Super Famicom low audio

[jperryss]

Hi all,
I have an original SFC with very low audio on the left channel. I actually can't hear anything from that channel in-game, but I tried a hardware test rom and confirmed that the audio is just very quiet on that side.

Any suggestions on what to check? If it doesn't end up being too difficult of a fix, I might try it myself, otherwise I'll need to find someone to ship it to.

Thanks!
JP

[RP2A03]

What happens when you plug the left cable into the right jack, and the right cable into the left jack? Is the sound coming from the right speaker now low?

Also, this should be in Technical and Restoration.

[jperryss]

What happens when you plug the left cable into the right jack, and the right cable into the left jack? Is the sound coming from the right speaker now low?

Also, this should be in Technical and Restoration.

Thanks, I missed that forum somehow when trying to figure out the best place to post this. Maybe a mod can move it for me.

The TV only has one speaker. I tried swapping L/R jacks at the TV, tried plugging in just the left channel, and also tried a different multi-out cable. In all tests using a SNES Hardware Test rom, the left voice announcement is very quiet and I can barely hear it unless I have the TV volume almost maxed out.

[RP2A03]

If you have an RF switch, try using that. Otherwise, compare the voltages coming out of R67 and R70. They should be the same when both channels are at the same volume.

You can find schematics here: https://dl.dropboxusercontent.com/u/36237540/SNES/jwdonal/schematics/snes_schematic.zip

[jperryss]

Thanks. I do have a DMM, but...

https://dl.dropboxusercontent.com/u/433791/noidea.jpg

Probably best that I leave this to repair to someone that does. :)

[RP2A03]

Thanks. I do have a DMM, but...

https://dl.dropboxusercontent.com/u/433791/noidea.jpg

Probably best that I leave this to repair to someone that does. :)

We all got to start somewhere. If you want to learn I can try to help.

[AdamAnt316]

DMMs are fairly easy to use. Here are a few pointers which should help you get started:

1. Be VERY careful when measuring places where high voltages may be found! Not really applicable to a Super Famicom, since the highest voltage you're likely to see is 10V, but definitely something to keep in mind when using a DMM (or analog VOM). This leads me to my next point:

2. Make sure the probe tips are touching where they're meant to touch. Sometimes, probe tips can slip and short out something, which can be bad. There are probes available which have spring clips to hold them securely to the components being tested.

3. Make sure the setting is correct for what you're trying to measure. Simple, I know, but measuring a DC circuit with the meter set to AC can skew the readings. Generally, the voltages you find inside a Super Famicom are going to be DC, though certain things (like audio signals) tend more towards AC. Speaking of voltage:

4. Make sure the power is turned off before trying to measure resistance! Trying to measure resistance with power applied could damage your meter. To be sure, once power is disconnected, briefly connect a wire between the center pin of the power connector and ground (for example, the screw which holds the cover plate on an electrical outlet). Speaking of resistance:

5. When measuring resistance, it's a good idea to disconnect one end of the resistor. Otherwise, your readings will be affected by other resistors in the same circuit. Resistors in series (one end connected to another end) will add together, while resistors in parallel (one across another) will measure lower than the highest-value resistor (it's complicated). Best to just unsolder one end of the resistor being tested, and test it that way.

Hope this helps.
-Adam