M571 and K6-3 with a 2.4 vcore...

**alan_smithee** · #1 09-01-2002, 03:29 AM

Hello all, I recently got an offer for an AMD K6-400 AHX chip for $10, but it appears my board (PcChips M571 ver 7.0a) only supports a 2.2, 2.8, 2.9... vcore. Thus, will it run at 2.2 when it wants 2.4 or will this cause problems ? I tried it and my system became rather unstable. I've got the chip clocked at 75 Mhz x 5.5 which seems to be happily thinking it's running 400 mhz. Is there something I can put on the jumper to knock it down a little (a small resistor or something to bump it down from 2.8?)...

Just curious, it may be easier to just search out the other chip (AFX which is 2.2 vcore)... Or buy another board...

Thanks to all in advance,
alan_smithee

**brad** · #2 09-01-2002, 03:55 AM

Yes, that will cause a lot of problems. The AFX version of the chip is more appropriate for your board but the problem is not insurmountable, as it isn't hard to get a 2.4 Vcore on a v3.2 or v7.0 board:

Remove all Vcore jumpers at JP6. Connect a 47K resistor across the 2.8 volt pins at JP6. That will result in ~2.4 volts at the cpu socket. Verify that it is between 2.35 and 2.45 with a DMM and trim the resistor value as necessary to get it within that range or you may well have stability problems. Shoot for 2.42 if possible.

Possible Vcore values derived this way can be found at:

http://members.dingoblue.net.au/~fra...1/voltcore.txt

For still more info on the entire Vcore subject:

http://members.dingoblue.net.au/~franczabkar/m571/

Brad

**alan_smithee** · #3 09-01-2002, 04:13 AM

I'll have to pick up some resistors and get back in touch with you! Thanks again...

alan

**jim chase** · #4 09-01-2002, 04:56 AM

I used the 2.4 vcore K6-3/400 on a v7 M571 with the 2.2 setting just as Brad said. It worked great, no problems.

With a 47k resistor (I may have used a 100k?) jumpered across the 2.8vcore pins I was able to overclock to 450mhz, 75fsb x 6.

For $10.00, that's a steal, use a big heatsink and thermal paste.

Jim

**fredster2** · #5 09-01-2002, 05:06 AM

Hello alan

Your k63400 chip with a 2.4vcore should first be tried with the 6 x66 = 400mhz settings, using 5 1/2 x 75mhz = 412.5 mhz overclocks this chip and it will may respond by being unstable. I have this exact chip and board and I could not get it stable at 412.5Mhz. This chip is sensitive to overclocking. You may very well have to use the resistor modification to achieve stability, but I suggest you give this a try first. Note set the jumpers as for a K6 with 2 times(the K63 will see this as set for 6x at 400Mhz.)

fredster 2

**alan_smithee** · #6 11-01-2002, 06:22 AM

Well, it's working okay (I locked it up running some processor intensive multitasking), but that also could have been due to windows... But until tomorrow when I get to steal my friend's soldering gun it'll just have to be said that at a slower speed it still runs much faster than my other chip (previously a 300 Mhz w/o MMX). Does anyone know if running it at a lower core voltage will cause it problems. I know brown outs are bad for systems, and exxentially I"m continuously running it with not quite enough...

The other question I have is where do I test the core voltage, exactly. Do I connect the resister and then check on the two pins or is there a specific spot on the socket I need to place the meter?

Figured better safe than without a system...

Thanks again! All of the suggestions are greatly appreciated!
alan

**brad** · #7 11-01-2002, 07:24 AM

Yes, a K6-2 or K6-3 is often unstable (sometimes unusable) when Vcore is more than .05 or so below AMD spec. Some boards aren't happy with Vcore being on the money for that matter but most run best when it is .02 or so high. Thats why I recommended 2.42. The effect of a low Vcore doesn't often show up at lower speeds but does at 400 and above.

Where to measure? Its been quite a while since I messed with a M571 but if memory serves, the easiest place is JP8-A pin 3 or JP8-B pin 3. You'll know which pins are Vcore when you start measuring because the wrong pins will measure around 3.4, the fixed I/O voltage. Measure your new 2.4 volt Vcore after installing the 47 K resistor of course.

BTW, Franc Zabkar did all of the Vcore (and much more) research work on this board and you can access it at:

http://members.dingoblue.net.au/~franczabkar/m571/

The part of the circuit we've been talking about here is at:

http://members.dingoblue.net.au/~fra...1/pwrnotes.txt

Enjoy....

Brad

**fredster2** · #8 11-01-2002, 07:30 AM

alan

Just a note about soldering, do not solder on the circuit board or on the jumper pins on the board, instead use external jumper pins to solder your resistor to them and then plug in your resistor with the jumper pins to the board. Also I think it would be ok to run your chip at 2.2v even if its rated for 2.4v but I'm not completley sure. Why don,t you run this chip at the 6 x (which equals the 2x setting), instead of the 5 1/2 x you are running now.

fredster2

**jim chase** · #9 11-01-2002, 07:21 PM

I agree with fredster2, don't solder on the M/B. I used an old turbo led jumper to attach the resistor, just solder the resistor to the turbo jumper leads then plug the jumper onto the 2.8 vcore pins.

Will a low core voltage cause a problem? If the system is stable it's no problem, but I doubt it will be stable.

Jim

**cjpat55** · #10 19-02-2002, 09:58 AM

Hi all,
I appear to have come up against a similar problem except that my 571 board is ver 3.2a.
What resistance would I have to put in to acheive the required 2.4Vc for my board. Is it the same value as given for the 7 version.
Any advice appreciated.
thanks
cjpat

**brad** · #11 19-02-2002, 10:36 AM

v3.2a and v7.0 boards share the same Vcore circuitry and support the same voltages, so just put a 47K resistor across the 2.8 volt pins at JP6. All other comments/recommendations apply.

Brad

**bear** · #12 19-02-2002, 11:55 AM

If you are located in the United States, you can get the necessary resistor at just about any Radio Shack store for around $0.69 for a pack of five.

For 2.4v:
47K-Ohm
1/4 watt
5% tolerance
Catalog No. 271-1342

for 2.5v:
22K-Ohm
1/4 watt
5% tolerance
Catalog No. 271-1339

The 47K resistor is the one I used on the 3.2a board. My 2.4v chip was just a tad unstable at 2.2v but is running very solid with the resistive jumper in place. If you want to attempt 450MHz with your chip you may have to go to 2.5v, in which case you would want the 22K-Ohm resistor instead (also jumpered across the 2.8v pins).

**cjpat55** · #13 20-02-2002, 12:20 AM

Thanks to you all for the advice.. i will give it a go
cjpat