ohms of impedance. Wiring speakers incorrectly can damage the onboard amp on a JAMMA pcb.


Indeed lol, I like to say as much as I know so that I don't leave anything out. I was sorta afraid of that, looks like my idea would suck then. My cab has a amp, inside the power supply. I also have a separate sound amp I picked up. Heres a picture of it on the board I got.



Image



I did not know about the 8 Ohms, thanks for telling me, I will keep that in mind :D.


englishman_in_plantcity wrote: has this got the model 3 to JAMMA harness in it, as I think the speakers connector has 2 plugs inline, one that is used for JVS side, and one that is for the JAMMA side, you have to unplug that and switch it?


This originally had the model 3 harness and it was converted via mod to Sega 001 spec by the guy who owned it before me. When you say speakers connector do you mean where it actually connects on the speaker or elsewhere in the cab? Thats the only place I haven't looked in much detail yet, is at the actual speakers and how the connect, since it would require pulling out the monitor to really get a good look.
OldFoo

Post by OldFoo »

Also, I was thinking today. You know, since jamma audio already has its own built in amp. What if I was to just wire directly from the speaker+ and speaker- of my jamma connector to both of my speakers, left and right? In a ideal set up since it already has its own built in amp when using jamma, I assume the speaker+ and speaker- just run directly to a speaker?



Then, I could do the whole switch idea but at the actual speaker connection, so I could have it hooked up directly for mono, then switch it easily to the original wiring for stereo sound through the RCA?
OldFoo

Post by OldFoo »

Otoko no Zenyou wrote:Also, I was thinking today. You know, since jamma audio already has its own built in amp. What if I was to just wire directly from the speaker+ and speaker- of my jamma connector to both of my speakers, left and right? In a ideal set up since it already has its own built in amp when using jamma, I assume the speaker+ and speaker- just run directly to a speaker?



Then, I could do the whole switch idea but at the actual speaker connection, so I could have it hooked up directly for mono, then switch it easily to the original wiring for stereo sound through the RCA?


Yes, you can hook the speakers directly to the JAMMA harness. Be aware of the impedance, though. Google a bit to find out more about how to connect speakers. First, check the impedance level of the speaker itself (printed on the rear of the speaker).



Also, before trying to do this, check if the speaker connection is routed to the amp using a seperate (in-line) connector. My cab is wired that way: I can just switch the speakers from the AMP to the JAMMA harness by disconnecting the speakers from the amp, and connecting them to the JAMMA harness.
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