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K6 mods for I-Opener
Overheating problems

New MessageK6 mods for I-Opener (modified 0 times) BadFlash
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After doing some extensive experiments using a K6-III+ running at 2V I need to warn users that even 300Mhz may be too fast due to Q16 heating.

I found some power MOSFET's with better specs than Q16. My bright idea was to solder these in parallel with Q16 and mount a heat sink on it. I figured if I could find a MOSFET with higher conductance at the same voltage as Q16 most of the heat would go to it rather than the real Q16 as its resistance would be lower at the same bias level. I was hoping to avoid lifting Q16, mounting a cooling resistor, and lowering the core voltage. My heat sink was around 2" square of 10 mil copper. I bypassed the overcurrent cut-out with a .06 ohm smt.

I fired it up and all seemed fine. I warped up to 450 Mhz and all seemed fine, then the power supply crowbar'd and refused to reboot. I opened up the box and found that my new Q16 was so hot the solder had melted and the heat sink shorted something out.

I decided to solder a copper heat sink to the solder tab at the top of Q16. Attempting to cool it through the plastic case is very ineffective, but you can solder directly to the tab at the top. My heat sink was 10 mil copper again, 1/4" wide and 1.5" long. I bent it in an "L" after soldering it so it would fit under the RF shield. I fired up the board and kept it at 300MHz (100X3)for 5 hours. Motherboard Monitor gave me steady-state temps of 180 degrees F running a continuous loop of Windows Media Play, full screen + full volume sound. The heat sink was too hot to touch. I had no way to get a direct reading, but it was higher than 180 degrees for sure.

Anyone running at 2V should be warned that all that heat is going right into the motherboard. I suggest making some attempt to add heat sinking and forced air flow. I am looking into small 25mm 5V fans at this time to mount at the top of the I-O.

Bottom line is that you are at risk without serious airflow AND heat sinking if you run at 2V. It appears that use of a cooling resitor and lifting Q16 and adding heat sinking to it is the only good way to date to get serious speed. No amount of bypassing will allow you to stay above 400 Mhz without reduced core voltage.

It looks to me like the real answer is something like a powerleap socket to fit in the I-O.

12-26-2000 09:32:32

New MessageRE:K6 mods for I-Opener (modified 0 times) Linuxguru
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You can't solder power MOSFETs, even the same type, in parallel. At the least, you will need small resistors in series with each source to avoid current-hogging by one of the two FETs.

The specs of the original FETs are fine. This is a linear circuit, and there is no way to avoid the power dissipation due to VI. The only option is to reduce I, which is a function of Vcore and the CPU type.

12-26-2000 11:56:19

New MessageRE:K6 mods for I-Opener (modified 0 times) ASPguy
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i have an amd 333 mhz afk chip running at 3x95mhz at a vcore of 2.17. it run stably at temperatures of about 58c and 45c cpu or system can't remember.

anyhow, is my vcore okay? or is badflash refering to my vcore?
i have no other cooling besides a sunon fan on top of the cpu. it has it's own heatsink, the original iopener heatsink is no longer in there.

i can also use softfsb to bring the 95mhz to 110mhz and it seems to run okay, heat goes up eventually though to about 65c.

12-26-2000 12:12:55

New MessageRE:K6 mods for I-Opener (modified 0 times) BadFlash
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Linuxguru, that was exactly my plan, and it worked. I used a Mosfet with better specs to be sure it happened. I wanted all the power to be dissapated in the piggyback MOSFET to keep the heat way from the board. I am also familiar with ohms law. Q16 is dropping 1.3V at around 5 amps. That is 6.5 watts. My point was that if the piggyback chip with a couple of square inches of heat sink is getting hot enough to melt solder, the same amount of heat is being absorbed by the motherboard.

ASPguy- I'm talking about a K6-III+ with a Vcore of 2V. A normal K6 runs a 2.2 volts. This means that if you draw the same current your Q16 is dropping 1.1 volts and need to get rid of 5.5 watts. 65C is 149F. If you figure that is around a 80 degree rise over air temperature, If you figure the larger wattage on Q16 you can see that it gets hotter in my application.

Bottom line is that if you want to cool down Q16 with a K6-III+ you must drop the core voltage to reduce the current draw or find another way to get current to it. My results have been very poor at dropping core voltage. All K6-III+'s are not created equal. The ones I have won't post below 1.9 volts, so I'm stuck.

