Pin S1 missing on i486 CPU, would it work?

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Pin S1 missing on i486 CPU, would it work?

Postby appiah4 » 2019-6-10 @ 11:10

I got donated a bunch of CPUs. Along with a i386DX-20 with a soldered on pin that seems to be functional I got an i486 A80486DX-33 that is missing its S1 pin with nothing left in its place to solder a pin onto.

According to this spec sheet it is the A27 pin. I guess that means it's an address pin and is required to access RAM? I'm thinking this a critical pin, so the CPU wn't work without it, it is trash isn't it?
1989:A500|+512K|ACA500+|C1084S
1992:HIPPO-VL+|U5SX-33|8M|GD5428|CT2290|S2
1995:P5I430VX|P133|32M|S3T64+/MX2|V1|CT3980/32M
1998:S1573S|K6-2/400|64M|V2/SLI|CT4500/32M
2001:GA-6OXT|P3-1200|384M|GF4Ti4200|MX300
2004:K8VD|3700+|2G|X1950PRO|SB0350
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Re: Pin S1 missing on i486 CPU, would it work?

Postby Tiido » 2019-6-10 @ 11:44

Lack of A27 means that you will get 2 mirrors of 256MB every 512MB block, which possibly works just fine as long as the CPU won't go into a PCI machine where it must access stuff in the last Gbyte due to various PCI things that normally live there. That pin needs to be pulled low with a resistor on motherboard end most likely though.
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Re: Pin S1 missing on i486 CPU, would it work?

Postby appiah4 » 2019-6-10 @ 13:10

Tiido wrote:Lack of A27 means that you will get 2 mirrors of 256MB every 512MB block, which possibly works just fine as long as the CPU won't go into a PCI machine where it must access stuff in the last Gbyte due to various PCI things that normally live there. That pin needs to be pulled low with a resistor on motherboard end most likely though.


Umm.. So if I plug it into an ISA only or VLB motherboard it would work? :exclamation:
1989:A500|+512K|ACA500+|C1084S
1992:HIPPO-VL+|U5SX-33|8M|GD5428|CT2290|S2
1995:P5I430VX|P133|32M|S3T64+/MX2|V1|CT3980/32M
1998:S1573S|K6-2/400|64M|V2/SLI|CT4500/32M
2001:GA-6OXT|P3-1200|384M|GF4Ti4200|MX300
2004:K8VD|3700+|2G|X1950PRO|SB0350
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Re: Pin S1 missing on i486 CPU, would it work?

Postby weldum » 2019-6-10 @ 13:17

in theory it should work fine.
does soldering a new leg is not an option?
Ohh, the humanity :depressed:
386SX 25-C3 800-P3 900-Atom 1.6-C-D 2.13-P4 2.26-P4HT 3.0-P-DC 1.6-AFX 2.6-FX 3.3
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Re: Pin S1 missing on i486 CPU, would it work?

Postby appiah4 » 2019-6-10 @ 13:28

weldum wrote:in theory it should work fine.
does soldering a new leg is not an option?


There is absolutely no pad whatsoever left to solder a leg onto..
1989:A500|+512K|ACA500+|C1084S
1992:HIPPO-VL+|U5SX-33|8M|GD5428|CT2290|S2
1995:P5I430VX|P133|32M|S3T64+/MX2|V1|CT3980/32M
1998:S1573S|K6-2/400|64M|V2/SLI|CT4500/32M
2001:GA-6OXT|P3-1200|384M|GF4Ti4200|MX300
2004:K8VD|3700+|2G|X1950PRO|SB0350
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Re: Pin S1 missing on i486 CPU, would it work?

Postby weldum » 2019-6-10 @ 13:34

that's bad, because i've seen various processors fixed that way before, even pentium processors
Ohh, the humanity :depressed:
386SX 25-C3 800-P3 900-Atom 1.6-C-D 2.13-P4 2.26-P4HT 3.0-P-DC 1.6-AFX 2.6-FX 3.3
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Re: Pin S1 missing on i486 CPU, would it work?

