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IBM 5150 won't run with 8087 fitted

cwathen

Experienced Member
Joined
Feb 1, 2018
Messages
268
Location
Bristol, UK
I picked up an 8087 for my IBM 5150 since it was going cheap. Supposedly this is a NOS part but I have my doubts.

With the copro fitted the system doesn't run - not even any sync on the display. Once taken out it runs fine. I do have position 2 on SW1 set to off as per minuszerodegrees.

The original 8088 CPU was replaced with a V20 last year but I didn't expect that to make any difference.

Anything I'm missing before sending back the 8087?
 
I assume you have followed the information here?

5 MHz part or faster and changed the link/switch.

Dave
 
It's an 8087-1 which should be 10Mhz. The switch is set correctly (although makes no difference what position the switch is in - just having the chip installed stops the system from running in any way). Pics below, would welcome opinion on whether it's a fake or not. Certainly it looks real enough, it's in a real ceramic package at least.
8087 top.jpg
8087 bottom.jpg
 
My opinion is that it is fake or counterfeit; the type D ceramic packages had a copyright year on them of 1980, not 1978 (at least the ones I've seen, verified by George Phillips' guide). The lettering also isn't quite the same as the other D8087-1s I've seen.

I'd get another D8087-1 that looks different from the one you have (with a copyright year of 1980) and see if that works.
 
I thought the 8087 was announced/launched in 1980 too. The 8086 was launched in 1978.

I was looking through some of my old Intel data books. The one from 1980 doesn't even list the 8087 in the 8086 etc. section. The later edition I have does.

I also suspect that what you have is a fake - or two 8086 chips (one labelled as an 8087)!

Dave
 
The lettering also isn't quite the same as the other D8087-1s I've seen.

Yep, there's something about the above photo that "just doesn't look quite right" (such as the spacing between characters). And I'd suspect (even if NOS), the lettering on it would be more worn/faded after approx. 40 years.
 
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Asked the seller for a refund or exchange for one that works, got a very quick refund without any explanation or asking for it back. Suspect they knew it wasn't right. The picture on the listing has a 1980 copyright date too. They are selling these en masse, I think I'll look out for a one off listing that is more likely to be what is claimed.

I'm intrigued now as to what it actually is...it seems too well made to not be a real something, just not a real 8087.

I did chuck it into the CPU socket to see if it was an 8088. It's not, but I wonder if it could be an 8086. May stick it into my Amstrad 1512 to find out.
 
I've had good experiences buying old ICs from the following ebayers:

greennovation
adeleparts2010
shuaistar20150515
2ndcall
top_electronic1980
allenlu1995 - bought from this guy multiple times always solid
hkutsource
 
I'm intrigued now as to what it actually is...it seems too well made to not be a real something, just not a real 8087.
It probably is a real 8087, just with the top painted over and relabeled to make it look new and to produce a large amount of identical-looking chips. Millions of "NOS" chips were made in China this way until 2017. Many of these don't work - either because they were broken from the beginning or did break in the process.
 
I'm intrigued now as to what it actually is...it seems too well made to not be a real something, just not a real 8087.

I did chuck it into the CPU socket to see if it was an 8088. It's not, but I wonder if it could be an 8086. May stick it into my Amstrad 1512 to find out.

It would be a better idea to just toss it. You're fortunate it didn't do anything to your XT class machine. Do you really want to chance doing anything damaging to any other system???
 
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