• Please review our updated Terms and Rules here

Help identify 286 motherboard

H

Henrik Wils

Member
Joined
Nov 12, 2013
Messages
12
Location
Vallensbæk, Denmark
I just bought this 286 motherboard brand new. However, it didn't come with a manual, and it's really hard to find anything printed on the board, that gives a clue about what it is. I don't have a lot of experience with 286 motherboards.

286big.jpg


I noticed that the chips are running 12.5mhz, but the CPU is just 10mhz. Seems a little odd to me, but I guess it's possible to upgrade it to a 12.5mhz CPU. But that probably requires some jumpers to be set differently I guess.

Am I right, that this board is equipped with 9 MB RAM? Seems like an odd number of DRAM slots to me - 4x9?

Any information is appreciated.
 
I think you didn't post the pictures.

If the system was late enough to have SIMMs, then it was almost certain that the 286 would have been capable of 16MHz but sold at lower prices as a 10 or 12 MHz. Find the oscillator and divide its speed in half. 25MHZ oscillator and everything will run at 12.5MHz. To run the system at 10 MHz, you need a 20MHz oscillator. The assembler might have saved a little by running the 286 faster than the printed speed.

4x9 for RAM chips is a common setup for a 286 and usually means only 1MB on board (with 256 kbit chips) though a few took 1 Megabit chips for a total of 4 MB. 9 chips for 8 bit byte and 1 parity bit. If it has 9 SIMM slots that would be an unusual setup and I really want to see pictures.
 
If you can plug a power supply and a video card, the BIOS ID string shown in POST screen would be helpful.
 
Oh right, it's in bits, not bytes of course.

Seems like I can add the motherboard to the list, if I ever find out what it is. I couldn't find anything that looks like it on that site. Almost all other boards that comes close, has memory on top and cpu's on the bottom or near the keyboard connector.

I tried to power it with a Prisma VGART 800 ISA display adapter - That's the only ISA I have. I got no picture and no keyboard lights, but the CPU is getting hot, so something is going on.

I did cut off the CMOS battery, as it was leaking, so it's running without any batteries right now, but that shouldn't stop the BIOS from booting, should it?

I don't have any controllers attached, but then again, that shouldn't be required for bootup, right?
 
PhilipA said:
I don't see anything in TULARC that matches it. Does it have an FCC ID on it anywhere?
Click to expand...

No. The back side says "Made In Taiwan" and the number 8841 with an LCD-like font.

back.jpg

Does anyone have an idea how I can determine the PC speaker pins? If it's 4-pins, it could be J2 (at the keyboard connector), J11 (near the chipset) or J7 or J20 (on the other side of the chipset, near the crystals).

I actually noticed that the main crystal (24.000 Mhz) has a small dent. Is that a problem? It's socketed, so it would be easy to replace.

How many post do I need to make, until approval is no longer necessary?
 
Henrik Wils said:
Does anyone have an idea how I can determine the PC speaker pins? If it's 4-pins, it could be J2 (at the keyboard connector), J11 (near the chipset) or J7 or J20 (on the other side of the chipset, near the crystals).
Click to expand...
Considering its location, I think J2 is likely to be for an external battery.
 
I think I will try a buzzer on J20 tonight.

I'm still wondering about the bus speed. All the "CHIPS" are marked 12.5Mhz, and the crystal (which is easily replaceable in a socket) is marked 24Mhz, yet the cpu is 10Mhz. Does that sound right?
 
Henrik Wils said:
I did cut off the CMOS battery, as it was leaking, so it's running without any batteries right now, but that shouldn't stop the BIOS from booting, should it?
Click to expand...
Henrik Wils said:
I don't have any controllers attached, but then again, that shouldn't be required for bootup, right?
Click to expand...
On a generic 286 motherboard, I would be surprised if a lack of battery or FDD/HDD controller stopped startup.

Henrik Wils said:
I actually noticed that the main crystal (24.000 Mhz) has a small dent. Is that a problem? It's socketed, so it would be easy to replace.
Click to expand...
I do not think that anyone here could say with any certainty that a dent would either cause or not cause a problem to an oscillator module.

Henrik Wils said:
How many post do I need to make, until approval is no longer necessary?
Click to expand...
Probably something that the moderators would not want public.

Have you tried a POST card?
 
Agreed, J2 is for an external CMOS battery.

I'd put J10 as the power light/keylock terminal, J11 probably the speaker.

Depends how deep the dent is in the crystal case. Easiest way to see if it's working is to apply power and check with an oscilloscope or frequency counter.

--Phil
 
No sound from J7, J11 or J20.

I've ordered a PC analyser card to see how far it goes.

I did however, notice that they all keyboard LEDS light up immediately when power is switched on, but they don't react to lock keys. But I guess keyboard is one of the last things to be initialised by POST, and it's probably hanging before that.
 
I have now reseated all chips on the board (including all the LPCC socketed), and replaced the CPU with a 12 Mhz, and also placed a co-processor rated 8 Mhz. Still no dice :(

When I plug in the PC analyzer, all leds but IRDY light up, so at least it gets all correct voltages. However, the display reads "-- --" and never proceeds with anything else.

pca.jpg

I have read the manual for my Prisma VGART 800 display adapter, and checked dip switches on it, just to make sure. I can't make out what's on and off on the switch (one end reads OPEN, but does that mean OFF? - In that case, all switches are in the OFF position). However I have tried changing some of those that I believe could make a difference (e.g. forced 8 bit BIOS mode, or Auto Switch).

