BF6 Mosfets

[Smiffy]

Hi All
Just picked up a BF6 with a few blown caps.There are 2 mosfets marked as 76129S next to the ATX connector and I cant find any datasheets for them.They are getting hot with a Tualatin 1.3 so I would like to upgrade them.Does anyone have any info about them?.Many thanks for any help.
Smiffy

[Rainbow]

Re: BF6 Mosfets

[davmax]

Re: BF6 Mosfets

The previous link malfunctions. Try this one: http://www.ortodoxism.ro/datasheets/...HUF76129P3.pdf

The MOSFET is a powerful device at 56A 30V. It might be an idea to find out why they are getting hot. Most mother boards have several sharing the Vcore load ie two or three phase convertor.

Can you show a pic of board and MOSFETs?

[davmax]

Re: BF6 Mosfets

The MOSFET on your board is apparently obsolete. So if you need a replacement that is better go here for data: http://www.st.com/stonline/products/...00nf03l-03.pdf

This MOSFET is characterised to be fully ON with a 5 Volt logic input that the original required. It has lower ON resistance and rated at 100A.

It appears that the manufacturer sells off web page here :
http://www.st.com/stonline/stappl/pr...TC+0800%202006

[davmax]

Re: BF6 Mosfets

On further inspection the replacement suggested is not so good for high speed converter such as VRM. The switching speeds are substantally slower. Current rating is just one factor.So will need a better alternate. I suspect that as current rating rises the switching speed slows.

I will take a wider look for you.

[davmax]

Re: BF6 Mosfets

This device is faster

http://www.st.com/stonline/products/...tb200nf04l.pdf

The following Fairchild device looks designed for this application but the turn off times are poorly specified ( at 1 amp only for an 80 amp device) additional the ON resistance is higher.

http://www.fairchildsemi.com/ds/FD%2FFDB7030L.pdf

On balance the ST device looks better and probably more obtainable from manufacturer.

About as far as I will go at this stage.

[davmax]

Re: BF6 Mosfets

Here we go again!!! The challenge when upgrading to a higher current MOSFET is that the input capacitance increases. Too much increase will slow down the switching speed as the driver chip stuggles to charge and discharge the input capacitance. This will increase switching losses and increase heat. In some cases this may damage the driver chip.

Take the last two replacement possibilities.
1. Fairchild FDB7030L input C = 2440pf
2. STB200 input C = 6400pf.

The original 76129S input C = 1350pf

From these figures it would be reasonable to use the FDB7030L as a replacement but the STB200 is pushing input C too high.

It has been fun searching this out. Hope this helps.

I re-emphasise that you try to find out why the MOSFETs are getting hot before replacing.

[PeteS in CA]

Re: BF6 Mosfets

Another thing to look out for on some MOSFET datasheets is that some vendors give the continuous current rating of the die, but the true rating is limited by the package - TO-220 and D2PAK are typically 75A or 80A, though STMicro has some parts that are package-limited to 90A or 100A.

High gate capacitance (or gate charge) can cause problems two ways. If the driver can't handle it, turn on and turn off can be slowed and the driver may get hot. If the driver can handle it, this still uses extra power to drive the gate.

[davmax]

Re: BF6 Mosfets

True Pete. The STB200 is rated for 120 Amps @ 100C case temp, that is very good and determined mainly by the very low ON resistance.

I guess in the Smiffy case if there is no increase in load we will get lower heat generated in a lower ON resistance device as long as the switching losses are kept down. It seems the main issues are:
1. Is any increased loading causing a temp rise? Like faulty caps.
2. Is there anything preventing the heat from being dissipated? Like insufficient cooling.
3. Is the original design placing too much stress on two MOSFETs? It seems a low number of devices. What is their role? Or is it just two getting hot out of six?

[Smiffy]

Re: BF6 Mosfets

HI Guys
Thanks for all the help and info.
Heres a link to a pic of the BF6 as I havent got a dig camera at the mo

http://www.firingsquad.com/hardware/bf6/images/bf6.jpg

The blown caps are the three in front of the row of 12.EC10,EC11 and EC12.I'll replace them and then see what happens to the mosfets which are the 2 on the right of the atx connector.Im running at the mo in bios at 113Mhz fsb for 1470Mhz on 1.40v.Will possibly have to lower cap size as cant find 1500Uf 8mm andthose three are a bit tight on space.Can fit 10mms in all the rest by the look of it.
Ta for help
Smiffy

[Rainbow]

Re: BF6 Mosfets

I re-emphasise that you try to find out why the MOSFETs are getting hot before replacing.

It's easy - that board is not designed for Tualatin CPUs, there are only two MOSFETs for CPU power so they get hot when the current draw is high.

[Smiffy]

Re: BF6 Mosfets

Hi Rainbow
So its basically not designed to supply the current the Tualatin core needs.
Smiffy

[Smiffy]

Re: BF6 Mosfets

Hi Guys
Replaced the 3 caps.Only had 1000 uf but looks like Davemax was right.Mosfets much cooler now.
Ta all
Smiffy

[Smiffy]

Re: BF6 Mosfets

And have found out that the other 2 mosfets(55N03LTs) are providing the 3.3v line so as Rainbow says its pushing it for 2 mofets to supply the current.Will replace all the caps and heatsink the mosfets with some airflow over them as well and will see if it can cope with it then.
Thanks for all that helped with info.
Smiffy

[Neo2_000]

Re: BF6 Mosfets

It's easy - that board is not designed for Tualatin CPUs

Hi Guys,

Some time ago I finished a fun project where I used a slotket adaptor and a tualatin adaptor on a stock ASUS P2B mobo (Pentium II 350 MHz) to convert it to a Tualatin. The project was a success and my mates would spin out when they saw the display flash up 1200MHz on this old piece of crap

I was thinking of using the Tualatin CPU adaptor on an Intel D815EEA mobo, but am now having second thoughts after reading this.

