Question: Should I be getting audio on the JAMMA output of a Naomi Capcom IO? Or: Why am I getting amplified stereo audio?

[Kujako]

Trying to move from a Chinese knock-off of a Capcom IO board to the real deal. But I'm only getting audio from the RCA output and not on the JAMMA connector... is this "normal"? I was under the assumption that it would work like my knockoff and mix the amplified audio down to mono for the JAMMA and nothing I've been able to find on the interwebs indicates otherwise. Everyone seems to just say plug in the Capcom IO board and go.

 

[skate323k137]

The capcom IO has a JAMMA audio amp. Have you checked the volume pot?

 

[Frank_fjs]

Did you connect the RCA audio output of Naomi to the RCA audio input of the Capcom IO? There's two RCA outlets on the Capcom IO, ensure you are feeding the Naomi output to the Capcom input and not the Capcom output.

Also, did you turn the volume pot up on the Capcom IO?

 

[Kujako]

The capcom IO has a JAMMA audio amp. Have you checked the volume pot?

Yes, and adjusting the pot changes the audio from the output RCS jacks. Nothing from the JAMMA.

@Frank_fjs also yes. I should have said, audio from the RCA outputs is working fine, it's just off the JAMMA that I get nothing.

Looking at the PCB, I can trace the speaker output lines from the JAMMA connector to the amplifier. But I lose it at a pair of funky looking capacitors (marked with arrow)....

 

[Kujako]

So here's where things get weird... from everything I've read, the RCA audio output is supposed to be line level. But I'm getting amplified. I see no signs of modifications to the board, but could someone have somehow switched the amp to the stereo output from the mono on the JAMMA board?

 

[Evan]

So here's where things get weird... from everything I've read, the RCA audio output is supposed to be line level. But I'm getting amplified. I see no signs of modifications to the board, but could someone have somehow switched the amp to the stereo output from the mono on the JAMMA board?

I also get amplified audio out of mine, and mines definitely not been modified. Probably something stock from the factory.

 

[Kujako]

@Evan but do you get amplified audio from JAMMA?

 

[Evan]

@Evan but do you get amplified audio from JAMMA?

Yeah I do

 

[Kujako]

@Evan but do you get amplified audio from JAMMA?

Yeah I do

So then I'm back to the issue of why I'm seemingly only getting audio from the stereo output... going to have to dig out my oscilloscope I think and try to see if I'm getting any audio at all on the JAMMA connector and then trace back to try and find a fault if I'm not.

 

[Evan]

@Evan but do you get amplified audio from JAMMA?

Yeah I do

So then I'm back to the issue of why I'm seemingly only getting audio from the stereo output... going to have to dig out my oscilloscope I think and try to see if I'm getting any audio at all on the JAMMA connector and then trace back to try and find a fault if I'm not.

Yeah that’s odd, my only guess is that maybe we have different revisions of it. I use my Sega io most of the time, so I’ll dig my capcom io back out to make sure that’s the jamma output is amplified

 

[Kujako]

@Evan but do you get amplified audio from JAMMA?

Yeah I do

So then I'm back to the issue of why I'm seemingly only getting audio from the stereo output... going to have to dig out my oscilloscope I think and try to see if I'm getting any audio at all on the JAMMA connector and then trace back to try and find a fault if I'm not.

Yeah that’s odd, my only guess is that maybe we have different revisions of it. I use my Sega io most of the time, so I’ll dig my capcom io back out to make sure that’s the jamma output is amplified

Confirmed with an oscilloscope that I am getting nothing on the JAMMA...

 

[Kujako]

Tracing back from JAMMA pin 10 (speaker+) I encounter this lil guy. I think it's a rectifier diode, but not sure. It also bridges the orange "thing" on the right and also ends up in the amp circuit at the transistor (big one on the heat sink). Another pin off the assumed diode goes to ground, with the center pin opposite the JAMMA connector also going to ground... which seems weird. Anyone have any ideas what the ZDA1 shown is for or is? ZD marking would seem to indicate a Zener Diode...


JAMMA pin L (speaker-) goes deep into the amplifier circuit where I lose it a the transistor.

Edit: Think I mis-traced. The 27A does look to be a Zener Diode. So the top most center pin should be ground, the left closest pin should be input and the right closet should be output to the JAMMA. Will investigate more.

 

[Kujako]

Update: I now have a second board of the same revision to compare against and it is working as expected with amplified audio on the JAMMA. I’ve traced the audio out pins back to the two yellow shiny components which upon testing would seem to be diodes not capacitors as I first thought. Not sure where to go from here...

 

[Evan]

Yeah you’re kinda in a pickle

 

[Kujako]

Yeah you’re kinda in a pickle

I'm thinking I need to check the output of the solid state amplifier as that seems next in line from the diodes. The diodes themselves test as working, giving around a -5v drop using my multimeters diode testing function. Guess I could hook up an oscilloscope to the amp itself (Toshiba TA8201AK). Just need to figure out the pinout (although I can trace from the diodes to the pins used on the JAMMA output).

Edit: Think I'm just gonna replace the TA8201AK and see what happens. They do fail, and they're cheap enough.

 

[Kujako]

So turns out, I can't get the TA8201AK off the heatsink and I can't desolder the heatsink cause its a heatsink... going to have to come up with some sort of solvent to remove the thermal pad. It's on there really gud.

 

[Kujako]

Only took me three months, but I got the TA8201AK replaced and all's working correctly now. That little thing was on there gud... but managed to dissolve the thermal pad adhesive with isopropyl and then desolder it. Slapped in a replacement with some arctic silver thermal paste and it's done. Bit of flux residue left (yellowish because I use a bees wax flux compound so the deadly fumes smell better). At this rate I'll have all projects off my workbench... never.