It's a Chicony motherboard.
Have a look here for perhaps a match: http://arvutimuuseum.ee/th99/#1
Could possibly be this one: http://arvutimuuseum.ee/th99/m/C-D/33303.htm
or this one: http://arvutimuuseum.ee/th99/m/C-D/31073.htm

Thanx for that I will study the links and material tonight when I get some time, from your knowledge do you think a intel overdrive chip could work in this board?
I got a dx40dpr100 dx40dpr75 and dx20drp66

I think I found it, looks like this one
https://stason.org/TULARC/pc/motherboards/C/C … 86-33-50-L.html

treeman wrote:

Thanx for that I will study the links and material tonight when I get some time, from your knowledge do you think a intel overdrive chip could work in this board?
I got a dx40dpr100 dx40dpr75 and dx20drp66

I see no reason why it shouldn't, since it was designed to work in older motherboards that only support 5V CPU's.
Just check the pinout of your Overdrive CPU's to ensure it is compatible with the socket of your motherboard (based on what you described, they are the ODPR chips which should work fine as a drop in replacement).
However, with such fast CPU's, you should actually pair it with a VESA Local Bus or PCI graphics card which, unfortunately, your motherboard does not have the slots for.

treeman wrote:

I think I found it, looks like this one
https://stason.org/TULARC/pc/motherboards/C/C … 86-33-50-L.html

Yes, it's the same one in my second link.

Thanx for your help yes I saw it on the second link through you then ended up on a different site for the same board, thanx for all your answers, ill try the overdrive see how it goes

I put the overdrive in, says its running at 66mhz on bootup, but sysinfo shows as dx4 75, so I guess that's the max this motherboard will run, also a score of 141 where a pentium 66 has just over 200

treeman wrote:

I put the overdrive in, says its running at 66mhz on bootup, but sysinfo shows as dx4 75, so I guess that's the max this motherboard will run, also a score of 141 where a pentium 66 has just over 200

Which Overdrive CPU did you put in?
For both the 66 MHz & 100 MHz Overdrive CPU's, set the jumper settings of the CPU speed at 33 MHz and I would set the CPU type as 80486DX.
The 75 MHz overdrive CPU runs at 25 MHz FSB (CPU speed).
What I do find odd is that, on this motherboard, the jumper selection for all CPU speeds from 20 MHz to 33 MHz is the same - so, I'm not sure how the motherboard "knows" what the FSB should be (unless it has some auto detect feature built in).
There are normally different jumper settings to select each FSB speed - perhaps check for more jumpers near JP12 that is not documented on the links that I provided or, in the BIOS settings itself.

It's also possible that your BIOS does not read the CPU properly since the BIOS predates when Intel released the clock doubled 486 CPU's - you could test with some benchmark utilities to verify the speed of the CPU.

I put in the dx40dpr100 in, the situation is also a little clouded because cpu came with bent pins from ebay, when fixing one pin snapped but its a outside pin and I soldered it, last pic, don't think that would affect the system seeing it wrong especially that boot screen says 66mhz but bench mark 75.

Yes I set the fsb jumper to 2-3 which is 33/25fsb hmm more like non 50 fsb

I will Probably try the dx50 in see what benchmark I get since it's a 50fsb cpu vs a 33? Fsb 75, only that repaired pin is holding me back a bit, but there is something more exciting about running a "overdrive" then just a normal 486

So I found a pin out, the soldered pin is ahold, I ran dukenukem 3d and doom for a bit the system didn't crash or freeze so guess its working fine, doubt it has anything to do with being detected as 75mhz, I saw a post on here from a guy that upgraded to a dx4 75 over driver and his test score was nearly the same as mine so it looks like its running at 75mhz, weird that is exact double of a dx33 on the benchmark which would be 66. Anyway thread has really gone off the rails, thanks again for helping me id the board which allowed me to swap the cpu, 75mhz is good enough for me.

Thats about it, oh if anybody has a idea what those 3 repairs or mods on the back are id be interested to hear.

