Mortal Kombat 2 Sound Board repair

[mecha]

are you getting amplifier hiss from the speakers? there's an auxiliary out on the sound board that outputs un-amplified audio... if you wanna be creative you can get like an RCA jack from radio shack to tap into that to at least see if it's making sound... if it's unamplified you can safely plug it into a TV. or actually I think there's a spot you can tap in to get amplified audio too... but don't quote me on either lol

I say to go this route because it could be any number of wiring issues. to my understanding, the sound board piggybacks the audio wiring back to the JAMMA edge through the wiring harness that connects to the sound board. you can even see in the pinout that it says like Audio + and Audio -.

 

[action76]

I am getting amp hiss so I think the amp is fine. I have caught myself trying to see if anything was coming out of the aux out connection by holding some wires on there that were hooked to a speaker but I am going to try again with a little better setup and something that is amped to make sure it is load enough to hear if something is getting output there.
Thanks

 

[mecha]

well if you have amp hiss then I doubt it's anything with your wiring.

weird.

did you check the volume setting? you should still get a BONG with the volume turned down, I think.

 

[WindDrake]

Use a speaker or old set of headphones and check out the amp IC/preamp out for unamplified bong/noise.

Admittedly I'm pushing my ability to diagnose now, without physically touching the unit.

Your sound CPU being bad wasn't a huge surprise, now it looks like the board is having issues booting. According to the schematic, it should be an ADSP2105.

Your core/graphics CPU is the TMS34010-50. http://focus.ti.com/lit/ds/symlink/tms34010.pdf

Check out PDF page 45/46 of the MK2 Manual.

The TMS34010 looks like it's looking for a clock signal, and there's some voodoo going on at U21 with the system's 3 primary crystals (50mhz, 25mhz, 8mhz). I think they are using the FlipFlop do divide the 50mhz clock signal into 25mhz.

U21 is a Dual D FlipFlop that's handling ALL of your clock signals.

Check pin 5 of U21 for 25mhz, Pin 3 for 50mhz, and 8mhz at Pin 11.

Also check pin 5 of the TMS34010 for 50mhz.

MAX691 CPU Supervisor: http://datasheets.maxim-ic.com/en/ds/MAX690-MAX695.pdf

The MAX691 CPU Supervisor at UH6 could also be holding RESET down, so check pin 15 to see if the ACTIVE LOW reset line is at ~+5v (Pulled high through R152).

 

[action76]

Thanks for the responses. Let me back up and tell you what all I have done. First I know the mainboard works fine. I have hooked it up with a working sound board and it all works great. I have taken the ROMS off the bad board and put them on the good board and the good board works fine with the other ROMS. So I know the ROMS are good and now with the "new" CPU the board seems to be behaving like it should as far as the LED coming on and staying on. There has got to be something else wrong on the sound board. My buddy and I were looking at it today and he said the mute circuit might be malfunctioning and stuck on mute. He said he thought that pin 6 of U16 was the mute??? If not that it seems the audio signal is dying somewhere before it gets to the speakers.
Does any of that make any sense?

Thanks

 

[Magog]

I wish I would have seen this earlier. I had about 5 dead MKII soundboards I would have gladly sent to you to play with. Goodluck I hope you can make it work.

Andrew

 

[action76]

Had huh? As in, not anymore? Just my luck! Thanks anyway, I would have definitely taken you up on the offer.

I wish I would have seen this earlier. I had about 5 dead MKII soundboards I would have gladly sent to you to play with. Goodluck I hope you can make it work.

Andrew

 

[Magog]

Had huh? As in, not anymore? Just my luck! Thanks anyway, I would have definitely taken you up on the offer.

Pretty sure I ended up giving them to a fellow KLOVer a while back...I might have a couple left. I am on vacation from work this week starting tomorrow, family in town. I will try and look tomorrow if I have time if not when I get back I will check my MK stash.

 

[WindDrake]

Hm. With the new CPU on the sound board, are you getting graphics? Can't really tell by your post, figured it's worth asking.

If it's getting graphics and no sound, then I'll have to dig out the schematics again and chase back audio generation.

 

[action76]

Pretty sure I ended up giving them to a fellow KLOVer a while back...I might have a couple left. I am on vacation from work this week starting tomorrow, family in town. I will try and look tomorrow if I have time if not when I get back I will check my MK stash.

That would be awesome. I really appreciate it. Just PM me when you know something. This has become one of those "I'm not going to let this thing beat me" situations. I hope to figure out the fail points of these things and hopefully be able to help some other people fix theirs too.
Thank you.

 

[action76]

Hm. With the new CPU on the sound board, are you getting graphics? Can't really tell by your post, figured it's worth asking.

If it's getting graphics and no sound, then I'll have to dig out the schematics again and chase back audio generation.

Yes, it is getting graphics and plays fine, just with no sound out of this sound board..

 

[WindDrake]

Ok, chasing that circuit back, then. Starting at page 74 of the MK2 PDF.

