Replacing the DC PSU

I have no idea which one is mine but I used to use it with a consolized NeoGeo, which had a 5v 3a brick. Than maybe I can use 9V and skip 12v entirely.

 

The model should be written on it somewhere. Typically the yellow connector ones are 12v and the red are variable.

But maybe the 12v ones simply don't regulate the input, so 9v might not be harmful as long as you leave the 12v output disconnected. The pico might be less efficient than designed in this case.

 

Got this figured out. http://assemblergames.com/l/threads/usb-gdrom-thread.56946/page-7#post-823439

 

Hi

I wonder if anyone can help me? I am trying to get my (PAL) DC running from a PicoPsu. I have been successful in replacing the stock PSU with a PicoPsu, my dreamcast powers up and games play fine but the RGB picture output has suffered dramatically. Picture seems noticeably softer and there are bands of horizontal dots running diagonally across the screen (if you can make sense of that?) it is not so noticeable on a colourful game like crazy taxi, but Rez, my favourite game, looks awful as the dots are very apparent on the black background. It works fine with stock PSU.

It is a PAL DC bios flashed to Europe/ntsc/english, GDEmu v5.4, RGB scart, Same results on a PicoPsu 90 & 120 both using the same 12v 5a power brick.

 

It sounds like the dreamcast isn't outputting enough current on the 5v line for the vga mod. The V-sync and H-sync are pulled up to 5v by the mod which could explain why the image is now blurry and containing artefacts. Get a multimeter and test the voltage and current on 5v (AV port) with the old psu and then the pico psu attached. Compare any differences.

 

Thanks for the advice.

haven't done a vga mod, I am just using rgb scart lead straight out of regular av port.

It sounds like you know what your talking about so I better get a new battery for my MM and check that. For now I have gone back to stock PSU and added a heatsink and 12 volt fan to motherboard cover plate, this has certainly brought the temperature back to normal but added more noise!

 

Sounds like interference from the Picopsu :/ I don't get any such issues but mine is not close to the AV port.

 

My mistake, I thought u were running a vga mod. I'm not an expert on the subject I just learn from the amazing modders I meet on this forum and others. If the pico works for other peopl then it is more likely as Rocky5 says, interference. But a multimeter test won't hurt.

 

The picoPSU is much overpowered for the DC, so the issue is most likely not it.

Let me make a wild guess here, you put the picoPSU near the back of the console close to the AC plug hole? If so, it's probably interference caused by the switching in the PSU, which is typically near the tens of kHz, just like the vga signals. Try to put the picoPSU further from there and you should be fine.

If it's not the problem, I don't know what can cause this.

 

I have the same problem with all 4 PicoPSUs I bought. Diagnonal lines of crap running across the screen. This ONLY happens on 3rd party Scart cables though. I have one original DreamCast Scart cable and the picture is perfectly fine with it.
Location of the PicoPSU have no effect. I moved it 40cm from the dreamcast when I tested one and still the same thing. I also tried encasing the pico in a metal box with no difference.

 

try using different power brick

 

Turranius, where did you get the plate for mounting the DC female power jack socket? Looks a nice fit. I was thinking of fabricating something like that if I couldn't find one on the internet or cannibalise it from something...

Ted.

 

Looks like a piece of tin, hole drilled, cut and bent to me.

 

Its actually a bit of shielding from the top of an Amiga motherboard that I folded and cut by hand and eye measurement. I also found a sheet of metal I had laying around that I used later. I used some old scissors to cut it to size and just bent it with a piece of pliers. Easy.
Drilling the hole was quite hard though. I learned not to drill the hole before I start cutting into it too much. The hole needs to be nearly the size of the visible section and I ended up ruining it a few times..

 

I have tried the PicoPSU in multiple positions. No improvement in problem. I also tried 'shielding' the PSU with some foil, no difference.

I too am using a 3rd party RGB Scart cable, so I guess that is the problem. I wonder why that is? It seems a pretty good cable, clean signal and no interference normally. I have had some really poor RGB scarts for other systems and their problems have been obvious straight away.

 

Sounds like the PicoPSU is noisy, maybe someone with an oscilloscope can take a look at the 5V and 12V lines. Or just create a loop between ground and center pin on the test probe. Then use this "wand" around the Pico PSU and the 12V supply. Might be an idea to use the "wand" around the original PSU as well.

If your system works/worked fine with the original PSU and RGB cable the PicoPSU is too blame.

 

I don't think it's a fault with picopsu as I have tried 2 now, and Turranius tried 4 different ones. I guess the official Scart just has better circuitry to deal with the noise. What would help would be for someone more knowledgeable than myself, who has both 3rd party and original scart leads, to compare the 2 leads internally and see what is different.

I am watching a couple of official leads on the bay, when I get one I will attempt to compare them.

I am in no hurry though as I have added a fan to the 12v line from original psu and that has sorted the GDEMU heat issue perfectly, in fact I think it runs cooler than it did with stock psu and GDRom installed, and it is still quieter than it was when reading disks.

 

Dumb question:

When connecting the dreamcast power switch to PS_ON & ground (on the picopsu) , does the polarity matter? I see a capacitor stuck on the switch but i assume it's not polarized so it doesn't matter...

 

The cap is non-polar and a switch has no polarity, it either acts as a wire or as a non-wire.

The short answer is thus "no".

 

Could someone please link a power supply that would be good for the pico psu thats in the UK (ebay preferably).
I've ordered the psu but am not 100% sure on what power supply will fit it properly.