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8087 is no longer working in NuXT v2.0 motherboard

J

jasa1063

Experienced Member
Joined
Jan 5, 2015
Messages
386
Location
Minnesota, USA
I bought a NuXT v2.0 motherboard back in April 2020. It has worked with no issues since I have gotten it. All of the sudden the 8087 math coprocessor is not working. It is as if it is not even plugged into the socket. Now I now the 8087 itself is Ok, since I have tried it in another computer and it works just fine. I also tried an 2nd know working 8087 have gotten the same result. I even forced the BIOS equipment flag to indicate an 8087 is installed, but no software can detect it. Any ideas what would have gone wrong with the motherboard to cause such an issue. I messaged Monotech PC, the maker of the motherboard, but I have not heard anything back yet. Any insights would be greatly appreciated.
 
Perhaps corrosion on a pin? A different socket would fit differently so it might work elsewhere.

Have you used an ohm meter to verify contact between the chip legs an the bottom of the socket?
 
SomeGuy said:
Perhaps corrosion on a pin? A different socket would fit differently so it might work elsewhere.

Have you used an ohm meter to verify contact between the chip legs an the bottom of the socket?
Click to expand...
The board is only 3 years old and was brand new when I bought it. I did not see any signs of corrosion. I did spray some DeOxit on the socket, but that did not help. I have not gotten out my Multimeter yet to do any further testing, but I guess that is going to have to be my next step.
 
I know very little about the 8087. But if I look at the circuit diagram of the IBM PC, I see three signals running between the 8088 and the 8087. Those signals go nowhere else.

QS0
QS1
RQ/GT

Maybe on your NuXT v2.0, try re-seating the V20.
 
modem7 said:
I know very little about the 8087. But if I look at the circuit diagram of the IBM PC, I see three signals running between the 8088 and the 8087. Those signals go nowhere else.

QS0
QS1
RQ/GT

Maybe on your NuXT v2.0, try re-seating the V20.
Click to expand...
I re-seated both chips, but no luck.
 
Basically, the 8087 runs in parallel with 8088 and uses the 8088 to perform storage operations.
On 5150 and 5160s, there's a switch that indicates whether or not you're using the 8087. If it's not set to NDP enabled, the BIOS will not indicate that it's there.
 
Well it turned to be the NEC V20. Monotech PC suggested I try a different CPU. I tested with both an 8088 and the replacement V20 and everything is now working. I would not have guessed that to be the issue, especially with it working with everything else. I am just glad the issue is resolved.
 
Have you contacted Jacob of Monotech PCs directly about this issue? I'm sure he'd help you out. Nice chap. i've met him in person a number of times.
 
Caluser2000 said:
Have you contacted Jacob of Monotech PCs directly about this issue? I'm sure he'd help you out. Nice chap. i've met him in person a number of times.
Click to expand...
Yes, he was very helpful. He is the one who suggested to try a different CPU and that resolved the issue. He even offered to repair or replace the board if it was faulty even though I purchased 3 and half years ago.
 
I'm glad that the issue is resolved. I have two NuXT PC's, one with 8088 and the other with NEC V20, and they both paired with 8087 FPU's.
I can confirm that NEC V20 is working properly with 8087.

It is strange though that your faulty V20 is working fine without the FPU installed.
Can you checked if it is working together with 8087 on another machine?

Jacob of Monotech PC is such a nice person. When I bought my second NuXT board, I ordered it without 8087, but when I received it, I've notice that it has 8087 installed together with the CPU.
 
rastepanyan said:
I'm glad that the issue is resolved. I have two NuXT PC's, one with 8088 and the other with NEC V20, and they both paired with 8087 FPU's.
I can confirm that NEC V20 is working properly with 8087.

It is strange though that your faulty V20 is working fine without the FPU installed.
Can you checked if it is working together with 8087 on another machine?

Jacob of Monotech PC is such a nice person. When I bought my second NuXT board, I ordered it without 8087, but when I received it, I've notice that it has 8087 installed together with the CPU.
Click to expand...
The V20 does not with an 8087 in two other class computers I have. I think I know what may have happened though. I purchased EGA video card a few months ago and it turned out to have blown Tantalum capacitor that was shorting out the motherboard and would shut down right away. I think the CPU may have gotten damage as a result. Thankfully everything else is in good working order.
 
I wish you to not have any other issues with the machine.
Actually, you could try SVM.EXE or SVM89.EXE utilities which can transform your Trident 9000i to a EGA or CGA card with good compatibility and will keep the computer brand new.
 
rastepanyan said:
I wish you to not have any other issues with the machine.
Actually, you could try SVM.EXE or SVM89.EXE utilities which can transform your Trident 9000i to a EGA or CGA card with good compatibility and will keep the computer brand new.
Click to expand...
Thanks, I have since switched back to the onboard Trident 9000i VGA. Learned my lesson the hard way!
 
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