I noticed that the manual for the video adapter, mentioned that there would be a jumper on the motherboard that tells the BIOS what kind of display adapter is in use - Anyone heard of that before?

Both CPU, coprocessor and several of the "CHIPS" chips become hot when it's on.

I'm at loss at what I can do now to make it work. Maybe try another display card, and maybe try adding a CMOS battery, if that's what it is mad about. I could try looking for somewhat similar motherboards to see if they have jumpers in approx same locations, but that's kinda hit and miss. I could also just try to switch the jumpers around on the motherboard, but then again, who knows what I might mess up?

If you have any ideas as to which jumpers might be worth looking into, that's highly appreciated.
 
Hi Henrik,

Sorry to hear about your troubles. Yes it is frustrating when a board won't POST, had a few myself and they drive you nuts!

Here's a few things come to my mind:

First, plug a PC Speaker into J20 (the two outside pins, 1 and 4)

Try turning it on with NO video card, just the speaker. You SHOULD get some beeps. Sometimes video cards keep boards from posting at all.

Try removing the co-processor, narrow things down.

Bit drastic, maybe the RAM is bad?
Try removing banks 2, 3 and 4 of the DIP RAM, boot up with bank 1.
Next try substituting Bank 1 with the chips from one of the other banks.

Try a different power supply, maybe the "Power Good" signal from the supply is not working.

You mention the keyboard LEDs light up, fo they flash on and off, or do they stay on? If they flash on and off I think that means the board is proceeding through the POST somewhat before stopping, gotten past the keyboard test. If they stay on it just means it's got power, nothing happening.


About the model, I notice a number in the far upper-right of you pic, that could be the number. I had a board that only said "486c-v2" on it, that was it, turned out to be an A-Trend. So any little number you see might be the model, anything on the reverse side?

That's all I can think of for now Henrik, hope this does the trick for you!

Bellarmine
 
Last edited:
It does say PAT-7.2A in the corner and Y-7.2 in the middle, but that's the only thing on the entire board, and Google wasn't of much help with these numbers.

I have already tried to narrow things down, and this time with only BANK 0 full of RAM - First with the NEC ones, then with OKI ones. Didn't change a thing. Also removed co-processor and reverted back to the original 10mhz CPU.

Also tried a few of the different places where a speaker might fit.

I'm pretty sure that J20 is NOT for a speaker, since I determined that pins 1 and 4 are shorted (so are 2 and 3) and neither of the 4 pins has GND. It's more likely J7 or J11, but none of them seems to respond to my speaker. Perhaps I should make sure the speaker still works :)

I did try another PSU, and when I did that, I noticed that the keyboard LED's would blink continuously (this was without display adapter). Could be an error code or maybe simply the board rebooting over and over. It wasn't consistent with this state, and after trying a few things, I was unable to reproduce it again. The first thing I tried, was putting the display adapter, but nothing was shown.

I narrowed down all the GND pins on headers which aren't obviously just jumpers.

286big-gnd.jpg
 
Hi Henrik,

There's another 4-pin J7 which might be for the speaker. Also I notice a bit of corrosion below the battery, maybe make sure everything is clean and there are no broken corroded traces around there.

You could try checking if J2 is connected to the battery connectors, and connect three 1.2V cells to it, maybe it needs a battery to POST. Or connect them to the old battery connectors directly.

Aside from these Henrik, sounds like you've tried just about everything.....:(


I surely don't know everything, other members might have some other ideas, but at this point Henrik I'd throw in the towel. Sometimes motherboards just go 'dud' for no visible reason.

To illustrate, let me cite a particularly weird example that just happened to me a few months ago.

Last year I found a big Dell Xeon server at my dump, booted it up a dozen times worked perfect. I listed it on Kijiji for fun and stored it away. Early this year I got a good offer on it, I got it out and booted it up to make sure it still worked before shipping it. Again worked perfect, turned it on and off a few times, and shut it down for the day.

Next day I turned it on, dead no POST, zero nada. I tried everything, swapped CPU, RAM, unplugged everything, removed the whole board. Whatever I did I NEVER got it to boot up again. It was just working 12hrs before, shutdown one night, next day dead, no changes or anything - really tearing my hair out!

Fortunately it worked out for me, I managed to find a new replacement board on eBay and got it shipped up and installed it while still making a very good profit, was lucky.


Anyway, my point is sometimes they just go bad, probably a tiny component responsible for the board powering up is bad, and good luck finding it. I noticed while I was debugging my Dell board that after a while the Power LED stopped lighting up, probably a clue but who knows, only 100 million parts to check lol. My Dad says all these transistors, which are really crystalline structures, do not like shock. The Dell had gotten thrown, so I guess something was cracked and finally failed. Who knows what your 286 board has bounced through the past 25 years or so, static damage etc etc.....:D


Hope this makes you feel better Henrik, you're not alone......:)

All the best,

Bellarmine
 
You must log in or register to reply here.
Back
Top