Closed Looking for some motherboards/parts/etc.....486/Socket 3 era

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creepingnet

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The one on my FIC 486-PVT has this that broke the other day, it's used to switch between RN16-RN19 which selects the CPU type. Was just upgrading from an intel 80486 DX2-66 to an AMD 80486 DX4-100 100SV8B. May be trying some other chips as well at this point. I also would not mind getting my hands on another FIC 486-PVT as well to use as a spare/backup as I'm not 100% sure the board I have is functioning right - after upgrading to the AMD DX4-100 with a soldered on pin on the Resistor network, the machine locked up and stops POSTing all of a sudden while playing some games in Windows 3.1.

Testing the "Resistor Network" with a Multimeter shows 0.0003 Ohms Resistance and each group of 2 pins side by side is basically a "jumper" inside of the module. I think it's just supposed to be a 0 Ohm "resistor network" designed to jump a set of contacts. Using Staples as jumpers gives EXACTLY the same reading. Unless this component is actually damaged and should have some sort of resistance reading, but given the FIC manuals I've looked at that actually tell what these probably at, it's a 8P4R SIP (8 Pin 4 resistor Single inline Package).

Also looking to get a proper thermal unit, currently I've been using old Cyrix DX-2 66 stick-on heatsinks with 3-pin project fans from Vetco to do the job, works okay with my DX2-66 but not sure if I killed the AMD DX4-100 or not. It was running great for a few hours.

Looks Like This
IMG_20170214_011308710.jpg

And goes to the red square area of 8-pin jumpers up here
IMG_20170120_164711264.jpg

TLDR: Looking for 8-pin Resistor network used on First International Computer Motherboards (FIC) for CPU type selection, possibly another FIC 486-PVT board, and maybe a 486 Heatsink/Fan assembly that's actually suited to use with a DX4-100 or faster CPU.
 
im pretty sure the Cyrix DX2-66 is a 5 volt chip the Intel DX2-66 is a 5v chip and the AMD DX4-100 and Intel DX4-100 are 3.3 volt chips,, did you change the voltage on the board before it died???
 
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im pretty sure the Cyrix DX2-66 is a 5 volt chip the Intel DX2-66 is a 5v chip and the AMD DX4-100 and Intel DX4-100 are 3.3 volt chips,, did you change the voltage on the board before it died???

The DX2-66 is acutally an Intel with a Cyrix heatsink on it. I work in Redmond, and we have a local electronics shop called Vetco that has a sizeable New-Old-Stock of 486 CPU coolers, all stick-on adhesive ones with the Cyrix DX2-66 plaque on them, I took it off because I stuck it to the Intel for lack of finding any real active heatsinks locally, and screwed a proper 3-pin project fan on it.

Yes, I changed the settings - actually documented what I did in my blog here - http://creepingnet2017.blogspot.com/

The main settings to change from the Intel to AMD are

JK1-JK4 - Stay the same - that's the Bus Speed (33MHz)

JCV1 and JCV2 (CPU Voltage)
i80486 DX2- JCV2 on Pins 2-3, JCV1 = NC (oddly it's a 5V CPU but was running rather happily under 3.3V)
AM80486 DX4-100 100SV8B - JCV2 on Pins 1-2, JCV1 = NC (CPU is 3.0V according to top)

RN16-RN19 = CPU Type
Intel 80486 DX2 - RN19 On, RN18-16 Off
AMD 80486 DX4 - RN19 off, RN18 on, RN17 and RN16 off

Nothing else needed changed.

What initially tipped this off was that RN16-RN19 (the 4 8-pin headers next to the CPU) has a single "0Ω 8-Pin 4 Resistor Network" or 8P4R provided by FIC to set the CPU type. The frontmost pin broke off this and I jury rigged it with a piece of soldered wire I stuck in the hole and held against the broken contact with friction. It worked, for several hours at least.

At that point I setup the DX4-100 in the BIOS, WriteBack Cache, Cache timing set to Turbo, Memory Speed set to Turbo, and my god did it run great. Then it went to sleep (Ecologic bundled with AfterDark under Windows For Workgroups), I woke it up, switched ports in the back on the SoundBlaster card b/c it was night and I use the Line-Out to get less volume (unpowered speakers), and it hung, cursor in the center of the screen, nothing would bring it back except pressing the reset button which then it stopped POSTing and has not ever since.

There are some signs of life such as the keyboard lights blinking when the power switch is flipped, which means it's getting to the Keyboard controller part of POST, but it's not getting much further than that, still waiting for video to initialize.....which it's not. the DX2 won't boot either the last time I tried for some reason...which is odd. I have a POST card coming in so I can figure this stuff out without all the needless fiddling to figure it out. I have a small theory it may be the CMOS and those Cache settings I put in to try and take advantage of the new CPU features (and maybe inadvertently sent it careening at the L2 Cache in the process, and it just happened to hit the improperly configured L2 Cache with the wrong chips in it (one 16Kx8 and 4 8Kx8 - the TAG has to be 32Kx8 and the other four at least 16Kx8 per silkscreening on the board. I read that this was sometime BEFORE the video card gets initialized so that could be the cause.
 
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