Mortal Kombat 2 pcb sound issues

[retrogamingjohnny]

Hi everyone. I mentioned this in another post, but I think I just talk about it here since I got a video showing it as well. The issue regards to a Mortal Kombat 2 pcb set that I acquired recently. I had it hooked up and everything. The picture and gameplay is perfect. However, I get a humming sound as you can hear from the video. The sound board is getting power as you can see the LED is on. https://www.youtube.com/watch?v=EBxjin0 ... e=youtu.be
I have already went to the test menu and the soundboard passes the test and I have also set the volume to highest, but the problem is still there.
Any ideas what is wrong? Thanks for any input.

[Zets13]

Video is private, can't watch it.

Just a hunch, but are you running this on an Astro City?

[retrogamingjohnny]

Video is private, can't watch it.

Just a hunch, but are you running this on an Astro City?

Sorry about that, I forgot to publish it. It's view able now. No, it's running on a supergun which you will see on the video. My supergun works perfectly with all my other games, including Robocop, Neo Geo Mvs, CPS2 system. I get sound on all of them, but with Mortal kombat, I get a buzzing sound. I just checked the big capacitor on the soundboard and got a reading, so it works. I don't know what is the issue. Anyone can comment?

[Zets13]

Do you have the -5V connected at your PSU? I have an MK3 PCB (which isn't the same as MK2, I know, but based on the MK2 manual the sound board needs -5v) and when I run it on my Astro City (which has a weak -5v output), I don't get sound, actually I THINK I get a buzzing sound too. When connected in another cab which apparently has sufficient -5v I get sound just fine.

I'd wager that that might be your issue.

[retrogamingjohnny]

Do you have the -5V connected at your PSU? I have an MK3 PCB (which isn't the same as MK2, I know, but based on the MK2 manual the sound board needs -5v) and when I run it on my Astro City (which has a weak -5v output), I don't get sound, actually I THINK I get a buzzing sound too. When connected in another cab which apparently has sufficient -5v I get sound just fine.

I'd wager that that might be your issue.

I believe so. The label notes it has -5 although I am not sure if the rating is good enough. Do you know?


The LED on the soundboard is on, but still no sound. I guess that doesn't proves it's getting -5v or enough of it.

Can you specify what it means by sufficient -5v?

I am actually waiting for a new arcade supply that I just ordered. It has -5v. I think it's the only way to make sure whether the sound works.

[Ed Oscuro]

Brand looks kinda suspicious to me. And actually even if it's working according to spec, that's not a lot of juice on the -5A rail (at least in PC terms - I don't know what qualifies as lots of power in JAMMA land; 850mA is what your standard SNES power supply can provide). Lotsa power on the 12V rail though.

[Zets13]

Try measuring the -5v with a multimeter at the JAMMA edge (or I guess between the main PCB and the sound board). I'm not sure what it needs to run properly, though, so you might want to check and see if the specs of the MK2 cab's PSU are in the manual which you can find online. Even so, if the reading you get with the multimeter is well below -5v then that could very well be the issue. As I said I am pretty sure your problem with the MK2 is similar to the problem I had with my MK3 until I hooked it up to a better -5v source. If the new PSU doesn't resolve the lack of sound, then you can look into a Negatron device - I haven't used one but I've heard some suggest it in instances like these.

[retrogamingjohnny]

Ok I made a discovery that now I am quite certain what the problem is. You guys were right. There is indeed no -5v coming from the ATX power supply. I found out and it is quite obvious. Look at the picture of the molex connector of the PSU

See that empty hole on the upper right? That is pin 18 and is supposedly -5v, and somehow it is the only pin that is missing a wire. It is just empty even though the label says it supplies -5v. Details about the PSU pin outs are detailed here http://pinouts.ru/Power/atxpower_pinout.shtml.
Something interesting that I did even though it was a mistake since I belived that pin 8 was also -5v, so I used a jumper and linked pin 8 to 18 and the result was total silence. There was no more buzzing sound but just silence.
Now I guess the only thing left to do is wait for my arcade power supply, which has -5v and hook it up to the supergun, now that we know it is not getting -5v at this point.

[retrogamingjohnny]

Try measuring the -5v with a multimeter at the JAMMA edge (or I guess between the main PCB and the sound board). I'm not sure what it needs to run properly, though, so you might want to check and see if the specs of the MK2 cab's PSU are in the manual which you can find online. Even so, if the reading you get with the multimeter is well below -5v then that could very well be the issue. As I said I am pretty sure your problem with the MK2 is similar to the problem I had with my MK3 until I hooked it up to a better -5v source. If the new PSU doesn't resolve the lack of sound, then you can look into a Negatron device - I haven't used one but I've heard some suggest it in instances like these.

Yes, I did that and indeed there is no reading coming from the -5v at the jamma edge. The ATX power supply is not providing any -5v. You were right. Now I am certain that is what is causing the problem.

[Zets13]

Something interesting that I did even though it was a mistake since I belived that pin 8 was also -5v, so I used a jumper and linked pin 8 to 18 and the result was total silence. There was no more buzzing sound but just silence.
Now I guess the only thing left to do is wait for my arcade power supply, which has -5v and hook it up to the supergun, now that we know it is not getting -5v at this point.

Does everything still check as OK on the soundboard after this? Just hoping you didn't inadvertently damage something.

[Asure]

Negatron would be the easiest solution to this problem.



No need to hack up the power supply. Hope you didn't burn out something by adding +5 to the -5 input.....

[retrogamingjohnny]

Something interesting that I did even though it was a mistake since I belived that pin 8 was also -5v, so I used a jumper and linked pin 8 to 18 and the result was total silence. There was no more buzzing sound but just silence.
Now I guess the only thing left to do is wait for my arcade power supply, which has -5v and hook it up to the supergun, now that we know it is not getting -5v at this point.

Does everything still check as OK on the soundboard after this? Just hoping you didn't inadvertently damage something.

Yes. I just re checked and everything passed. Thanks lord. That was too reckless.

[retrogamingjohnny]

Negatron would be the easiest solution to this problem.



No need to hack up the power supply. Hope you didn't burn out something by adding +5 to the -5 input.....

Yes, I heard about it on YouTube. I'll try with my new power supply when I get it since I have everything that I need. If, anything I will try this.

[keropi]

are the Negatron's specs fine for audio applications or it's just an "OK" solution to the -5v problem? (meaning it doesn't produce noise that passes through the sound amps that need -5v)

edit:
on another forum about old pcs, a knowledgeable person told me it was better to use a LM7509 to get -5v from the -12v line of an ATX PSU, since it's better regarding noise "("~100mV typical" according to the negatron web site... vs 0.125 mV from the 79xx datasheet )" and way cheaper. Anyone looked into that?

[retrogamingjohnny]

I solved the sound problem! The problem was indeed no -5v. The new arcade power supply arrived and I wasted no time. I hooked it up, made sure all the wires are in the right place, tested it with a voltmeter, and tested it with a pcb. I tested it first with my neo geo mvs first and noticed that the picture quality is the best I've seen on the boards even though I'm running it through a different power source. Now I can test it with MK2. See for yourself
http://youtu.be/gKUrF0V-als
I was so happy I could jump off a building.
So there it is. The only remaining issue is the CMOS error, which I was told I simply need to replace the watch battery. So stay tune.

[retrogamingjohnny]

I changed the lithium battery and the CMOS issue is gone. All issues related to this game has been resolved. Thanks everyone for your help.