Question Making a really strange sound...?

[HapticNoise]

Hey all, first time poster here. After spending lots of time lurking modretro (RIP) and watching lots of people’s YouTube videos of their projects, I decided to try something on my own console. It was kind of sitting around collecting dust and I had been looking for a neat hobby. So several months, one sketchy trim job, several Amazon orders, and untold yards of wasted solder later, here we are. Unfortunately I had to find a lot out by trial and error because of modretro’s inactivity, and I didn’t see any link to these forums until I happenedupon one in a modretro thread yesterday. I imagine I could’ve saved myself several headaches if I had known about this place beforehand, but oh well!

I won’t go into detail with the specifics of the project here because that doesn’t pertain to my immediate question. My immediate question is this: when powered up and hooked up to my CRT (I’m actually running this off of wall power and using a CRT — just recasing everything to look nice and neat), nothing happens, and then this rhythmic popping noise starts coming from the speakers of the TV. I took a video of the noise, link here:
When putting my multimeter to it, voltage on both the 12v and 3.3v lines drops in time with the popping noises, and you can see in the video how the picture on the TV reacts. Obviously there’s some kind of buildup and release going on, but I have NO idea where to start looking and what to start testing. I know I haven’t provided a wealth of information on the specifics of my particular project, but I was hoping that someone may know immediately what the issue is without that. Any help would be phenomenal, thanks a lot in advance everyone! Looking forward to spending lots of time here

 

[cheese]

Take a look at your regulators. Since the voltage is dropping, that would probably be causing the system to restart/crash every time there's a voltage drop. Honestly, we can't say much since we don't have anything to go on...
Did you trim your console, use custom regulators (if so, which ones), do you have a game in, do you have a expansion/jumper pack inserted or hooked up, did you accidentally short something at some point?

Taking a picture of your board as it is hooked up in the video would be the fastest way, since we can look for many common mistakes

 

[HapticNoise]

Sure. It’s all kind of a mess right now, but here it is. If you need a clearer picture of anything let me know. The only things on the back are the red wire going to the 3.3v trace and 3 small wires for controller connectivity, disconnected at the moment

 

[Madmorda]

How many amps is your power supply giving it/ how many does it need? I found that if my gcp wasn't getting enough current it would do something similar to popping.

Edit: also, did you sand the edges of your board really well after trimming? If you didn't, the edges could be shorting something.

 

[HapticNoise]

The power supply is from an Asus laptop, rated at 19VDC/3A, and I step it down to 12V before sending half to the console and half to another converter to go down to 3.3V.

No, I honestly didn’t sand anything. I didn’t really think it would be an issue with how conservative a trim it is, but I can definitely give it a go if you think it would help

 

[MasterNate]

Sanding is one of the main problems when trimming a board. Sanding is necessary, not optional, when trimming a board.

 

[Bakuku]

Sanding is one of the main problems when trimming a board. Sanding is necessary, not optional, when trimming a board.

This is probably one of the most important rules you need to adhere to!

 

[HapticNoise]

Okay, thanks guys! I’ll give it a go, what grits are best when sanding? I know I have some 80 grit laying around, not sure what I have in the finer grits, I’m not home atm

 

[MasterNate]

You want to start with low grit and work your way to higher grit. Work your way up to 500-600 grit in about 20-30 grit increments. After you hit 500-600, you should be all set.

 

[HapticNoise]

Okay great, thanks! Will report back

 

[HapticNoise]

Also, is it necessary to sand down the grounding strips as well? There’s kind of a lot of hot glue on the left hand side from where I might have adhered it to the new case before properly testing anything

 

[MasterNate]

Just sand down any edge you cut.

 

[HapticNoise]

Well. I found it. I don’t know how I managed to miss this the entire time. So should I just cut off the U8, or what? Pretty sure I’ve read somewhere that that’s possible if you just bridge certain pins on the PIF. What do?

I don’t remember what rev this is exactly, it’s been a while since I’ve cut the top of the board. It’s definitely a later rev though. Not sure if that changes anything with the U8/PIF

 

[Stitches]

You could use some 30-38 gauge magnet wire, scratch the mask off the trace a bit further up from the swoosh, and solder a small wire from the U8 leg to the scratched trace. That'd restore functionality, assuming it's the only problem. You'll just have to cut the trace just above the swoosh, it looks like it's bridged to the ground plane.