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Replacing 486DX by 486DX4

Posted on 1999-01-25
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Last Modified: 2008-02-01
I replaced a 486DX by 486DX4...
Changing Power Supply to 3Volts etc.

Now I have problem with Virtual Memory Manager vxd in W95
unless I disable the internal cache (making the DX4 worthless) !

Is there some hope ?
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Question by:PhL
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34 Comments
 
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Expert Comment

by:rmarotta
ID: 1138118
PhL,
Do you have documentation for the motherboard?  If not, post the model number here and we might locate some info on the web.

The first thing you need to do is be sure all jumpers are set correctly on the motherboard for your DX4 processor.  There should be jumpers on the motherboard to set the voltage regulator for the CPU.  If you're using a 3v CPU and supplying 5v, it won't work for long........

It sounds like memory timings could be set incorrectly in the BIOS.  Enter your CMOS setup to enable default values, save & exit.

Let me know how it goes.
Regards,
Ralph
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Expert Comment

by:jhance
ID: 1138119
You realize that there are two different "DX4" CPUs.  One was sold to OEMs and has no heat sink on it and uses a 3.3V power supply.  The other was sold as an upgrade through the retail channel and has a rather large built in heat sink AND a 5V to 3.3V voltage regulator circuit.

First, be sure of which one you have.  The 5V "heatsink" chip will not work at 3.3V so you need to be sure to feed it 5V.  The 3.3V chip won't last very long at 5V so be sure you get the right setting.  

Another problem is that many 486 motherboards were designed/built BEFORE The DX4 spec was finalized and so there are many of them that just don't work with the DX4 chip.  The main area of incompatibility is the CACHE management and from the description of your problem, the motherboard you have may not be compatible.  A BIOS upgrade cannot (usually) fix this problem as it involved the hardware timing and is a problem in the chipset.

One clue to this is the name used in your MB manual for the DX4. If it's actually called the DX4, then chances are good that it is supported.  If it's called by a Pxx (I think it was P24) code name then chances are good that it's not ever going to work unless you disable the cache.


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Expert Comment

by:rmarotta
ID: 1138120
PhL,
All the AMD models I've seen use 3v, but I think there's another model.  Intel made a 5v DX4 without a heatsink attached, in addition to the overdrive models. (it needs one in use, though) It uses 33Mhz clock speed.  I can't say about the cache, but I thought it was a "drop-in" replacement for early DX & DX-2 CPUs.

Which one do you have?

Have you reset the BIOS to default settings?

Ralph
0
 

Author Comment

by:PhL
ID: 1138121
Thanks,

I have a 3.3V DX4 that I had to put a cooler on it !

I have the DOC of the board although some jumpers
are not documented and no apparent Trade Name exists.

Moreover the board should deal with lots of CPUs
iDX, iDX2, iDX-S, iDX4-S iP24D, iP24T, IBM, Cyrix
AMD Dx/DX2 Enhanced or not (etc.)

Disabling External Cache doesn't help
Slowing down DRAM neither
Only disabling Internal Cache works (but SSLLOOWWLLYY)
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Expert Comment

by:rmarotta
ID: 1138122
Installing a "cooler" (fan & heatsink) is necessary on the DX4, but it won't help if you are supplying a 3v CPU with 5v.
Ralph
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Author Comment

by:PhL
ID: 1138123
Motherboard has 4 jumpers to select between 3.3, 4 and 5 Volts !
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Expert Comment

by:rmarotta
ID: 1138124
Bad CPU?
Try another.
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Author Comment

by:PhL
ID: 1138125
The answer is possibly the best one but it seems comments
stop as soon as a question is Locked...

So jhance feel free to comment or reanswer !

Is there DX4-S with two different cache size ?
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Expert Comment

by:rmarotta
ID: 1138126
Have you tried setting the board jumpers for 3.3v and slowing the clock down?

What is the model number of your motherboard?

Ralph
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Author Comment

by:PhL
ID: 1138127
No name, no number already in 3.3V I will try 25MHz...

PCI board with a lot of jumpers allowing for a lot of CPU
(see above).  Not knowing the differences between processors
trying other jumper settings can be hazardous ?

What is the diffrence between Intel DX2-S and Intel DX4-S
or between Enhanced AMD DX4 and Intel DX4-S

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Author Comment

by:PhL
ID: 1138128
It seems to work at 25MHz !

Is there so many DX4 that work at 33MHz but the cache ?
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Expert Comment

by:rmarotta
ID: 1138129
Since you said it is a PCI board, I'll to take a shot.....
The board may be made by several vendors, but see if the following page describes it.  Lots of good info & links there.

http://user.aol.com/sdnd/vip.htm

Regards,
Ralph
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Author Comment

by:PhL
ID: 1138130
Adjusted points to 150
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Author Comment

by:PhL
ID: 1138131
The board is nearly the same but NO Vesa slot !
By the way I was not able to locate CacheCheck...

