No sound from portable Super Famicom, only video

[KamiFolding]

Hey everyone! New user around here, sorry if this is a noob question.

I'm having an issue with my portable Super Famicom build. For months now I can't seem to get any sound out of it even though my wiring should be correct aswell as me testing on multiple consoles, amplifiers and speakers. And everytime I raise the volume on my audio amplifier the console seemingly restarts itself (which only happens if the amplifier is wired to the same power circuitry as the rest of the setup).

I am using a USB C rechargable 9V battery which supplies power (5V after hitting a regulator) to the SFC (it's an SHVC-CPU-01 model from 1990) through the 7805 pins. My screen is getting power from the same battery but without the use of a regulator.

I am getting composite video output without any major issues, although it having a few weird vertical lines which I suspect lies on my screen generally being kinda low quality (it's one of those cheap car monitors from Amazon).

Anyone here got an idea of what could be the problem? Help would be really appreciated! And if some wiring images are needed I can post them here.

 

[YveltalGriffin]

I had a similar issue recently when testing a new audio amp on a SNES. The peaky current draw from the audio amp on the SNES's 5V rail caused the SNES to brownout and reset.

My temporary fix was adding a large (220uF+) electrolytic capacitor to the SNES motherboard, right next to where the audio amp power wires were connected.

A better option is isolating the audio amp from the SNES 5V rail entirely, by powering it from a dedicated regulator.

 

[KamiFolding]

Hmm, okay.

I just reconnected my setup after powering the 5V audio amp from a powerbank connected with a USB cable instead of the regulator, and now the resetting issue is gone (as mentioned that I tried before), but there's still no sound.

Can you share some images of what exactly you mean with your solutions? Thanks in advance!

 

[YveltalGriffin]

The brownout issue and no sound issue are probably separate. My previous comments were only related to solving the brownout.

Here's how my 1000uF 6.3V cap looks on the SNES mobo. It should be located close to the power input of the audio amp, so it can supply the bursts of current the amp needs. This is just a messy test setup, but in your portable it should be easy to connect the cap across the audio amp power pads or something.

About the no sound issue: does the SNES play audio through the multiout port? Can you share some pics of your audio amp wiring?

 

[KamiFolding]

Yeah, I should probably look into fixing the brownout issue with a better solution, but right now I first wanna get some sound out of it at all.

Here's how my wiring is set up right now. The first image shows the connections made at the SNES Multiout port. There's video out (yellow), audio ground (black),audio left (white) and audio right (red). The audio lines go directly to the input area of the audio amplifier, as seen in the second photo. I've got 2 speakers wired to the audio amplifier aswell (which should be visible on the amps markings).

Before I put the SNES console apart I did get audio out from the console wired to an amplfier and 2 speakers, but then the Multiout connector was still intact (I have desoldered it since), and I was running the SNES through the AC Adapter..

As a side note, I'm relatively new to electronics and this is my first portable ever, so I'm not super used to troubleshooting these kind of issues.

Thanks again!

 

[YveltalGriffin]

Wiring looks reasonable. Some things to try:

Amp:

• Connect a different audio source to the amp, to confirm it works

SNES:

• Wire the SNES audio to a headphone jack, and see if you can hear it with headphones
• Try reseating the sound module, if your motherboard has one
• Measure the sound pins with a multimeter to see if there's any activity
• Check C65 and C66 in case they're damaged or faulty

It's hard to say what exactly is wrong, but this is a classic type of portablizing problem. The best way to tackle it is by getting things to a working state, and then ruling things out one by one.

 

[KamiFolding]

• I have already tried with wiring a GBA consoles speaker output pins to the amplifier, which worked out nicely. I even tried buying a second amp with mono output just to confirm the first one wasn't faulty. So that one is kinda ruled out by now.
• On another console I have (a working PAL SNES) I wired the Multiout sound pins to a 3.5mm headphone jack, and that worked out nicely. Since then I have desoldered some components on that console (namely the RF box, multiout connector, AC barrel plug, C67 capacitor, 7805 regulator, 1A fuse and the reset switch), and when trying the same wiring again (but now by supplying the console power through the 7805 regulator), I got no sound at all, and strangely enough with the same issues as with my SFC build.
• My SNES mobo has a sound module, yes. I have tried reinserting it multiple times to no avail, and I even wen't as far as to try with another SHVC-Sound module from a working console I had, which sadly made no difference. It could also be worth to note that the SFC I am portabilizing right now was working with the same sound module around 6 months ago (before I took the console apart and started on the project).
• I just measured continuity from the sound pins outputting to a 3.5mm audio cable, nothing too notable there. Thanks for the advice though!
• C65 and C66 seem fine, and my multimeter doesn't seem to give me any faulty results when measuring those. And once again, this console was working just before I took it apart a few months ago, aswell as my working PAL SNES getting the same issue when tested leads me to thinking this isn't a cap problem really, but I don't know for sure.

I believe the removal of one of the components mentioned above (the ones I removed from my PAL SNES) could be the reason as to why this issue is happening, so I might need to resolder those one by one to backtrack it to a working state again, as you just said. It could also be so that my entire power setup (a single 500mAh 9V battery) isn't providing enough amps to power up the entire circuit, although I believe this to be pretty unlikely since I still didn't get any sound output when I wired the sound amp to a different source voltage.