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 4, 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 4, 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 4, 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.