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First post, by 9646gt

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I'm trying to build a 486 machine with the following:

32mb of RAM 72pin
DX4ODPR100 100Mhz 5v compatible overdrive CPU
256k of cache consisting of 4x KM68257BP-20 in first bank and 4x IS61C256AH-15N in second bank with TAG being UMC UM61M256K-15
ATI Graphics Ultra VLB upgraded from 1mb to 2mb of RAM
And on the Soyo board am using a ISA I/O card ( GoldStar Prime 2)

First motherboard: Micronics JX30WB VL-BUS (09-00192-xx) (sold as Gateway OEM pull from 4dx/33v model)

Everything boots to post screen. However the screen redraw in the bios setup is a slow one but one line refresh kind of like you'd see when redrawing a window in Windows without proper hardware acceleration. Having the HDD connected (onboard IDE controller as this board includes one) and trying to configure it in BIOS either as a custom model by entering the drive specs or using auto detect results in a hard system freeze. Even with the HDD disconnected it will freeze after the memory test completes. CPU jumpers are setup as a486DX2 66mhz as they should be for a ODPR overdrive.

Second motherboard: Soyo 025L

This board I get no display at all and no beeps. CPU is cold to the touch and jumpers (confusing on this board) are configured for 486 DX2 66MHz. I am using the GoldStar ISA I/O card I mentioned earlier in this board since it lacks a controller.

Neither board has any signs of damage and neither has ever had a Varta type battery installed so that can be eliminated as well. Both board were sold as used and working. The slow screen redraw and freezes with the firs motherboard are odd and I have NEVER seen a slow screen refresh like that in BIOS on any board at all. Any guidance moving forward?

Reply 1 of 6, by PD2JK

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Micronics board: How is the RTC doing? When this fails, you can get these symptoms. Also try a slower bus speed like 20 or 25 MHz if possible.

Soyo board: This board has a 5V - 3V voltage regulator. I don't know how it behaves when a Overdrive CPU is installed. Can you try a non-Overdrive cpu? See if the voltage regulator and CPU gets warm, if not; dead voltage regulator? Set JP24 accordingly.

When using the Overdrive, set the jumper to 5V. The Overdrive will do the voltage conversion.

i386 16 ⇒ i486 DX4 100 ⇒ Pentium MMX 200 ⇒ Athlon Pluto 700 ⇒ AthlonXP 1700+ ⇒ Opteron 165 ⇒ Dual Opteron 856

Reply 2 of 6, by the3dfxdude

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These two things are common issues with 486 systems. I'm mentioning these based on what you are saying about the Micronics board, but one these issues can be affecting either.

1) Most 486 systems have a turbo function. Make sure you are engaging turbo mode
2) Most 486 systems cannot accept EDO 72pin memory. Make sure you try known Fast Page memory in the board.

Reply 3 of 6, by 9646gt

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PD2JK wrote on 2025-06-13, 13:10:

Micronics board: How is the RTC doing? When this fails, you can get these symptoms. Also try a slower bus speed like 20 or 25 MHz if possible.

Soyo board: This board has a 5V - 3V voltage regulator. I don't know how it behaves when an Overdrive CPU is installed. Can you try a non-Overdrive cpu? See if the voltage regulator and CPU gets warm, if not; dead voltage regulator? Set JP24 accordingly. HOWEVER, I should also report that the CPU was being reported as 50Mhz on this board even wit the correct jumper settings which is odd

When using the Overdrive, set the jumper to 5V. The Overdrive will do the voltage conversion.

Thank you for the reply. I have a fresh external battery installed in the Micronics board. It's a 3cell lithium battery pack to replace the old alkaline one. I'll look and see if I can try the lower bus speed. I've never seen a screen refresh problem like this in BIOS before. I can confirm that the battery is working to the extent that the BIOS settings get saved on exit.

In the Soyo I do have a DX266 I can try when I get home. I do have the jumper 24 set to 5v

Last edited by 9646gt on 2025-06-13, 15:15. Edited 1 time in total.

Reply 4 of 6, by 9646gt

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the3dfxdude wrote on 2025-06-13, 13:22:

These two things are common issues with 486 systems. I'm mentioning these based on what you are saying about the Micronics board, but one these issues can be affecting either.

1) Most 486 systems have a turbo function. Make sure you are engaging turbo mode
2) Most 486 systems cannot accept EDO 72pin memory. Make sure you try known Fast Page memory in the board.

I will for sure have to test the turbo switch on the Micronics board. I know the cable for the switch is in the proper orientation. Also, the RAM that I purchased is FPM and is listed as 16MB 4Mx36 FPM Memory PARITY 60NS SIMM 72-PIN 5V

Reply 5 of 6, by 9646gt

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I got the Micronics board situated but it has a blue overdrive socket as the only socket so my CPU would never run above 50mhz in it.

The Soyo keeps giving me memory errors (long beep) now. I finally had it working minus the IO card not doing as it should which I guess was leading to the black screen after initial post. I figured out that one of the 72pin slots was causing errors because it stopped freezing with just one slot used. I notice the slot seemed just a tad loose so I tried to reflow the solder connection on the bottom and added some fresh solder but didn’t help and after booting a few times I’m now just getting a memory errors al together.

I found some corrosion on the cmos clear jumpers and cleaned the area with vinegar. It’s odd since it uses a coin cell but it may have leaked at one point me someone repaired it but the repair now is not effective. Who knows. Starting to think the board is shot.

Reply 6 of 6, by CkRtech

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9646gt wrote on 2025-06-14, 00:44:

The Soyo keeps giving me memory errors (long beep) now. I finally had it working minus the IO card not doing as it should which I guess was leading to the black screen after initial post. I figured out that one of the 72pin slots was causing errors because it stopped freezing with just one slot used. I notice the slot seemed just a tad loose so I tried to reflow the solder connection on the bottom and added some fresh solder but didn’t help and after booting a few times I’m now just getting a memory errors al together.

I found some corrosion on the cmos clear jumpers and cleaned the area with vinegar. It’s odd since it uses a coin cell but it may have leaked at one point me someone repaired it but the repair now is not effective. Who knows. Starting to think the board is shot.

I have an 025N2 that used to have a varta battery in that spot. It leaked and got into that clear CMOS jumper area among other nearby areas. Have you checked under the keyboard controller IC for more corrosion? How are your voltages looking? Even if the board never had a varta, perhaps another board that had a leaky one was stacked on top of it at some point.

Have you used the clear CMOS jumper on this board? I've seen an Award BIOS with BIOS defaults loaded + general tweaking seem to work OK most of the time after a battery replacement but still exhibit odd behavior on occasion until the CMOS jumper was used to truly clear things out followed by loading BIOS defaults.

Any photos, btw?