Probably a stupid remark but, wouldn't it be possible to shield the inverter if it causes interferences?

Aha, this is very helpful! Thanks!

Values are the same as native (they're written on the caps) I replaced them just in case. I'm not sure about pro sound since this was a gaming gameboy.

If you want to avoid hum I suggest using this approach http://chipmusic.org/forums/topic/6031/ … -mount-ic/

In one of my other projects I used DIP inverter, but managed to allocate it right above the LCD jack and in such position there's no hum at all. If you're using ThursdayCustoms's biversion kit you're fine as well

The hum appears when your inverter is somewhere in the region of GB processor on the link port half of the board. That's what trial and error shows.

I will probably do this mod in a near future, would you mind telling which cap did you replace and with which value?

Also, does this hum issue concerns only the regular mini jack output or also Pro mod sound output as well?

Thanks!

Today I biverted one of my old backlit DMGs and discovered that it indeed produced hum. What I did is opened the case and started moving the hex inverter around (I used a SOIC package so I had it wired and thus was able to relocate it while GB was on). I discovered two things:
1) it's better not to take power from the power regulator pins instead I powered it from a +5V above LCD connector. when i did that the amount of hum decreased significantly
2) when the inverter is located on the side with the power outlet there's almost no hum and vice versa - move it to the side with the link port and your hum will turn into a hypnotoad

Apart from the aforementioned points I also replaced a cap on the power regulator with new (and bigger) one and replaced both caps on the phone jack PCB. And I have no hum at all.

Of course it was a 'mechanical' solution. I don't know the real cause of the hum and so have no clue how to address it by the book.

You might try adding a bypass capacitor to the power supply pins of the inverter. Basically because it's digital, every time the logic level switches it changes the load on the power rail and that adds electrical noise to the whole thing. This will certainly show up in the audio if it's at the right frequency. The cap acts as kind of an electricity reservoir so quick little bursts get taken care of by that instead of the whole system.

I wouldn't have minded if it were a nice hum, but it was a high-pitched whine.  I ended up swapping the LCD board with another one instead of bridging and grounding the biversion chip.  This one is so much quieter.

Hmm. Yeah. I noticed a hum too. So far only installed two successful backlight mods but one of them has a clearly louder hum emitting from the internal speaker.
Not that that really matters, it just purrs like a little machine kitten.

I could only expect that it's a little like what happens to computers where there this thing: like if you have a sound cable thingy hanging too close a graphics card or something pressure on the graphics card can actually be heard through speakers or headphones. Very common "problem". ???

I have this issue with one of my DMGs.  all I've done to this one is change the caps, put in a half CLK, and a white backlight and prosound.

Not sure if the hum appeared after I did the mods or was already there. I couldn't figure out what it was that did it but I did notice it's only in one of the jacks.

It does, but maybe they want to play other stuff inverted or whatever.

But doesn't LSDJ have a invert option built in now?

yea, really all you need to ground is the output pins. you could ground ( and bridge), all of the pins not in use

It's a good idea.  Could I ground the unused pins by bridging them and just grounding the bridge, instead of running a separate wire from ground to each leg? I'm going to hold off for a bit to see if anyone else has any experience with this exact issue, but if not I'll probably try opening it up again and grounding.

That's not what's supposed to happen.

Edit: From my limited knowledge on the subject, this sounds reasonable. I know I always get extra whine and hum with my guitar gear when there's a grounding issue.

more contrast for more hum doesn't seem like a good trade off.