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Dreamcast VA0: Lowering voltage for GDEMU?

lanocy99

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Hello, first time poster here.

I have a Japanese VA0 Dreamcast which I'm aware that it is not compatible with GDEMU. Most people familiar with GDEMU know that although it's physically compatible with both VA0 and VA1 revisions, it's designed to receive 3.3V which only the VA1 correctly provides.

I have recently spotted a Reddit post (and its corresponding YouTube video) where the user installed a clone GDEMU without realising that it's a VA0 console. I've cross-checked my Dreamcast with the one shown in the video it is definitely a VA0 revision based on the matching hole patterns on the metal shield and controller board part number. It seems to be working fine and performs as expected.

A friend who I asked as well as Deunan on the GDEMU site notes that although it will appear to work fine in a VA0, the 5V supply will generate more heat than usual and inevitably damage the module/console in the long run. I know that I am ignoring the obvious warnings already and I'm not overly familiar with electrical stuff to begin with (I'm fine with some soldering though), but I wonder if it would be possible to install some type of resistor someplace in the console to lower the GDROM supply to 3.3V? What would this entail?

Thanks!
 

bbccoon

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Hi all,

Sorry to dig up this post, but @megavolt85, I noticed you posted the reference for a TI chip that it looks like it can do the work of converting 3.3v to 5v and vice-versa. Can you elaborate on that a bit more? Do you see any workaround using that chip?

Thanks in advance
 

Trimesh

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Unfortunately, what you are trying to do is not trivial - the G1 bus that the GD-ROM drive connects to is bidirectional so you also need to generate the correct signals to turn the transceiver around depending on the direction of data flow at any given period of time.

Also note that the G1 bus has always used 3.3V signalling levels - it's just that the original Holly chip used in the VA0 consoles was 5V tolerant and the boot ROM and the on-board flash (which are also on the G1 bus) ran from 5V. The result of this is that although the actual data transfer between a VA0 Holly chip and the GDEMU will work fine the bus interface on the GDEMU may be exposed to out-of-spec voltages during bus cycles that read from the boot ROM or the on-board flash.

Honestly, my suggestion would be to find a VA1 console - they are more common and run cooler anyway.

(Changed VA0 to VA1, since my brain was clearly in standby)
 
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Ergot

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All the superior knowledge that your brain holds has pushed out the simple everyday knowledge.
 

bbccoon

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Thank you for your reply @Trimesh.

I really wonder if this is a problem that no one bothered to solve because percentage of VA0 systems is low or if it is actually a hard problem. Often non trivial problem have simple answers once they are found, but it could also not be the case here. Is there any source for the GDEMU components and operation method? On the Dreamcast, I found this text.

Personally, I think that the VA0 are lovely systems (with its metal parts on heat dissipation system, sexy) and the build quality to me always seemed superior. The GDEMU is a great step for preservation, but there is still, from my understanding, no solution for storing all the Dreamcast library in one system (I believe I did read about SD card size limitation on GDEMU). HDD mods are also unappealing not only because hard drives have quite limited life span and there is no 100% compatibility as GDEMU.

Thank you by your answers, wishes of a great week.
 

Trimesh

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No, it's not a hard problem at all - you just need to either use translation voltage clamps or 5V tolerant parts interfacing to the data bus. The latter is the reason that the USBDGROM works on VA0 systems - it's using the same Toshiba interface chip that the original GDROM drive used, and that's 5V tolerant.

Although I do like the heatpipes, my main issue with the VA0 is that the Holly chip is made on a larger process and hence takes more power and runs hotter.
 

Tokimemofan

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Thank you for your reply @Trimesh.

I really wonder if this is a problem that no one bothered to solve because percentage of VA0 systems is low or if it is actually a hard problem. Often non trivial problem have simple answers once they are found, but it could also not be the case here. Is there any source for the GDEMU components and operation method? On the Dreamcast, I found this text.

Personally, I think that the VA0 are lovely systems (with its metal parts on heat dissipation system, sexy) and the build quality to me always seemed superior. The GDEMU is a great step for preservation, but there is still, from my understanding, no solution for storing all the Dreamcast library in one system (I believe I did read about SD card size limitation on GDEMU). HDD mods are also unappealing not only because hard drives have quite limited life span and there is no 100% compatibility as GDEMU.

Thank you by your answers, wishes of a great week.
Probably just due to the rarity of va0 units. I have only seen 3 us va0s in my time collecting out of at least 100. Va2 is not common either. At least 90% of the us production seems to be VA1
 

FamilyGuy

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I really wonder if this is a problem that no one bothered to solve because percentage of VA0 systems is low or if it is actually a hard problem. Often non trivial problem have simple answers once they are found, but it could also not be the case here. Is there any source for the GDEMU components and operation method?
I think it has more to do with the fact that a Dreamcast is worth less than a GDEmu at this point. There's a diminishing return in that feature.

So if you only have a V0 and want a GDEmu, why not just get a VA1 for like 20$?
 

Tokimemofan

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I think it has more to do with the fact that a Dreamcast is worth less than a GDEmu at this point. There's a diminishing return in that feature.

So if you only have a V0 and want a GDEmu, why not just get a VA1 for like 20$?
Or even better call you local retro game shops, see if they have a broken one they would sell for cheap, probably a bad laser or a minor quick fix fault.
 

bbccoon

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not only Dreamcast are extremely hard to come across where I am located, getting one from ebay it is an overpriced solution.

the console I grew with was a PAL VA0, the one I got last weekend by a bargain is NTSC-J VA0 (I moved to a new country, PAL VA0 is in my hometown). No one here is questioning how hard or not is to come by a VA1, I am not actively looking for one even because I have original copies of mostly everything I want to play. I am just curious :)

Thanks!
 

truemaster

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you can just replace the motherboard with a va1. ebay has just the motherboard
 

FamilyGuy

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you can just replace the motherboard with a va1. ebay has just the motherboard
You might need a different controller PCB too, IIRC they don't have the same amount of pins because of the different fans.

If you get a va1 and the controller port doesn't fit, just tell me I have a few spare ones.
 
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