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Computrend Contaq 386 motherboard

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uncleseth

Experienced Member
Joined
Sep 14, 2008
Messages
50
Location
KY
Hi,

Is anybody familiar with this motherboard (Contaq 386)? I am having problems with it recognizing more than 4MB of memory. I've tried everything possible but still have no luck. Also, I am running 386DX-33 and 387DX-33 chips and it shows the CPU clock at 40. I tried using a 386DX-25 and still the same thing. I do not know if I have the jumpers configured right for the bus clock. I do not understand what all that means.

Thanks,
 
I can see details of that motherboard at http://stason.org/TULARC/pc/motherboards/C/COMPUTREND-SYSTEMS-INC-486-CONTAQ-386.html.

That last table, titled "CPU BUS CLOCK CONFIGURATION" has to be titled wrong. Boards that offer a fixed frequency of 7.2 Mhz (it is usually described as 7.159) use that in the context of the expansion bus (where the cards plug in). And so my thoughts are:

CPU Clock

Like a lot of 386 boards, the CPU is clocked at half the oscillator speed. For example, if the CPU supplied on the board is a 386DX-33, we would expect the oscillator (the 'tin can' next to JP5 and JP6) to be a 66 Mhz one.

Expansion Bus Clock

JP3, JP4 and JP6 (the last table) determine the frequency of the expansion bus. CLK will be the clock that the CPU gets (which is half of the oscillator speed). CLK2 will be half of CLK. Therefore, if the oscillator speed is 66 Mhz:
CLK2/4 = 33/4 = 8.25 Mhz
CLK2/6 = 33/6 = 5.5 Mhz
CLK2/8 = 33/8 = 4.125 Mhz

Those jumpers need to be set so that the expansion bus runs at about 8 Mhz (or less if you have an expansion card that you know isn't stable at that speed).

uncleseth said:
... and it shows the CPU clock at 40.
Click to expand...
What is "it"?
 
Thanks. That cleared a lot of things up. I looked at the oscillator and it shows 80.00 mhz. With the jumpers, I can select CLK2/10, CLK2/8, CLK2/6, CLK2/4 or a fixed 7.2. The board is stable except at CLK2/4 which I believe is running the bus at 10mhz. I have tried all of the above settings but it stills shows the CPU clock at 40mhz. I guess it doesn't matter as long as everything is working. Now if I can get the memory issue figured out I'll be just fine.

Thanks,
 
uncleseth said:
Thanks. That cleared a lot of things up. I looked at the oscillator and it shows 80.00 mhz. With the jumpers, I can select CLK2/10, CLK2/8, CLK2/6, CLK2/4 or a fixed 7.2. The board is stable except at CLK2/4 which I believe is running the bus at 10mhz. I have tried all of the above settings but it stills shows the CPU clock at 40mhz. I guess it doesn't matter as long as everything is working. Now if I can get the memory issue figured out I'll be just fine.

Thanks,
Click to expand...

Well, good for you! You have an "overclocked" computer, and didn't know it. :p You might want to look around for a 40MHz 386 CPU just in case, because this *might* be contributing to your problem. ( the running of the CPU faster than it was designed ). Or, you could insert a 66.666 oscillator for the DX-33, or a 50.0 for the DX25 CPU. The oscillator is what determines how fast your CPU will run ( or try to ), not the speed of the CPU. It's not like the "good new days" where all you have to do is insert the CPU, and it is (usually) autodetected. For that matter, you could insert a 32 or 40MHz can, and run the present CPU underclocked. ( I once *made* a 33MHz Pentium :mrgreen:)

What speed is your ram? Take a look and see if you are at least running 80ns,or preferably 70ns ram. If you have 100ns, or mixed speed ram, that could also be part of the problem.

Back the bus speed down to 7.2 or 8MHz until you get this figured out also.

You sure the board is good ? Pull out all the expansion cards except for the video until you get it running, that might help. You don't need a serial card, floppy or HDD controller to boot.

bobwatts
EartH
 
Any idea on where to get an oscillator? I found an old motherboard with a 66.66mhz oscillator but it is soldered in. The one I have now is held in by a tye wrap( it just plugs in a socket). I am running the bus at 7.2 now. I bought the board off of ebay. There are still some left if you want to check it out. Type in Contaq 386 and it should show it from weirdstuff-inc. I bought some new simm chips online, all 4MB 9chip 80ns for a total of 32MB. I'll try them and see what happens. The board has a 30day money back return so I might be OK after all. I'll try all your suggestions and see what happens while I'm waiting to get my memory.

Thanks,

Seth
 
Oscillators

Oscillators

Hello !

Yes, you can still get them at Jameco.

http://www.jameco.com/webapp/wcs/st... Components / Frequency Control / Oscillators

Don't know how well that will work, I pasted a link to the page of oscillators, but it might not work too well ( now that I see it. )

Jameco.com

or, you can scavenge them from old motherboards, the ones that are socketed. You *can* remove the soldered on one that you found, but this takes some caution, and you would have to clean the legs off. Note that there is only ONE direction to install a clock crystal. Watch the dot. :D

bobwatts
EartH
 
I found on Ebay a 50.000mhz oscillator part number HYBRIDS HT1100. It is a 4 pin rectangular like what I have. Does anybody know if this will work? Does anybody know any direct replacements for the Koyo KCO-120S oscillator? I also found a 66.667 mhz part number Comclock 9234. I guess what I have is called full can due to the fact that is rectangle. Half can I assume is square. Just by looking at pictures that is what I came up with.

Thanks,
 
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Thank you very much for your help. I couldn't have done it without you.

Thanks again,


Seth
 
Thanks for the offer but I just spent $10 on EBAY and got ten of them (had to buy all). I put in a 50.00mhz that I got and left in the DX33 CPU. The memory problem is still there. Hopefully my new memory will fix that. I am though getting new and random errors since I swapped the oscillator. Parity errors and CMOS memory size mismatch and lower 64K errors. Sounds like I've got flaky RAM installed. If the new doesn't work I'll try and swap the board for another. Thanks for everybody's help. I am sure I'll have more questions so please check back if possible.

Thanks,

Seth
 
Heh! Just posted one in the 'available' section. What flavor of RAM are you using? I have some 9-chip, 70ns, 4Mb, 30-pin SIMMs too (known good, tested yesterday in a 33MHz SX).

--T
 
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I just installed my new memory that I got from MemoryTen.com. I have 4 Samsung 4MB x9 chip 80ns and 4 mixed/matched 4MB x9 chip 80ns. I tried the 4 alike in bank 0 and the motherboard recognized the 16MB. I put the other 4 in bank 1 and they were not recognized. I took out the 4 Samsung and installed the other 4 in bank 0 and they were recognized. Sounds like the motherboard has an issue with anything that is put in bank 1. I guess I'll go back and try to haggle with the person I bought it from and try for a replacement unless anybody has any suggestions.

Thanks,
 
Just got another motherboard today that is the exact same. I tried all 32MB of 9 pin 70ns SIMM chips and still the same result. Only 16MB is recognized. I've been all through the owner's manual looking for something I missed but nothing is there. It should auto calculate the memory. The manual says that it should handle 32MB of SIMM memory. Anybody have some ideas? Would anybody be willing to look through my manual if I could get it out on the web somehow? Maybe I'm asking too much for this to work. I don't know of and don't have any programs that really require that much memory. It would just be nice to figure this thing out.

Thanks everyone,
 
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