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Frankie
June 29th, 2006, 02:23 PM
I have a FX-3000 Rev: 1.0 motherboard with a i486SX-25 CPU installed and no cache memory (Iíll list more details below). Iím trying to downgrade it to a AM386DX-40 CPU. The problem is that the computer detected it as a 16 MHz processor instead of a 40 MHz. I checked all the jumper settings and BIOS and canít find why its running at a low clock speed.

Can anyone suggest anything about this problem?

4 MB
BIOS type: 40-0100-001131-00101111-121291-UMCAUTO-F
Diagram/Jumpers settings: http://www.peteweb.com/ftp/user-submitted/us3486.zip

modem7
June 29th, 2006, 03:21 PM
It is possible that when the manufacturer states, "Supports 80386DX,80487SX/80486SX/DX/DX2 at 25/33/40/50/66MHz', they don't mean all of those CPUS at all those speeds, just particular combinations. I think that's unlikely.

Could be one of those motherboards where setting certain RAM speeds limits available CPU clock speeds (and vice-versa).

NathanAllan
June 29th, 2006, 05:21 PM
iirc, not many of those machines of that era detected much of anything, and you have to set it bios. Can you get to the bios? If you can, look for a setting that you can change. Also, I didn't even know that there was a 40mhz 80386. Look at the actual chip and see what it says. It might say 16mhz.

Nathan

compu_85
June 29th, 2006, 05:32 PM
I've got some Karlnet wireless Brouters that are based on a 40mHz AMD 386.

-Jason

Terry Yager
June 29th, 2006, 07:50 PM
Modem7 may be on the right track with the memory thing. Check the settings and try some tweaking. Also, are you using a 387 on the board too? Be sure it is the same speed as the 386. Some boards support asynchronous operation, and some do not. On a board that supports only synchronous, it might kick the CPU speed back to match the NPU.
On my '386 board is a jumper to select between 33MHz & 40, but it's always been flakey when run at 40, so I just keep it set back to 33, although both chips are rated for 40.

--T

NathanAllan
June 29th, 2006, 11:52 PM
I've got some Karlnet wireless Brouters that are based on a 40mHz AMD 386.

-Jason
Ah, I stand corrected. I looked in my little box o' processors and found a 40mhz 386. I guess I said that cause I never had one of those actually inside of one of my machines. It's in the box, though.

mbbrutman
June 30th, 2006, 05:37 AM
I should have spotted that earlier. Intel only went to 33MHz on their 386 class processors. AMD had a 40Mhz.

My workhorse vintage system for programming has one of these with a 128K L2 cache and it is quite competitive with low-end 486s except for the lack of floating point.

Jorg
June 30th, 2006, 06:49 AM
iirc, not many of those machines of that era detected much of anything, and you have to set it bios. Can you get to the bios? If you can, look for a setting that you can change. Also, I didn't even know that there was a 40mhz 80386. Look at the actual chip and see what it says. It might say 16mhz.

Nathan

It won't have a bios/cmos setup, it will have only the jumpers which you have to set the correct bus speed by.

Frankie
June 30th, 2006, 09:09 AM
I donít have a coprocessor installed. This computer does have a BIOS. The information in the zip folder shows that there are no jumper settings to change the clock speed. As for the BIOS, there are no settings to change the clock speed either. I tried changing the memory speed but that had no effect.

CPU type: A80386DX/DXL-40

kb2syd
June 30th, 2006, 12:56 PM
There is probably an undocumented jumper for selecing the speed for a 386 CPU. Are there any on the motherboard that don't appear in the gif image, or that are not documented in the text file?

I found a few "similar" motherbords where J4 would select a 20MHz clock or 16MHz clock for the 386.

Frankie
July 1st, 2006, 11:50 AM
No, in fact it matches the motherboard very well.

Frankie
July 2nd, 2006, 12:42 PM
I think I found the problem. After doing a through look of the motherboard I found a crystal oscillator. I didn't think much of it at first, but when I tested a i486DX2-66 processor yesterday, the computer detected a clock speed of 50 MHz, the original was a i486SX-25. When I checked the crystal, its was rated at 25 MHz. Also it's socket, not soldered.

If I replace it with a 40 Mhz crystal, will it fix the problem?

Terry Yager
July 2nd, 2006, 01:09 PM
If I replace it with a 40 Mhz crystal, will it fix the problem?

Might work, as long as all the other components can keep up with the extra speed. Oscillators are cheap, so it's probably worth a try (at your own risk, of course, keeping in mind that it might fry sum'n). I would imagine that the crystal is socketed for a reason...