Regards,
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Expert Comment

by:rmarotta
ID: 1138132
Try this site:

http://www.sysopt.com/cachk4.html

Ralph
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Expert Comment

by:CletusS
ID: 1138133
PhL
If we had the motherboard type, we could surely make more progress.  If you can give us the 'ID string' from your bios.
If you are not familiar with that.  It is the long string of numbers and letters that your bios spits out(usually at the bottom left of your screen when you turn it on). This will help us determin the manufacturer of your motherboard.

this is an example from an AWARD bios, though they all are simular.

i430tx-NS309-2A59IQ1GC-00
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Author Comment

by:PhL
ID: 1138134
Here it is but I already know that HSING (PCCHIPS.COM ?)
should have made the board.
Chipset is ALi 1487/9 :

AMIBIOS 94 release 7/21/95
# 41-A300-001437-00101111-101094-21011/33-E

Cachecheck is nice but doesn't test the memory or cache
for faults...

In summary it works at 100MHz without Interna Cache
                    at  75MHz with Internal Cache
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Expert Comment

by:rmarotta
ID: 1138135
PhL,
Is this your board? :

http://www.pcchips.com/m918.html
http://www.pcchips.com/m918jp.html  (for jumper settings)

DX-4 is supported.  Check for correct jumper settings.
After that, if the cache RAM is socketed, (I can't tell from the pix), I'd try some new or faster chips.

Regards,
Ralph
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Author Comment

by:PhL
ID: 1138136
That is the good one !
Unfortunatelly the jumpers are the exact copy of the
user manual I had !

How can the external cache have some effect ?
I have the problem if Internal Cache is enabled
with External Cache either Enabled or Disabled...

Also I always thought that the Speed outisde the processor
was the same for DX33 and DX4-100.  And all was nice with
the DX33 !

Thanks again I will try to download the new BIOS...

Regards,
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Expert Comment

by:rmarotta
ID: 1138137
Oops.  I had external cache on my mind.  Disregard that comment.

The jumper settings at the website showed configuration for the DX-4.
Did your book?

If the BIOS update won't get it going, (doubtful) I think you need another CPU.

Let me know.....
Ralph
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Author Comment

by:PhL
ID: 1138138
I used the DX-4 jumper setting although I'm not sure what
should happen if I used another one...

Still unable to FTP pcchips (too many users !)
Still no software to test memory (not size but correctness) !

Ralph, don't you think to lock the answer ?

Thanks for all,
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Author Comment

by:PhL
ID: 1138139
I changed the BIOS !
It solved a Invalid Page Fault I had with a 32-bit .DLL

Unfortunatelly nothing changed about using Internal Cache
at 100 MHz...
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Accepted Solution

by:
rmarotta earned 200 total points
ID: 1138140
Phl,

It seems you have gone as far as possible with the present setup.  At this point I think your answer lies in changing the CPU.
At any rate, you have gained some improvement by running at 75Mhz.
Good luck with it.

Ralph
0
 

Author Comment

by:PhL
ID: 1138141
I would like to test memory.  Even at 75MHz something may
go wrong once every day...
If I got another CPU that seems to work I would like to check it!

Any freeware for doing such a testing ?

Thanks

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Expert Comment

by:rmarotta
ID: 1138142
Go here to download a demo of AMIDIAG:

http://ami.com/utilities/main_utility.html

A good all-around system checking utility.

Ralph
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Author Comment

by:PhL
ID: 1138143
Sorry no MEMORY Test in the Demo...
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Expert Comment

by:rmarotta
ID: 1138144
Sorry PhL.  I have used that utility a long time ago, and it had a good memory exerciser.  So, I went there and downloaded this demo, thinking I'd upgrade, only to find that most of it is disabled.

I'll find another......

Ralph
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Author Comment

by:PhL
ID: 1138145
Did you find ?
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Expert Comment

by:rmarotta
ID: 1138146
I haven't found anything other than cachcheck for the memory.

Here's a link for info and download of a free diagnostic that will check the entire system, including memory:

http://www.tufftest.com/tt01-lite-dwnld.htm

Be sure to browse the site to read about it, and then try it out.
I hope it helps.
Regards,
Ralph
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Author Comment

by:PhL
ID: 1138147
Got it !

Unfortunatelly nothing is wrong with the BAD processor at
100 MHz ?

So what is the special thing that W95 is doing ?
Mostly when graying the screen after asking for Shutdown ?

Regards,

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Author Comment

by:PhL
ID: 1138148
Worst now !
I used a TSTRAM of mine putting a 286 in protected mode...
Although I got it work on a PentiumPRO without problem
with THE ABOVE machine he just reboot the PC destroying
the all content of the Hard Drive !

Reinstalling W95 now !
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Expert Comment

by:rmarotta
ID: 1138149
You've lost me now.......
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Author Comment

by:PhL
ID: 1138150
I just said the Memory testing I got is to kind to produce
any error although W95 manages to do it !
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Author Comment

by:PhL
ID: 1138151
Thanks !
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