Hi Jed118!

Back in '94 I added a 8087 to my XT clone, I think it didn't get to execute at least one instruction - I had no software that would use it, not even a test program or benchmark, so I guess it qualifies at the most pointless upgrade ever. But I remember it running (idling, better said) very hot. Pretty sure mine was an original one.

More recently I got a 287 from China, and it's an obvious fake. Still, it's detected and seems to be running ok, so yours might too - just run some diagnostics and benchmarks.

About your second chip, if there's non-zero resistance between the two GND pins, I think you will have to provide a GND on pin 20 or what's left of it. Please attach a photo for better suggestions 😀
(Also check if the motherboard is 'providing' GND to pin 20. Maybe it's left floating, in which case you don't need to bother restoring a connection)

Hey Nick,

That's a good idea, I should check the board's FPU socket *edit checked - pins have perfect continuity - looks like I'm soldering on a leg (after midterms, I've clearly procrastinated enough). It was 4AM when I put this away 🤣. Also, this hard drive is loaded with CAD and other programs that look like it would benefit from an FPU. I had a 287 in one of my systems recently - I never thought to touch it or measure the temps.

I went off of an older VWestlife vid where he tests a Chinese FPU against an authentic one, and it seemed to work. I'd love to get a copy of the Intel Advanced Coprocessor test he was using... only one dead link online. I ran some tests on my FPU that I could find online, as well as CheckIt, seemed to pass at the time. I didn't put the 87 test into continuous mode, should have tried that.

I didn't know the FPUs ran hot. I'm still new to XTs, having little exposure to that tech over the decades. This, however, is not normal behaviour:

This wasn't the worst of it - at one point, I issued a DIR command after moving some files around on an extended partition and what listed was not in the 8.3 format at all. Then I lost the partition. All this stopped when I removed the FPU (and repaired the MBR with NDD, which was conveniently on the primary partition).

Here's the FPU - recently bought one on top:

The replacement is missing its pin here (top FPU)

The Chinese one is in the foreground:

I'm not sure what all that discolouration is in the epoxy sandwich - maybe it's gone bad 😦

Bonus pic of something I found on the hard drive, which put a smile on my face:

I put the Chinese FPU back in, within 10 minutes I was having issues with data errors when reading drive c:, random crashes, etc.

So, I soldered a leg to my old 8087 after putting it in the socket (I tried to run it without the leg - no dice) and after 30 mins of stress testing and messing around, no errors. The FPU also runs cooler (by about 5-7 degrees) than the Chinese one.

The seller issued me a refund but wants me to send him pictures of the destroyed chip? Yeah, no, I need something to put back in my shadow box for display, working or not.

Repaired original FPU - you can see I tickled it with a soldering iron on pin 20. It works, not sure about the thermals haha! Still runs pretty hot. Not as hot but still. CPU is cooler as well.

So how does an FPU interfere with diskette and disk I/O, and send garbage onto the screen, exactly?

I am no math processor expert but it seems to me it's connected to many or all of the same data lines as the main processor. If it's defective it may be putting data into the bus when it's not supposed to be?

Intel was the only manufacturer that produced the 8087 in any meaningful quantity. AMD and Cyrix were said the have developed clones, but they are so rare they might as well not even exist. There's also a very rare Soviet clone, which comes in unusual packaging.
To the best of my knowledge, the Chinese never cloned the 8087, so I highly doubt you have a fake (if it works at all). It's probably either defective or overclocked/remarked. I had a similar experience with an 8087-1 that I bought from China. It had markings that indicated it came out of a PC9801 system, but it didn't seem to work correctly at 10MHz and would often crash the system doing mundane things not related to the FPU. That would be normal behaviour if overclocked or defective due to the way the 8087 is interfaced to the 8086.
8087s do indeed get quite hot. They are apparently a lot more complex than the 8086, and Intel never bothered to transition them to CMOS for some reason.

my 8087 is IBM marked, but I guess that's just an Intel part rebranded?

maxtherabbit wrote on 2021-02-23, 18:23:

my 8087 is IBM marked, but I guess that's just an Intel part rebranded?

Yes.