--T

modem7
July 3rd, 2006, 05:49 AM
If you do web search, you'll see lots of code showing how to determine the make/model of your 386/486 (e.g. "AMD 486 DX/4").
This is done principally by the use of the CPUID instruction, but on some CPU's (that don't support the CPUID instruction), the presence/absence of certain bugs/features is used.

With the 386/486, the only way you could tell what the rated speed of the CPU was, was to look at what was stamped on the CPU.
As far as speed was concerned, utilities of the time simply gave you benchmark figures (e.g. your CPU is running at the same speed as a 386-20).

And so with the BIOS/POST on 386/486 motherboards not being able to determine the rated speed of the CPU, it is up to the user to configure the motherboard to deliver the correct/desired clock speed to the CPU. That has to be done via jumpers, switches or via the BIOS setup.

Yes, it's odd that the crystal is socketed, but I think it's even more odd that a motherboard manufacturer would produce a motherboard where a PC builder would need to change crystals in order to accommodate all of the supported CPU's ("Supports 80386DX,80487SX/80486SX/DX/DX2 at 25/33/40/50/66MHz").

Could this be one of those motherboards with a hidden BIOS setup screen (i.e. once in the BIOS setup, a special key sequence is then used to access the 'advanced' BIOS settings)? I came across one of these many moons ago but I can't remember the details.

Terry Yager
July 3rd, 2006, 07:03 AM
Is it an AMI BIOS? (I don't recall if you mentioned it before).

--T

Frankie
July 3rd, 2006, 08:10 AM
Is it an AMI BIOS? (I don't recall if you mentioned it before).

--T
Yes, its a AMI BIOS.

modem7
July 4th, 2006, 02:38 AM
http://www.uktsupport.co.uk/acer/faq/acer.htm shows that on some Acer models, the 'advanced' section is hidden.

Also from the Net: "I have Award BIOS ... On my system, Ctrl-F1 while on the main page of the CMOS setup program will un-hide some hidden menus, but it was in the manual."

And so hidden menus in the setup is still a possibility. You mentioned that you tried changing the RAM speed. As the diagram/text you supplied shows no jumpers to do that, you must have done that via the setup. If so, it doesn't make sense to me that a manufacturer (/BIOS programmer) would put RAM speed in the 'standard' section of the setup and then put CPU clock speed (something of similiar complexity to a user) in the 'hidden' section. Still worth looking into. You have an AMI/Award BIOS - try "Ctrl-F1 while on the main page of the CMOS setup".

By the way. You were unsure of the motherboard manufacturer. There's a website that identifies AMI BIOS "40-0100-001131-00101111-121291-UMCAUTO-F" as being used by the 'Elitegroup FX3000' motherboard.
That ties in with the diagram/text for a US3486 motherboard that you supplied - also made by Elitegroup.

Frankie
July 5th, 2006, 12:14 AM
I know FX-3000 is my motherboard, it's just when I did a web search, it brought me here: http://www.peteweb.com/index.php?showtopic=3984 (look at "Specific Models"). The jumpers matched perfectly with the text and diagram. The only thing different is the local bus, there are holes where it should be.

As for the hidden BIOS options, I could not find any. However, I did find this program http://fresh.t-systems-sfr.com/pc/src/misc/old/amis2990.zip/ which did allow me to access hidden options, but none of them were useful to my problem..

modem7
July 5th, 2006, 02:23 AM
Elitegroup obviously released the FX-300 and US3486 about the same time.

I think you're at the point where you need to locate the user manual, either for the FX-3000 or for the US3486.

Frankie
July 8th, 2006, 03:33 PM
I changed the crystal with one rated at 40 MHz. The computer started up with no problems but its still not detecting the right speed. It did detect a different speed; right now it sees it as a 20 MHz processor instead of 16. The computer does feel faster. I used a program that detects CPU IDs but it didn't work (“N/A”).

Like I said, it did detect a new speed and does feel faster. Could it be that the computer needed a 20 MHz crystal instead? If someone on this forum has a motherboard with an AM386DX-40 CPU, it would help if you can give me the rating on your crystal so I can verify this (look below if you don't know what it looks like)..


As far as speed was concerned, utilities of the time simply gave you benchmark figures (e.g. your CPU is running at the same speed as a 386-20).
I would like to use a utility like that to test my CPU (just in case its a BIOS error).

Terry Yager
July 8th, 2006, 03:53 PM
Sounds like it might be a divide-by-two circuit, in which case, you'll want an 80MHz crystal.
<rummages around...digs thru pile of dead parts>...Aha! Here 'tiz...
Ok, FWIW, I'm looking right at an old board here, and it has a 40MHz 386 DX chip installed, and the crystal is a 66MHz. I've never seen this board running, so I can't swear to what speed it actually ran at. As always, YMMV.