Audio Amp: Fujitsu MB3731 http://datasheet.octopart.com/MB3731-Fujitsu-datasheet-104990.pdf

Pin 6 is mute. If it's short to ground, the amplifier is muted. Check C2 (47uF, 20%, Axial Leads). The pin should read some voltage because of the Amp IC's internal pull-up resistor.

C106 is your decoupling cap. You can check at the Anode (+) of the cap with a pair of headphones/crystal earpeice/etc set up to probe and listen for audio. Don't try that at the Cathode (-), because there's DC voltage there that will let the magic smoke out of your headphones/earpiece/etc.

 

[action76]

Ok, chasing that circuit back, then. Starting at page 74 of the MK2 PDF.

Audio Amp: Fujitsu MB3731 http://datasheet.octopart.com/MB3731-Fujitsu-datasheet-104990.pdf

Pin 6 is mute. If it's short to ground, the amplifier is muted. Check C2 (47uF, 20%, Axial Leads). The pin should read some voltage because of the Amp IC's internal pull-up resistor.

C106 is your decoupling cap. You can check at the Anode (+) of the cap with a pair of headphones/crystal earpeice/etc set up to probe and listen for audio. Don't try that at the Cathode (-), because there's DC voltage there that will let the magic smoke out of your headphones/earpiece/etc.

I think all of that is ok then. I checked C2 and the voltage is 3v. There is no sound at C106. I moved back to C100 where I believe this would be unamped and I am getting nothing either.

Is there a way to check what is coming in to U16 on pin 7 which is Data, 6 which is is a LTCH, and 5 which is a CLK. I am wondering what data if any is geting to that point?

 

[WindDrake]

Well, U16 is the AD1851 DAC. http://www.analog.com/static/imported-files/data_sheets/AD1851_1861.pdf

Looks like U37, a TL084 JFET Op-Amp is involved, also. http://focus.ti.com/lit/ds/symlink/tl084.pdf

So, lets figure out if it's the JFET Op-Amp (Filter Circuit) or the DAC.

Take a listen at the Anode (+) of C100 or Pin 9 on the AD1851 (DACOUT). If you hear audio, then I can say with almost certainty that the TL084 is shot and needs to be replaced.

If you can't hear anything on DACOUT, we'll have to check out the DAC and audio generation circuit itself.

 

[action76]

I am getting nothing from pin 9. I also tried C100 just to be safe. So it looks like the DAC or audio generation circuit.

 

[WindDrake]

Ok, lets see...

Pin 7 is DAC Data on the AD1851. Check it out with a Logic Probe in 3.3v/CMOS mode. You should see flashing, which means the DAC is recieving data from the ADSP2105.

Pin 6 is the enable latch for the AD1851 (Active HIGH). You should see voltage here. U38, a Schmitt Trigger, has an inverted output, so it takes a LOW and turns it into a high. Pin 1 of U38 should be LOW and pin 2 (Latch) should be HIGH. The Resistor and cap before it are just a simple R/C Delay.

You should also see a Clock Signal on pin 56 on the ASDP2105 (DAC_CLK) that goes to pin 5 of the AD1851. I'm not totally sure (hard to read this part of the schematic) but it looks to be in the 11.5-13mhz range.

If U38 pin 1 is LOW and pin 2 is LOW or floating, then the trigger is bad. If U38 pin 1 is high, then we need to chase down the latch circuit. Honestly at this point it's looking more and more like a bad DAC.

 

[action76]

OK, Here's the latest results...

Pin 7 on the AD1851 (U16) is flashing so the DAC should be getting data.

pin 6 on the AD1851 was low. Which I guess means it is not active.

pin 1 of U38 is high and pin 2 is low which, according to what you said, is opposite of what it should be.

So I guess its the latch circuit or a bad DAC then. Where is the DAC. Is it an IC or section? I am having trouble locating it on these schematics.

Also thanks for all this great help!

 

[WindDrake]

Big Edit:

The DAC itself is a chip, it should be a 16-pin plastic DIP.

So, it looks like there's something up with the ADSP again, if you don't have a high coming out of 53. If you do, it looks like there could be a broken trace.

Edit: Specifically, looking at the Datasheet for the ADSP, it takes up one of the serial ports to speak to the DAC. The serial port could be bunk.

More Reading was done, and actually, they are tying Serial Frame to the Latch line. Weird terminology differences, but it's all the same. The ADSP goes Logic Low to signal the beginning/end of a frame. They flip this through the Trigger to a HIGH which the DAC sees as a frame start/end.

Check out that pin with your Logic Probe. You should see it flashing, actually. If it never moves, the serial port on your ADSP is shot.

 

[action76]

Ok I will check this out. It will be tomorrow though. It would be my luck to have gotten two bad CPUs. I guess I could try the CPU in the sound board that I know is working. I am just afraid something would get screwed up on it or the bad CPU would burn something out.

 

[WindDrake]

One of the things you can try to make sure the DAC isn't holding frame/latch down is to lift that leg of the ADSP, and then Logic Probe it while the unit is running to see if latch starts cycling again. If it does, the DAC is the actual problem.

An easier way to do this would be to remove the resistor at R45, then logic probe the ADSP side of that set of connections. That way you don't have to bend pins.