Well, after a day of being on, no hangups. Def. bad FPU. Thanks for the foray into the 8087 😁

I seem to recall an AMD 80287 passing through my hands in the late 90s (I could totally be mistaken) and wanting to hold onto it - I *may* have stuffed it into a friend's dad's old 286 (which he threw out 5-6 years ago, EGA monitor and all... Ouch). As for non-Intel 8087, I've only heard the Cyrix legends.

https://dougx.net/gaming/coproc.html

The old ceramic NPUs draw ~2,5 ampere and get quite hot, I think. Not sure if this a bad thing per se, though.
I'd be worse if the heat produced by these NMOS designs would stay in the casing.
In this context, It's perhaps good that no plastic package was used. 😀

The 8086+8087 combo is/was a true processor/co-processor design.
Each of the CPUs are with equal rights or "worked as one", so to say.
http://www.ray.masmcode.com/tutorial/fpuchap3.htm#FWAIT

To some degree, the 80286+80287 still had a similar relationship (though quite a bit watered down).
Though on a 286 it was possible to "intercept" the processor-co-processors communications.
FPU emulators were able to "hook in" an act like they were a real 80x87.

PS: These are just some random thoughts. 😅 I also think that FPU was broken, btw.

Jed118 wrote on 2021-02-21, 15:08:

I'm not sure what all that discolouration is in the epoxy sandwich - maybe it's gone bad :X […]
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I'm not sure what all that discolouration is in the epoxy sandwich - maybe it's gone bad 😦

Bonus pic of something I found on the hard drive, which put a smile on my face:

Aw, the good old NCC1701! 😎 ..or is it the NCC1701A already ? 😉

Jo22 wrote on 2021-02-24, 16:30:

https://dougx.net/gaming/coproc.html […]
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https://dougx.net/gaming/coproc.html

http://www.ray.masmcode.com/tutorial/fpuchap3.htm#FWAIT

Bonus pic of something I found on the hard drive, which put a smile on my face:

Aw, the good old NCC1701! 😎 ..or is it the NCC1701A already ? 😉

These are amazing resources, I'll have fun reading those. For example, I did not know that the two were paired in such a way, I assumed they worked like the 386 FPUs. Thanks so much for these links!

The FPU was bad. Either that or relabelled as a -1. Either way, it has taken its place of honour (after the reverse being labelled NOT FOR 10MHz) in my display case, likely never to be installed in anything again.

That is the NCC-1701-A - the nacelles have swept back pillars 😁

You're welcome! ^^

Jed118 wrote on 2021-02-25, 01:51:

That is the NCC-1701-A - the nacelles have swept back pillars 😁

Ah, I see. Thanks for pointing that out. ^^ I've been watching TOS, TNG, VOY since I was little, but I'm still learning.
The books/novals of the TOS era, for example.. Really fascintating, IMHO.
(Btw, if you like TNG a bit, check out LCARS 24. It's a really useful Trek UI for DOS/Win..)

PS: I've attached a few utilities for x87. Maybe they are useful to you, too. 😀

I read a few TNG novels as a pre-teen, borrowed from the local library. They were pretty descriptive, I remember wanting to read more. I was a huge (I guess still am?) trekkie, but it comes in bursts these days. I think I still have a couple starship models lying around (not at all painted well, I was...12? 13?) that I kept from that time.

Thanks for those utils - I will throw them on a diskette and try them out. The goal now is to get Win 2.03 running at 800x600 (I did find a driver online) and install a SCSI CDROM and an Adlib (Radlib) clone as I have a Future Domain 8 bit SCSI card and the drivers/cabling for it. Unfortunately the 1x slot loader CDROM doesn't work, but I have a 4X unit that I'll put in.

Why? Because I can 😀 I've also ordered a 2400 internal modem for it for era-correctness.

Sounds cool! Good luck! 😀

Btw, the included Win progs will run on either Win 2.x or Windows 3.0 Real-Mode..

Jed118 wrote on 2021-02-21, 15:08:

Bonus pic of something I found on the hard drive, which put a smile on my face: […]
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Bonus pic of something I found on the hard drive, which put a smile on my face:

Hi again! I don't mean to unbury this old topic, but just a few minutes I found this:
http://www.sabrizain.org/startrek/lcars.html

Windows 2.x was launched in 1987, just two months after TNG had aired (in the US).

The irony is, though, that the Okuda dude was more of a Mac person.
The LCARS panels were made with the latest Mac software back then.

Btw, if you're curious about how the animation was done, have a look at this: Link

Anyway, I don't mean to go off-topic, this post wasn't planned.
Just remembered it.