VOGONS


First post, by Hoping

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Hi, I've had this board for some time and it came with a 486dx2-66. Now I want to mod the board to use 3.3 volt cpus. After searching over the net I concluded that the needed voltage regulator is a MIC29152 so I've bought a MIC 29302 to be on the safe side if I want to try some overclock. But As I've thought after soldering the voltage regulator and setting the jumpers for 3.45 volts on the cpu socket there are still 5 volts so it seems that the missing resistors near the voltage jumpers are necessary but I can't find a clear enough image of a CH-498B rev 2.0 to know the values of the resistors. I think that the capacitor at C23 is not necessary because on some images I've found it is not present.
So I'm thinking if anyone has the rev 2 board and can take a picture of the zone around the voltage regulator to see the values of R20,R21,R67,R68 and R69.
Thanks.

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Reply 2 of 5, by computerguy08

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I had to do a similar mod to my Jetway board, which you can find here: http://www.win3x.org/uh19/motherboard/show/5505

In the unofficial manual, I explained my way of modding the board with a voltage regulator, by replacing one of the resistors with a potentiometer, so I could adjust the voltage to my desire.

In your case, the IC's datasheet would help you understand where to install those resistors.

Reply 3 of 5, by Hoping

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My board is a REV 1 and only supports 5V, REV 2 boards support 3.3v.

I tried to make the mod but it is not that I have deep knowledge of electronics, and I did not succeed. From what I understood the voltage is taken from the difference between R20 and the other resistors that are selected with the jumpers. It seems simple but I tried two trimmer potentiometers and I was not able to get values higher than 2.5 volts.
So either I don't understand correctly how it works (very likely) or the two MICs I bought were faulty.
Due to frustration, I left the project and continued with other pending things.
In the future when I feel like it, since there is always danger of damaging the motherboard, I will try again, this time with an LT.

Reply 4 of 5, by ViTi95

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Just found that my CH 498B is also a Rev 1.0, and yes you're right, I tried one 3.3v and it didn't boot, so it doesn't support any 3.3v~4v cpu. I guess i'll stick with 5v processors, just bought an AMD 486DX2-80 (25220 E6) and it should be powerful enough for most of the games of that era.

Reply 5 of 5, by Hoping

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Well, I did something crazy, an Intel 486dx4 100 with a big heat sink and fan at 5v, and since it was already overvolted, why not setting an 40mhz fsb, and well its wonking, stable and cold.
This madness was due to the fact that I read that intel cpus tolerated 5v and that some member of the forum was using a 3.3v cpu at 5v for years without realizing it.