--T

Terry Yager
July 8th, 2006, 04:08 PM
Yeah, that makes sense. The original was a 25MHz crystal and a 486 DX/2, which actually 'ran at' 50MHz, correct? The 486 DX/2 is a 'clock-doubler', so on a 25MHz clock it would (apparently) 'run at' 50MHz. Going back to a 386 chip makes it run at half the speed of the oscillator. (And the board I have prob'ly only went up to 33MHz, even though the CPU is rated for 40).

--T

Frankie
July 8th, 2006, 04:47 PM
Actually, the original processor was a i486SX-25, I just tested the 486DX2-66 to see what would happen. I do see what you are saying thou.

modem7
July 8th, 2006, 04:55 PM
I would like to use a utility like that to test my CPU (just in case its a BIOS error).
Try early versions of Checkit and Norton Utilities.
An early version of CheckIt is at http://members.dodo.com.au/~iamextinct/

Frankie
July 8th, 2006, 06:26 PM
CheckIt results show that the computer is indeed running at 20 MHz.

Going back to a 386 chip makes it run at half the speed of the oscillator. (And the board I have prob'ly only went up to 33MHz, even though the CPU is rated for 40).

--T
So your saying If I replace the crystal with a 80 MHz (if I can find one), that will fix the problem?

Terry Yager
July 8th, 2006, 06:45 PM
Best guess, mebbe. I have seen 80MHz crystals on boards of that vintage before. Then again, there's mine, which I mentioned earlier in this thread. It's *s'pozedta* be able to run at 40MHz, but it's not reliable at that speed, so no guarantees.

--T

Terry Yager
July 8th, 2006, 06:49 PM
When I dig my '386 out for a couple of other projects (tomorrow, Chris...really!), I'll open 'er up and confirm the speed of the oscillator, if I can.

--T

modem7
July 9th, 2006, 02:44 AM
I have located a 386DX-40 machine. It has a socketed 80Mhz crystal (secured with a cable tie).
The motherboard is an Elitegroup UM386 - same manufacturer and from around the same time.
Based on that info, I think that there's a very good chance that an 80Mhz crystal is your answer.

modem7
July 10th, 2006, 04:37 AM
Found another 386DX-40 machine.
OPTI-391 motherboard (has CPU soldered onto motherboard).
Crystal = 80 Mhz

Terry Yager
July 10th, 2006, 09:12 AM
Found another 386DX-40 machine.
OPTI-391 motherboard (has CPU soldered onto motherboard).
Crystal = 80 Mhz

That pretty much settles it then. Now I don't hafta open mine up, I'll prolly just find the same thing.

--T

Frankie
July 11th, 2006, 10:03 AM
Well, I know what I have to do; the problem is where do I find the 80MHz crystal? There is one on ebay, but he's selling them in quantities of 20. And the store where I knew I could find the crystal at, closed..

modem7
July 12th, 2006, 01:56 AM
The crystal on my EliteGroup motherboard has a part number of: KDN-110S 80.000 Mhz
The crystal on my other 386DX-40 motherboard has a part number of: KDN-020C 80.000 Mhz

They look physically the same to me - perhaps an electrical difference.
Google with "KDN-110S" and "KDN-020C" shows lots of hits.

As the your EliteGroup 3000 motherboard is 'closest' to my EliteGroup motherboard, I'd put preference in the 'KDN-110S 80.000 Mhz' version.

DimensionDude
July 12th, 2006, 11:32 AM
They look physically the same to me - perhaps an electrical difference.
Google with "KDN-110S" and "KDN-020C" shows lots of hits..


My educated guess...perhaps one is for a series tank circuit, the other for parallel. Or, a difference in the cut (X,Y) of the crystal.

Kent

modem7
July 13th, 2006, 01:50 AM
When the 'tin can' has only two leads, the can only contains a crystal.
These 4 pin cans contain extra components to create a self-contained oscillator. You supply 5 volts (or whatever) across two pins and you get an oscillating signal out of the other two pins.
And so maybe the difference in part numbers is the supply voltage, or the accuracy of the output, ....

Unknown_K
July 14th, 2006, 11:42 AM
There are more complex oscillators also:

http://www.brookdale.com/champion/k1601.htm

4 leg with a trim pot

I need to find a replacement K1602T (24.545454 Mhz) for one of my video capture boards that had all 4 legs broken off in shipment (nothing left to solder onto).