7900GT Voltmod-2

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05-02-2006, 12:04 AM
alpha0ne

Quote:

Originally Posted by flytek

thanks for finding that pic graham. i've been wondering what has happened to the new pcb. it looks like they ruined the nice digital vgpu mod.

Yes they have :slapass:
05-02-2006, 12:07 AM
C-BuZz

card is officially dead ;(

replaced both mosfet's & tried to boot & the same mosfet went up in flames. When I mean flames, it burst into flames & melted my solder joints & fell onto my motherboard :eek: Was burning for about 5seconds with a nice yellow flame..

Nothing else was damaged luckily.

C-BuZz
05-02-2006, 12:30 AM
alpha0ne

Sorry to hear though you maybe could have made a fortune selling the video of the fireworks :eek: :D
05-02-2006, 12:35 AM
C-BuZz

Quote:

Originally Posted by alpha0ne

Sorry to hear though you maybe could have made a fortune selling the video of the fireworks :eek: :D

heh, can always solder another in its place :)

C-BuZz
05-02-2006, 12:53 AM
s e t h

@graham - did you take that picture? maybe you could get the full codes of the largish elongated chip about an inch below the 0605 date stamp. that'll be the vgpu controller i would think.

the two 8 legged ones at the below that chip will probably be for the vmem. full codes would help there too.

thanks
05-02-2006, 12:55 AM
graham_h

flytek it is my card I'll try and get some more with a bit more detail
05-02-2006, 01:00 AM
s e t h

exellent. also it would be very interesting to find out what coolbit's nvidia driver autodetects the core/mem frequency overclock at.
something else of great interest would be stock frequecy clocks and a 3dmark06 run.
lastly the codes of one of the ram chips would be very nice to know. for all we know gainward changed that on these golden samples
05-02-2006, 01:26 AM
graham_h

Stock

http://img235.imageshack.us/img235/1...06stock9mm.jpg

580 core

http://img69.imageshack.us/img69/9176/3d065807005pi.jpg
05-02-2006, 01:40 AM
t024484

Quote:

Originally Posted by C-BuZz

card is officially dead ;(

replaced both mosfet's & tried to boot & the same mosfet went up in flames. When I mean flames, it burst into flames & melted my solder joints & fell onto my motherboard :eek: Was burning for about 5seconds with a nice yellow flame..

Nothing else was damaged luckily.

C-BuZz

Sorry to hear.
To find the reason is not easy, but for a mosfet to explode into flames, probably means that it was not fully turned on while transferring lots of current and because of that is dissipating huge amounts of heat.
The device responsible for controling this mosfet is the voltage regulator, so my guess is that your voltage regulator is no longer working properly.
Replacing this device is beyond the scope of a hobbyist, but chances are high that your memory also received a voltage that was too high and is damaged because of this.
You could try to test the board with an external power source (with both mosfets removed) to find out if it is worth investing any further.
05-02-2006, 01:47 AM
C-BuZz

Quote:

Originally Posted by t024484

Sorry to hear.
To find the reason is not easy, but for a mosfet to explode into flames, probably means that it was not fully turned on while transferring lots of current and because of that is dissipating huge amounts of heat.
The device responsible for controling this mosfet is the voltage regulator, so my guess is that your voltage regulator is no longer working properly.
Replacing this device is beyond the scope of a hobbyist, but chances are high that your memory also received a voltage that was too high and is damaged because of this.
You could try to test the board with an external power source (with both mosfets removed) to find out if it is worth investing any further.

how would I power the card with an external source?

Im just guessing, but I dont think that the current flowing through the mosfet is supposed to be so high? Would have to be at least 12v to do damage like that? The chip it totally unrecognisable & basically turned to powder.

C-BuZz
05-02-2006, 02:07 AM
t024484

Quote:

Originally Posted by sluggo

When you reduce Rds in a mosfet you typically increase the Qg, or total gate charge. That's the case here, as the Infineon part has 3x the Qg of the IR part, and a corresponding increase in the turn-off delay. Dumping the increased gate charge 250k times per second leads to dramatically increased switching losses. Idle temperatures for the Infineon part will be significantly higher. Given that MSI is using it, though, it's certainly okay at stock switching frequencies.