Thank you!

You could try to use other benchmarks, like Navrátil System Information (NSSI). Its comparative CPU speeds should give you a better idea whether your CPU is running at the right speed.
However, the Overdrive 100 should run at 33FSB x 3 = 100 MHz with the Overdrive 66 at 33FSB x 2 = 66 MHz and the Overdrive 75 at 25FSB x 3 = 75 MHz.
Do not run your Overdrive CPU's at 50 MHz FSB.

Which graphics card are you using? Lacking a VLB slot, I hope you pop in one of the quicker ISA cards, like GD5434, ET4000AX, or ET4000/w32i. Might also try running the ISA bus at 10 MHz.

sorry for the late reply, didn't even realise there was a reply to this thread, had to turn on email notifications, they were off

so a little bit has changed since my last post, now running a amd 5x86 133 chip in with a Kingston tc voltage regulator at 33 fsb with a 66mhz chip I got.

I am waiting for a 40mhz crystal and going to try clock it to 160mhz, I also installed a larger heatsink and fan in anticipation.

also the card I am running is a tseng et4000 1mb isa - its the best isa card I have

How can I turn the isa bus to 10mhz? anything to do with the other soldered crystal of 14mhz?

As usual: did you already think about removing that barrel battery? Considering its age it will start at some point leaking! There are lots of different options to replace it with. 😀

Nowadays I simply use an AA shaped 3.7V Lithium battery with a diode to prevent charging on a small raster board.

I had a moment a few weeks ago when I desoldered all the barrel batteries from all my old motherboards and at exactly that time I was putting this board in then taking out again so as a temporary measure I removed the battery while it was out, soldered in 2 wires maybye about 5-6cm long soldered the barrel to them and twisted to the back of the case away from anything important.

would you be able to post a picture of your setup? I would be interested as what I have is temporary but safe

treeman wrote:

I had a moment a few weeks ago when I desoldered all the barrel batteries from all my old motherboards and at exactly that time I was putting this board in so as a temporary measure I removed the battery on this board, soldered in 2 wires maybye about 5-6cm long soldered the barrel to them and twisted to the back of the case away from anything important.

would you be able to post a picture of your setup? I would be interested as what I have is temporary but safe

I recorded a video of the battery replacement I am now using in my 286:

https://youtu.be/seCoC2AcHqs

I have later cut off the excess raster board and used double sided tape to glue the whole thing to a safe place in my case. However, I will probably 3D print a small enclosure at a later point and use that for extra safety.

thanx for that video some good information there! I will definitely do this mod when im done with all the overclocking and ready to close the case.

This is what I have done as a temporary solution for now

I see blue corrosion on the keyboard DIN. If that were my board, I would desolder it and plop it into a jar of vinegar, shake it around, let it sit for some time. Rinse it off with water, let it dry, then rinse it with electrical contact cleaner. I would then set it aside and grab a corrosion-free KBC DIN from a dead board. If no dead boards to pillage from, then I'd re-use your once-corroded KBC DIN. It might also be worth while to remove that DIP chip in the socket near the KBC. Very often those fill up with blue corrosion as well which is not immediately visible unless the chip is removed.

There is also a via which is all blued. You'll want to clean that out with vinegar and a solid core wire, used like dental floss. If not, the blue will only spread faster.

ahh yes the keyboard din I have been putting this one off and off but yeah eventually will have to do it.

as for the via blue corrosion you are right, I never noticed it, its funny how you actually notice these things better on pictures then real life, probaby because of slight zoom.
Also good tip about the chip next to the kbd din I will also take it off have a look under.

Also I know I asked this before and got no response but I am very curious would anybody have any guesses what those modifications are on the second last picture of the original post? I think it might be cache or memory chips that its under.
not much info I can find on google for the chips sn74f244n
something to do with memory buffer or cache

actually zooming in it looks like there is a solder iron or some heat burn to some traces so that is probably a repair done for the damaged traces