i'm no expert with mosfets but check the capacitors around it.

maybe these mosfets run hot. if it's getting to 80deg c then even a heatsink might struggle.

what voltage you running the cpu at? auto? if so, set it manually. it could be buggy.

foil_fresh wrote on 2020-03-11, 05:37:

i'm no expert with mosfets but check the capacitors around it.

maybe these mosfets run hot. if it's getting to 80deg c then even a heatsink might struggle.

what voltage you running the cpu at? auto? if so, set it manually. it could be buggy.

Checking the capacitors is a very good start. If capacitors are dried-out or bulging, their capacitance is lower, thus stressing the MOS-FETs more.

And - which CPU at which voltage?

Cant remember if it was set to auto, The caps looked fine but i will replace them since probably those are 20 years old already. I was testing it with a k6-2 500.
i hope i can fix it because ss7 boards are not easy to find here, and the 2mb version is way more difficult

A heatsink on the plastic part of the mosfet's case isn't as effective as a fan blowing air on that area would be. And yeah, change those caps.

My bet on half-dead mosfets. Do they heat up instantly after booting up?

quicknick wrote on 2020-03-11, 22:06:

A heatsink on the plastic part of the mosfet's case isn't as effective as a fan blowing air on that area would be. And yeah, change those caps.

A fan without a heatsink is pretty much useless. The whole point of a heatsink is to avoid hot-spots on a component - something no fan can ever achieve. Also, it helps dissipate heat by providing a large surface. So either heatsink or heatsink + fan. Fan only is silly.

No it's not useless. I've used this method countless times over the years, and around here I've seen it recommended more than once as the best way to cool down boards such as the Voodoo2.
In fact those mosfets already have some "heatsink" attached - the large copper planes that they're soldered to. The plastic case on a mosfet is not its hot-spot. The metal tab is.

Pabloz wrote on 2020-03-11, 05:05:

Hi guys, i have a fic-pa2013 mothertboard, very hard to find , and its the 2mb version. I know these boards are very expensive. […]
Show full quote

Hi guys, i have a fic-pa2013 mothertboard, very hard to find , and its the 2mb version. I know these boards are very expensive.
The problem i have is that one of these 2 mosfets gets hot like crazy, im talking about more than 176 degrees F.
with such high temperature you can even touch the back of the board and burn your finger.

i am wondering if anyone in the forum has that board and noticed it, or perhaps it is faulty on my board only.
should i buy a replacement mosfet or put a aluminum heatsink on top of it?

Not sure where you ended up with this, for reference I recently recapped my v2 and the vregs barely get warm with a k63+ 450 at 550 at 2.1 volts. Keep in mind I didn't replace the tiny caps though.

Hi guys, thanks all for the reply on this topic

i was able to finally buy replacement capacitors for this motherboard, and because of the pandemic i managed to have time and exchange 5 caps, which are the ones that are near the mosfets.

The result was still ..BAD

on the image i posted, the mosfet on the top gets to 60-65 degrees celcius, the mosfet at the bottom gets to 80-or 90 degrees celcius.
the board works, i left it running for 20minutes playing doom. But the amount of heat that it ends up with is tremendous.

After turning off the power supply , i touched the back part of the motherboard where the mosfet is , and its relly hot.

mosfets have these markings (picture attached) Im open for suggestions, should i find replacement mosfets? do you know what current mosfets on the market can i use for replacement?
or maybe i should buy some expoxy thermal compound and attach a heatsink on the black part of the mosfet?

Im asking this because the motherboard is very strange to find and i want to keep it good as much as i can.

processor installed is a amd k6-3 / 400 , 2.4v core

jumpers are
voltage jumpers set at 2.4v
nbclk1 2 and 3
sdram 2 and 3
nbclk2 1 and 2

sram 1 and 2

freq1 2and3
freq2 1 and 2
freq3 2 and 3

clk1 1and2
clk2 1and2
clk3 2and3
clk4 1and2

so i totally forgot and in a box i found another of these pa2013 boards,
but my second one is rev 2.1 and only 1mb cache. (the one with heat problems is rev 2.0 and 2mb cache)

used the same cpu, same jumper configuration and there was no heat problem
i checked the mosfets of the second board and found out that they used another brand

PHB
55N03LT
PHm9940 C5
Phillipines

so it seems that from version 2.0 to 2.1 they changed mosfet provider.

im wondering if anyone in the forum has this board, can you share what mosfet do you have?

I have a REV 2.0E-0036 of this board:

It's currently in use with original caps, using a K6-2/500 and Voodoo Banshee.

I am not where that PC is located currently, but if you can wait for 2 days I can check the part number on mine but I can't honestly give you a temperature reading on mine as I don't have the equipment. And regardless, 50C and 80C will burn a finger just the same, so a touch test also sounds pointless?

I have attached the datasheet, 175 Degrees C operating temperature.

Just put a heatsink on it and should be ok.
You could also measure it with a multimeter, there should be no short circuits between any
of the pins.

i have seen this problem too on some of my boards, and also on a tnt2 videocard. I even tested with multimeter to find continuity between legs and there was none.
where the PCB is from one original color , and because of heat that area of he pcb changes its color.

To be honest i really think that 175 Degrees C is too much, specially to all the rest of components that are near the mosfet, including plastic, I wonder if this was common during the year 2000 ? to ship boards with a lot of heat components? It works but at the end you know that heat is bad for electronics

I would also like to know how to fix this, because the black plastic piece of the mosfet is not the correct part to dissipate heat, real Heat is Below (what is soldered directly into the motherboard)

During the first pentium era and 486 era we normally saw a piece of heatsink with a nut and bolt, the old style voltage regulator where the piece has 3 legs and you can solder it to the board and attach a heatsink. Dpack mosfets are different as the metal piece go down against the motherboard.

I have not seen any mods done with dpack mosfets, but it might be possible to remove it from the motherboard, bend a little bit the 2 legs and put it in vertical position with a good heatsink soldered to the bottom of the mosfet. That with a good old style 486 voltage regulator should be good, and make sure the area has air flowing.

Just make sure you have good airflow over the area and the temperature will drop to manageable levels.

Just because a part is able to withstand 175 degrees C is not a reason to have it running near that (I've seen MOSFETs that unsoldered themselves due to extreme heating). If you look further in the datasheet above, at 175 deg. C the device becomes unable to pass current (drain current drops to zero).

(If one was needed), here's proof that a simple fan provides enough cooling for things lacking a heatsink.