Any thoughts?

[gg1978]

Re: BF6 Mosfets

Hi Guys,

Some time ago I finished a fun project where I used a slotket adaptor and a tualatin adaptor on a stock ASUS P2B mobo (Pentium II 350 MHz) to convert it to a Tualatin. The project was a success and my mates would spin out when they saw the display flash up 1200MHz on this old piece of crap

I was thinking of using the Tualatin CPU adaptor on an Intel D815EEA mobo, but am now having second thoughts after reading this.

Any thoughts?

THe thing with Tualitin core chips is not just that Vcore went down, and Icc went up, though not much, the thing is that they changed the GTL bus reference voltage, i believe for VRM 8.2 8.3 and 8.4 GTLREF is 1.5V, but for VRM 8.5 (Tualitin) they dropped GTLREF to 1.25V, and added another VID input. This is going from memory now though. Presumably having Vcore at 1.5, if the CPU expects 1.45 or 1.4V is no big deal, but i've heard that the .25V difference in GTLREF may be bad for the I/O buffers of the CPU itself. If you only have VRM 8.2 support, i believe minimum Vcore for those boards is 1.8V, which is very much in Tualitin frying range.

I never though Tualitins were very heavy on the Vcore Icc though, no more than a Katmai core chip anyway.

The thing is that most, if not all P3 class motherboards typically use a single phase VRM design, with the 8 pin SOIC MOSFET packages that don't do nearly as well as dumping heat as the TO218 or TO220 package provides.

[Rainbow]

Re: BF6 Mosfets

Hi Guys,

Some time ago I finished a fun project where I used a slotket adaptor and a tualatin adaptor on a stock ASUS P2B mobo (Pentium II 350 MHz) to convert it to a Tualatin. The project was a success and my mates would spin out when they saw the display flash up 1200MHz on this old piece of crap

I was thinking of using the Tualatin CPU adaptor on an Intel D815EEA mobo, but am now having second thoughts after reading this.

Any thoughts?

It's Intel board - any CPU not specified to work by Intel will probably not work. Intel boards can happily start up and say in the POST that the CPU is not supported.
Asus P2B is not a piece of crap, I'm running Celeron Tualatin on that too. At 1.8V as mine can't do less (the latest versions can, however).
In fact, most non-big-brands-like-Intel P2 and P3 boards use TO263 mosfets.

[Neo2_000]

Re: BF6 Mosfets

http://www.hardwarecooling.com/produ...ket_370_FC-PGA

Thanks for the replies guys. Here is the type of adptor I am talking about.

Adapts Socket 370 motherboards made for FC-PGA processors for use with FC-PGA2 (Tualatin) processors

http://hardware.mcse.ms/message195198.html

In reference to the D815EEA:

the Tualatin adaptor (Upgradeware and Powerleap) have both been tested to work on this motherboard using BIOS P10, which I have.

(I have yet to verify this experimnetally)

The adaptors do have some circuitry so I think that they must adjust the voltage down for the Tualatin core - otherwise what possible use are they?

My general concern is with Rainbows statement:

It's easy - that board is not designed for Tualatin CPUs, there are only two MOSFETs for CPU power so they get hot when the current draw is high.

After reading this, my concern is not that the motherboard bus voltages may stress the processor, rather the opposite: that the demands of the processor might stress the motherboard. Shoud I be comncerned about this and how can I determine whether the D815 has the necessary hardware to supply the Tualatin? Do Tualatin boards have more FETs than copermine boards?

P.S.

Asus P2B is not a piece of crap, I'm running Celeron Tualatin on that too. At 1.8V as mine can't do less (the latest versions can, however).

From memory you can mod the older boards to deliver the correct voltage. If you are interested, I will see if i can dig up the web reference.

[Rainbow]

Re: BF6 Mosfets

If it was tested on that Intel board, then it should work for you too. Maybe they forgot to disable that in the BIOS

After reading this, my concern is not that the motherboard bus voltages may stress the processor, rather the opposite: that the demands of the processor might stress the motherboard. Shoud I be comncerned about this and how can I determine whether the D815 has the necessary hardware to supply the Tualatin? Do Tualatin boards have more FETs than copermine boards?

Some Tualatin boards have 4 MOSFETs, some only 2, but better (lower Rds(on), higher current rating).
I've had BE6-II for repair with shorted MOSFETs that was used with Tualatin for some time.

[Neo2_000]

Re: BF6 Mosfets

http://hardware.mcse.ms/showthread.php?threadid=208649&perpage=10&pagenumber=1

Unfortunately the problem could be that the Intel BIOS simply doesn't
support Tualatin processors correctly - certainly they aren't officially
supported. The Tualatin also uses a lower Vcore than the minimum
specified for the motherboard (1.5v vs 1.65v), and draws slightly more
than supported current (~20A vs 18.2A) What does the BIOS show for
processor type and speed when the Tualatin is installed?

You could try the latest BIOS version (P11), but I doubt that will help
- in fact it may stop the board from booting at all since one of the
changes between P10 and P11 was "Added prevention of using Blocked
unsupported processors."

Looks like this guy had stability problems. Reference to BIOS upgrade locking out unsupported processors as Rainbow said.

Note also the reference to the supported current for the D815EEA being exceeded by Tualatin demands. ~20A vs 18.2A