If you increase the switching frequency of the FET, however, switching losses increase linearly. An Infineon part with the frequency mod described here will have switching losses around 6x the IR part at stock switching frequencies. If the IR part is fairly hot at idle, the Infineon part will be very hot when overclocked.

My point is that overclocking the Infineon part will not necessarily be easier or even possible.

Sluggo, your information is both wrong and misleading.
Wrong because the 32n03 has a total gate charge that is only half the gate charge of the 4420 that it replaced, wrong because a turn-off delay does not generate heat, and wrong again because the Infineon turn-off time is in fact shorter than the IR part.
Misleading because charging and discharging a capacitor does not generate any heat in that capacitor (or Mosfet), apart from the (mostly neglectable) loss factor.
And as a last remark, the switching frequency for Vmem is 660Khz and not 250Khz, and has never been overclocked by anyone as far as I now of.
05-02-2006, 02:09 AM
s e t h

you mean the main vpgu voltage regulator t024484? maybe the vgpu mods are staining the vreg in the wrong way and leading to the vmem mosfets burning out?
05-02-2006, 02:13 AM
xit

Quote:

Originally Posted by C-BuZz

card is officially dead ;(

replaced both mosfet's & tried to boot & the same mosfet went up in flames. When I mean flames, it burst into flames & melted my solder joints & fell onto my motherboard :eek: Was burning for about 5seconds with a nice yellow flame..

Nothing else was damaged luckily.

C-BuZz

Nasty. Did you remove all mods including the pencil rub first?

You could always *try* to RA it and say "it just blew up!" lol
05-02-2006, 02:21 AM
t024484

Quote:

Originally Posted by C-BuZz

how would I power the card with an external source?

Im just guessing, but I dont think that the current flowing through the mosfet is supposed to be so high? Would have to be at least 12v to do damage like that? The chip it totally unrecognisable & basically turned to powder.

C-BuZz

The mosfet that is burnt out is connected to the 12Volt, and your memory needs just 2 Volt. Suppose that 10Amp is flowing with a Drain to Source resistance of 1 Ohm, this will generate 100Watt, more than enough to blow your Mosfet to pieces.

What you need is an external power source capable of supplying 2Volt and preferably something between 15 and 20 Amp, and of course with a good short circuit protection. If you cannot borrow this somewhere, there are companies specialised in renting such electronic equipment.
05-02-2006, 02:27 AM
t024484

Quote:

Originally Posted by flytek

you mean the main vpgu voltage regulator t024484? maybe the vgpu mods are staining the vreg in the wrong way and leading to the vmem mosfets burning out?

No I am talking about the 6549 Voltage regulator for Vmem.
This one works completely independant and is not influenced in any way by the 6568 voltage regulator for Vgpu.
05-02-2006, 02:38 AM
s e t h

it's a real pleasure to have you on the board t024484 ;)
05-02-2006, 03:29 AM
xit

Quote:

Originally Posted by flytek

it's a real pleasure to have you on the board t024484 ;)

He is a bit of a legend. Is that a crocodile embryo as your image? Or a Jurassic Park promo pic? :slap:
05-02-2006, 03:54 AM
t024484

Quote:

Originally Posted by xit

He is a bit of a legend. Is that a crocodile embryo as your image? Or a Jurassic Park promo pic? :slap:

Nail on the head. It is a Croco embryo.
05-02-2006, 03:56 AM
xit

Quote:

Originally Posted by t024484

Hit on the nail. It is a Croco embryo.

Thought so....damn they're tasty. :stick:

Anywho, back to the 7900's !!
05-02-2006, 07:07 AM
sluggo

Quote:

Originally Posted by t024484

Sluggo, your information is both wrong and misleading.
Wrong because the 32n03 has a total gate charge that is only half the gate charge of the 4420 that it replaced, wrong because a turn-off delay does not generate heat, and wrong again because the Infineon turn-off time is in fact shorter than the IR part.
Misleading because charging and discharging a capacitor does not generate any heat in that capacitor (or Mosfet), apart from the (mostly neglectable) loss factor.
And as a last remark, the switching frequency for Vmem is 660Khz and not 250Khz, and has never been overclocked by anyone as far as I now of.

