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[Solved] Need help fixing VRC7 Audio

Posted: Wed Mar 25, 2020 2:17 am
by Ice Man
I just recently got a Lagrange Point myself and put the English translation on it.
While the game works well and can be dumped properly, I cannot get the audio to work on my Famicom.

I have done several Lagrange Points and all of them had the audio working.

Does anyone know how to fix it or what IC to replace (and ideally also their name).

Thanks!

Re: Need help fixing VRC7 Audio

Posted: Wed Mar 25, 2020 10:18 am
by Memblers
In case the "hybrid IC" failed, there is a schematic of it here:
viewtopic.php?f=9&t=4709
It potentially could have a cracked solder joint, or a broken or corroded trace on the board. Not so easy to fix when it's coated in epoxy, though..

Re: Need help fixing VRC7 Audio

Posted: Wed Mar 25, 2020 10:35 am
by Ice Man
That schematic helps alot.
I assume JRC 2904 is the OP amp used? In that case, NJM2904 is the same, right?

Also, what exactly does the 3.58MHZ crystal on the VRC7? If it's related to the sound (ADSR).
Can it cause silence, too, if not working properly? Or what is it used for?

Thanks for the help so far!

Re: Need help fixing VRC7 Audio

Posted: Wed Mar 25, 2020 11:16 am
by lidnariq
It's the clock for the VRC7's audio. If it's not working you won't get any sound.

You should be able to bodge in a wire from M2 instead: all the sounds will be an octave too low but otherwise it might work. I think. Unless that slows down register access times too much.

Re: Need help fixing VRC7 Audio

Posted: Wed Mar 25, 2020 11:30 am
by Ice Man
I do have certain sound effects and music, just not the expansion audio. So I guess the crystal is working, at last.

Will try to remove the epoxyd from the circuitry.

Re: Need help fixing VRC7 Audio

Posted: Wed Mar 25, 2020 11:37 am
by lidnariq
Lagrange Point plays almost all the entire soundtrack using the VRC7 (although it uses the 2A03 audio for drums). Sound effects come from the 2A03.

Re: Need help fixing VRC7 Audio

Posted: Wed Mar 25, 2020 11:44 am
by Ice Man
I see. So first step would be to replace the 3.58MHz?
Where would I connect M2 to? XIN (Pin 17)?
What about XOUT (Pin 18)?

Just to test if that would get anything to work, of course.

Re: Need help fixing VRC7 Audio

Posted: Wed Mar 25, 2020 12:05 pm
by lidnariq
Yeah, try connecting M2 to XIN.

Before that, if you have access to a longwaveshortwave radio (or an oscilloscope...), you could see if you can tune it to 3.579MHz and hold the antenna near the cart while it's powered, and see if you get any signal. (You shouldn't hear much, because the crystal frequency and amplitude shouldn't be changing, but it should be able to pick up whether the crystal is going at all.)

Re: Need help fixing VRC7 Audio

Posted: Wed Mar 25, 2020 12:08 pm
by Ice Man
Removed the crystal, connected M2 to Pin 17 (XIN) but still nothing. :(

Afraid I don't have an oscilloscope. Really should buy one one day.

Attached pictures of the PCB just in case.

Re: Need help fixing VRC7 Audio

Posted: Thu Mar 26, 2020 6:07 am
by Ice Man
Bought nrew 3.58 MHZ resonators. Let's see if that's the cause.

If it isn't, I already prepared new boards to replace the sound circuitry.

I just hope the VRC7 itself isn't faulty.

[Solved] Re: Need help fixing VRC7 Audio

Posted: Fri Mar 27, 2020 5:05 am
by Ice Man
Update: The cart is working fine now. It wasn't faulty at all but the AV mod was done wrong.

My Famicom is a HVC-CPU-07 and I grabbed sound directly from the SND pad instead of pin 46 of the connector resulting expansion sound not work.
Everything is fine now.