USB GDrom Thread

^ agreed, picoPSU is the way to go unfortunately

 

you need 3 parallel resistors from 120-180 ohms @ 5-6 watt

13.10 V is good but the resistor will over heat and as you said you need to produce some load, from my measurements 0.06 A is the load of the gdrom without disc inside and 0.17 A is the average and 0.25-0.30 A on disc seek. Also i measured the voltage and the minimum i get is 12.65V from the original dreamcast psu on disc seek.

so 40-60 ohms resisstance is good but at that voltage the resistors will overheat and to fix that you need 3 parallel resistors from 120-180 ohms

correct me if i am wrong [ima noob at electronics]

 

Resistors also have a wattage rating. You just need a large enough resistor to handle the wattage. You could do three parallel , or buy one higher watt rated resistor.

So say 14 V times .5 Amps to be safe is a 7 watt resistor. For .3 amps that would be like 4-5 Watts.

Here is a 300 Ohm 12 Watt resistor.

http://theelectrostore.com/shopsite_sc/store/html/hlw-12-a1z-300ohm-dale-new.html

They also have a 5 W one but they may or may not be enough.

There is a formula to determine what value of resistor you need as well. But you would also need the power supply resistance to calculate the right size resistor. Best just to find a resistor value that brings down the voltage. Multiply the voltage times the amperage to get a wattage.

 

yes i forgot to mention this... P=I*V but i tested a 120 omh ceramic resistor at 6w and the temperature is not good so 3x120 omh resistor at 5-6 watt parallel will do the job as i tested, i see there are a lot of resistors types and i don't know the thermal behavior of all

edit: 3x120 omh resistor at 5-6 watt parallel (40 omh)

 

This is pretty much the same and should work, correct? The resistor I have helps but would like to further reduce the output voltage.

http://www.mouser.com/ProductDetail/Ohmite/B12J300E/?qs=4Pfac2pIcodItvRcKfeWQA==

 

When resistors are in parallel there omh value drops. 6 x 120 ohm resistors in parallel = 20 ohm

I just said the hell with it and ordered a 300 ohm 20watt resistor. Its 2" long so should be fun stuffing it in.

 

shit 3x120 sorry again, the drive have about 30-200 ohm resistance and 50 ohm on disc seek use so 3x120 is 40 ohm

 

Well I just picked up that 300 ohm resistor. I will test it out and see how hot it gets and what the voltage is. Need to find my infrared thermometer now, garage is a disaster at the moment :-(

 

I would just use what people have found already works to be honest. A 20 watt resistor seems like overkill. But it's probrably cheap so I guess it doesn't hurt. Wasn't wasn't there another thread on pico power supplies that said someone removed the 12v circuit from the power supply entirely? And it worked fine. Appently it was theorized only the GD Rom used the 12V. And it's confirmed the USB-GD Rom card does not use 12V. But what components to take off to remove the 12V is something I can't answer right now. Once I get my card and verify everything working I may try that.

 

Yeah the resistor was only like 4 bucks. I'd much rather remove the 12 volt all together. That would remove any extra heat. Where did you read about that?

 

It's in this thread.

http://assemblergames.com/l/threads/replacing-the-dc-psu.53856/page-9#post-811637

 

Yeah, I am a cheap bastard as $214 from SAG is way too rich for my tastes. I hope cybdyn still makes his version. I want the USB Gdrom for the ability to use USB devices up to 2tb, but I prefer the price of the GDEmu a lot more than the UGC.

I really hope he gets that device finished and marketed because many people would prefer a much more affordable device. Not everybody can shell out $200+ so easily.

Anyways this is still the early days and there is only 1 other alternative than that is the IDE HDD mod, which isn't as compatible as these devices are.

 

Thanks I will try this out tonight.

I successfully removed the 12volt from the psu. Still doing some further testing but crazy taxi has been going for over 4 hours now. I'm going to let it run over night and see how she fairs. Circled in white are the two components you need to remove. The surface mount resistor and the transistor.

Edit: So I've let my dreamcast run for over 16 hours everything is still purring along just fine. I'll give some more updates the more I use it.

 

My PS is a different revision but the transistor is in the same spot. It has a different name. I just followed the 12v pin back and 12 V regulator seems the same across revisions. Just different names. I was thinking pull the 3 pin transistor and the resistor next to it the same as you did. At least now I know someone did it. How is the heat?

 

Aw, man. I thought I solved the issue with the resistor recommended in that video. I guess not.

 

ive used then machine a few time since and havnt had any issues. heat seems less then normal.

 

Citrus, was what you did difficult? I'm not a modder at all, it sounds like your solution may be ideal but I'd hatw to screw it up.

 

My DC PSU is exactly like the photo. I was going to install the Pico PSU but removing the transistor and the resistor are way easier.
It's working flawlessly here.


What kind of image files are you guys using? I have the tosec set but it's huge for a thunb stick. Is there a way to reduce the image sizes without going too much into hacking and hex editing?
1.2GB takes too much space.

I believe familyguy posted a set of tools to do it, did you guys had any success with it?

 

It's Rocky5 that made the scripts, he used tools from S4phar4d and myself.

AFAIK it's not compatible with the USB GDrom right now, but GDEMU handles it fine.

It's perfectly possible for mnemo to support those "Fat-Trimmed" images in the future, everything should be fine as long as the DC doesn't try to read in the cropped areas, but since nothing points there, it shouldn't be an issue.

 

You are always fast to trigger a reply!

I'll try talk to him about this, I think he's not even aware of this since he made his device to support up to 2TB.