I wasn't comparing the 32n03 to the 4420, I was comparing it to the IRF7821. The guy with the burnt chip was considering replacements for his fried 4420 and I was advising him on the pros and cons of the those two alternatives.

I didn't say or imply that turn-off delay created heat. I mentioned it only as an illustrative consequence of the higher gate charge.

Discharging a capacitor most certainly does generate heat. A current has to remove the charge, and that current has to pass through a conductor with some finite resistance.

My mistake on the frequency, the Vgpu switches operate around 250kHz and that number stuck.
05-02-2006, 08:14 AM
t024484

Quote:

Originally Posted by graham_h

Stock 550/700 3DMark06 score 5244
580/700 3DMark06 score 5411

graham_h,
You certainly bought the 7900T/512 because you were looking for an improved performance.
Do you already have comparable results between the 7900GT and this new board, both with the same clock speeds.
That would be great to see.
05-02-2006, 08:15 AM
revenant

Where are you guys getting your GW GTs from?
05-02-2006, 08:34 AM
timchen

Hi guys, nice discussions here!!

Hello guys,

I've roughly read through this lenthy discussions. Nice mod really!
I had a card vmod 1.4v, no vmem mods.
640/900... not a big overclocker but I am satisfied with it. :)

My question is about those MOSFETs.
In my case, they got extremely hot. Though the computer is quite stable even without heatsinks, I dare not put them.
After putting them on, the heatsinks still measure ~70 degrees celcius or up (well, with my fingertips... maybe not very accurate...)

so I managed to put a fan to blow some air onto the chip and the heatsink, and then... my motherboard temperature goes up about 5 degrees!!

How hot actually are those chips?
I am starting to think it is after all not a very stable mod...

I am curious about their functionality. Why are the two switching to each other? What do they actually do?
05-02-2006, 09:06 AM
t024484

Quote:

Originally Posted by timchen

Hello guys,

I've roughly read through this lenthy discussions. Nice mod really!
I had a card vmod 1.4v, no vmem mods.
640/900... not a big overclocker but I am satisfied with it. :)

My question is about those MOSFETs.
In my case, they got extremely hot. Though the computer is quite stable even without heatsinks, I dare not put them.
After putting them on, the heatsinks still measure ~70 degrees celcius or up (well, with my fingertips... maybe not very accurate...)

so I managed to put a fan to blow some air onto the chip and the heatsink, and then... my motherboard temperature goes up about 5 degrees!!

How hot actually are those chips?
I am starting to think it is after all not a very stable mod...

I am curious about their functionality. Why are the two switching to each other? What do they actually do?

One chip is the voltage regulator for the memory voltage and the other one is a Mosfet connected to this regulator.
Together with a third Mosfet they form a "switching regulator" to make 2Volt out of 12Volt with a relatively high conversion efficienty.
So the Vgpu modding you have done has no impact on the heat development of these components, but of course the memory overclocking to 900 has. Going from 650 to 900 let the current increase accordingly.
A heatsink is very good, and 60-70 degrees seems O.K.
The ventilator you are using is probably directing its flow to the measuring diode on your motherboard, thats why.
05-02-2006, 09:16 AM
C-BuZz

Quote:

Originally Posted by t024484

The mosfet that is burnt out is connected to the 12Volt, and your memory needs just 2 Volt. Suppose that 10Amp is flowing with a Drain to Source resistance of 1 Ohm, this will generate 100Watt, more than enough to blow your Mosfet to pieces.

What you need is an external power source capable of supplying 2Volt and preferably something between 15 and 20 Amp, and of course with a good short circuit protection. If you cannot borrow this somewhere, there are companies specialised in renting such electronic equipment.

Where/how would I connect such a power supply to my board with no mosfets?

Quote:

Originally Posted by flytek

it's a real pleasure to have you on the board t024484 ;)

I concur :toast:

C-BuZz

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