12-26-2000 14:15:28

New MessageRE:K6 mods for I-Opener (modified 0 times) Turbo3
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Just bite the bullet and lift Q16 and put in the dropping resistors. This is the easiest and cheapest way (resistors cost <$1) to drop the voltage and get rid of the heat. Just heat each of the two pins on Q16 until the solder melts and then bend the pin up just a little. You are not trying to lift the pin clear of the pad so there is no solder connecting it. Just a few thousands of an inch so you can slip a shim of metal between the two. The shim is what breaks the solder bond. Once the two pins are free you can then heat the big metal tab to remove Q16 from the board. Use solder wick to remove the solder from one of the two small pads and add solder to the other. Now solder Q16 back by standing it up and heating the pad with the solder. You can easily adjust the position of Q16 until it is standing straight since it is held on only one pad. When it is the way you like then add solder to the other pad. Next add in the resistors between the board and large tab of Q16 and add a heat sink to the tab as well. Place the resistors between the CPU Fan and the top of the case just above the LCD cable connector. Use heavy gauge wire when connecting the resistors (they need to carry 5-7 amps).

I too had my heatsink melt off of Q16 when I tried to do this without the dropping resistors. There is no need to look for a better Q16 in the hopes of avoiding ohm's law (Power = Voltage times Current). As Linuxguru has pointed out, the only way to keep the heat out of Q16 is to reduce the voltage drop or lower the current. The resistors are just the best way to lower the voltage before it gets to Q16.

I do not try to boot at 500MHz but at only 300MHz. I then use K6CLK to change the multiplier from 3x to 5x in the autoexec.bat file. I have never been able to post above 300MHz with a 100MHz bus speed.

Outside in the Philippines were it is already hot the highest temp I have seen using this setup at 500MHz is 139F.

12-26-2000 19:06:16

New MessageRE:K6 mods for I-Opener (modified 0 times) BadFlash
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That was what I was getting at Turbo3. I guess I am not communicating too well in this thread. I guess most folks forget I suggested the cooling resistor idea (http://www.linux-hacker.net/cgi-bin/UltraBoard/UltraBoard.pl?Action=ShowPost&Board=technical&Post=1732 ). I am fully aware of where the heat comes from. I just didn't realize that 6 watts would get anything that hot. What I was trying to do is see if there wasn't another way to skin the cat, but I am now convinced that the cooling resistor is the way to go until I can get a 2V switching power supply on line that will fit in the case. I can't get the reduced voltage trick to work reliably with the batch of K6-III+'s I have, so I am assuming I am not alone. I've tried 3 different K6-III+'s in 3 different I-O's and none will boot below 1.9V. Most folks will be unwilling to de-solder Q16. The signal pad on pin 1 is very easy to destroy, so caution is advised. Some sort of support is also needed for the chip once it is standing up if you are hanging a heat sink & resistor off of it. There is still the issue of heat removal from the case.

Anyone calculate the heat sink area needed for Q16 with a cooling resistor? Turbo3- your picture looks like you went a little overboard.

12-27-2000 10:38:00

New MessageRE:K6 mods for I-Opener (modified 0 times) Turbo3
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Yes you are correct that you were the one to suggest using a resistor to drop the voltage. If you follow my directions there is no danger of damaging the two pin pads as you apply no force to them. You melt the solder on the pin and then lift it a few thousands of an inch. The metal shim breaks the solder joint and all the hard work is done. No support is needed once Q16 is standing up (the heat sink mounts to the socket 7 and just connects to the tab of Q16, so there is no load on it). Just melt a large amount of solder on each pad to surround all four sides of each pin. The heat sink for Q16 is just a folded piece of sheet copper fan folded to go the length of the CPU fan/heat sink. This way it gets cooled by the exhaust air from the fan. It would look strange if it only went 1/4 or 1/2 of the way across so I just made it go from one end to the other. If works so I have never gone back to do it another way. I have perhaps 12 feet of this 3 inch wide copper sheet so this is a tiny fraction of what I have available. As for getting the heat from the resistor out of the case, placing it at the top of the case in the air flow from the other side of the fan takes care of that problem. Heat goes up so you want the heat source as close to the top as possible. I also enlarged all the RF shield holes on the top to slots that match the plastic cover openings. This works very very well and you can really feel the heat coming out the top. I have three other K6-III+ modules and when I get back to the states I will upgrade another iopener to this level and run these three modules through it. But most modules should run at +/-10% and certainly at +/-5% unless we actually bought out of spec parts from that LA store. As I recall they were sold "as is". But with my setup you should be able to run at 1.9 volts and still keep Q16 and the motherboard temperature down.

Its your statement here:

"It looks to me like the real answer is something like a powerleap socket to fit in the I-O."

that I disagree with. Going with the resistor (your original idea) keeps everything within the case and you don't need an external 12v supply for the Powerleap. Except for the intake hole cut in the back cover, my 500MHz iopener looks like a stock one.

12-27-2000 18:02:37

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