myne wrote on 2026-06-06, 00:28:

yay
So... I was accidentally on the right track when I asked about the xtal 🤣

Well maybe it helped indirectly by making me wonder what's that OSC pin... 😁

Apparently most Sound Blasters don't use that as they have their own crystal oscillator, but AWE64 does need it. I guess it was some cost-saving measure.

myne wrote on 2026-06-06, 00:29:

Now you have to write a how to guide for the next guy in 6 years who googles "how do I...?"

I already wrote about it on this thread, where it might be easier to find than here.

ADD AN ISA SLOT TO A MOTHERBOARD ???? Gigabyte Ga-7ZX

Chkcpu wrote on 2026-05-31, 19:47:

Thanks for reporting your test values. So a 2.2V setting was not among them, but you found a nice 2.04V setting for a K6-2+! :) […]
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Thanks for reporting your test values.
So a 2.2V setting was not among them, but you found a nice 2.04V setting for a K6-2+! 😀

I’m sorry to hear the board won’t boot. The CMOS backup battery inside the DALLAS or BENCHMARQ RTC chip is probably dead. This sometimes causes a board to stall early during the Power-On-Self-Test.
Do you have a POST analyzer card to see where the boot process hangs?

Cheers, Jan

Ok, I got the board working again. It must have been the RTC, because it posts now with the external battery hooked up. I continued testing. Here are more results (minus what is already documented in the manual):

(Previously tested)
JV4-5 OPEN JV6-7 CLOSED 1.93v
JV4-5 OPEN JV6-7-8 CLOSED 1.73v
JV4-5 OPEN JV7-8 CLOSED 2.04v
JV4-5 OPEN JV6-8 CLOSED 1.95v

(More tests)

JV4-5 OPEN JV6-7-8 OPEN 4.05V
JV5 CLOSED JV6-7-8 OPEN 3.60V
JV4 CLOSED JV6-7-8 OPEN 3.51V

JV5 CLOSED JV6 CLOSED 2.06V
JV5 CLOSED JV7 CLOSED 2.19V
JV5 CLOSED JV8 CLOSED 2.22V
JV5 CLOSED JV6-7 CLOSED 1.77V
JV5 CLOSED JV6-7-8 CLOSED 1.65V
JV5 CLOSED JV7-8 CLOSED 1.85V
JV5 CLOSED JV6-8 CLOSED 1.79V

JV4 CLOSED JV6 CLOSED 2.05V
JV4 CLOSED JV7 CLOSED 2.17V
JV4 CLOSED JV8 CLOSED 2.20V

So at this point it seems pretty clear that everything open gives you the highest voltage (I didn't want to push the P166MMX I had in there too much with further high voltage tests) then JV 5 drops the voltage by a certain factor, JV4 by a little more, probably JV4 and 5 both closed is going to bring it down even further, and the JV 8, 7, and 6 drop the voltage further incrementally more in that order, with combinations being additive.

So then just to be clear, even though I can derive the 2.2v for my K6-2, you would advise against running it on this motherboard, due to the heat issues on the voltage regulator? Bigger heatsink on it or active cooling probably wouldn't make a difference?

sizzlinbeef wrote on 2026-06-09, 17:52:

So then just to be clear, even though I can derive the 2.2v for my K6-2, you would advise against running it on this motherboard, due to the heat issues on the voltage regulator? Bigger heatsink on it or active cooling probably wouldn't make a difference?

Thanks for all Vcore test details! Now you have a lot of values to choose from. 😀

About the useability of the 2.2V setting for a K6-2, this depends a lot on the Power transistor that regulates the Vcore, and how it is cooled. Can you tell us the part number of transistor you did the voltage measurements on and also look at the other power transistor next to it?
This may help answering your question.

Note that under load the Pentium-MMX 233 can draw up to 6 Amps at 2.8V, but the K6-2/400 consumes up 11 Amps at 2.2V. The regulator transistor must be rated to handle this current, otherwise it will quickly fail.
Then there is the amount of heat that is generated and needs to be removed by the heatsink. On these boards, the power transistor that regulates the Vcore is usually supplied by the 5V rail from the PSU.
For the 2.8V Pentium-MMX the voltage has to be lowered by 2.2V, so at 6 Amps this will cause 13.2W of power to be generated in the regulator transistor.
For the 2.2V K6-2/400, this will amount to 2.8V times 11 Amps is 30.8W!

I hope this illustrates my concern for the linear regulator on this board. 😉
But if the regulator can take the current, a bigger heatsink and active cooling could make a difference.

Cheers, Jan