Postby Tiido » 2019-6-10 @ 13:51

appiah4 wrote:Umm.. So if I plug it into an ISA only or VLB motherboard it would work? :exclamation:

You might have to solder a pulldown resistor on that pin on motherboard end but in theory it should indeed work.
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Re: Pin S1 missing on i486 CPU, would it work?

Postby rasz_pl » 2019-6-10 @ 16:55

can you make a picture? is there at least a stump in the spot?
there are conductive glues, would make really fragile connection, maybe glueing a small copper pad and sticking a pin into socket to form a friction joint when pressed could work

I havent seen ceramic 486 sliced in half, so no idea how the lead frame looks like internally, are those pins friction welded, glued?
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Re: Pin S1 missing on i486 CPU, would it work?

Postby appiah4 » 2019-6-11 @ 09:16

rasz_pl wrote:can you make a picture? is there at least a stump in the spot?
there are conductive glues, would make really fragile connection, maybe glueing a small copper pad and sticking a pin into socket to form a friction joint when pressed could work

I havent seen ceramic 486 sliced in half, so no idea how the lead frame looks like internally, are those pins friction welded, glued?


Yeah sure, see the stump attached.
Attachments
IMG_9994.JPG
1989:A500|+512K|ACA500+|C1084S
1992:HIPPO-VL+|U5SX-33|8M|GD5428|CT2290|S2
1995:P5I430VX|P133|32M|S3T64+/MX2|V1|CT3980/32M
1998:S1573S|K6-2/400|64M|V2/SLI|CT4500/32M
2001:GA-6OXT|P3-1200|384M|GF4Ti4200|MX300
2004:K8VD|3700+|2G|X1950PRO|SB0350
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Re: Pin S1 missing on i486 CPU, would it work?

Postby treeman » 2019-6-11 @ 10:50

that pad has to go somwhere, is it possible to dig in a little with a sharp knife to try find the end and add solder?
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Re: Pin S1 missing on i486 CPU, would it work?

Postby appiah4 » 2019-6-11 @ 11:45

treeman wrote:that pad has to go somwhere, is it possible to dig in a little with a sharp knife to try find the end and add solder?


This is advice I heard from elsewhere too, just scrape it until you find the copper, then solder on the pin there..

I don't have the pin either, though :lol:
1989:A500|+512K|ACA500+|C1084S
1992:HIPPO-VL+|U5SX-33|8M|GD5428|CT2290|S2
1995:P5I430VX|P133|32M|S3T64+/MX2|V1|CT3980/32M
1998:S1573S|K6-2/400|64M|V2/SLI|CT4500/32M
2001:GA-6OXT|P3-1200|384M|GF4Ti4200|MX300
2004:K8VD|3700+|2G|X1950PRO|SB0350
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Re: Pin S1 missing on i486 CPU, would it work?

Postby treeman » 2019-6-11 @ 11:54

I have a overdrive cpu that a pin fell off, I used a wire of similar thickness and length and soldered it to the pad. It will only go in a socket once and most likely fall off when you take it out, so I put it permanently in another socket/bracket like this

Image

it works just like original now, so you need to dig down for the connection, solder some new pin from a similar length and fatness material and put it in a new socket
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Re: Pin S1 missing on i486 CPU, would it work?

Postby SSTV2 » 2019-6-11 @ 13:42

Edge pads seem to be corroded and S17 pin looks like it's about to fall off. Perhaps there is a way of recreating pin connection by using conductive paint or glue, like rasz_pl stated, making it sort of "LGA" type of pad, but from the looks of it, it's probably not possible, as no metal wires are sticking out. I wonder what type of conductors were used to connect pins/pads with different layers in those ceramic CPUs.

Am5x86 133ADW guts:
1.jpg

2.jpg

3.jpg

Three layers can be seen, but no traces of metal.
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Re: Pin S1 missing on i486 CPU, would it work?

Postby treeman » 2019-6-12 @ 10:36

very very interesting, 3 layers I am guessing because 3 rows of pins so they are multilayer, looks magic no traces but the signal from the pins goes to the core. I wish I had a cpu to sacrifice because I am very curious now
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Re: Pin S1 missing on i486 CPU, would it work?

Postby Tiido » 2019-6-12 @ 12:43

There's no actual leadframe there from what I know, only sputtered gold. So there isn't anything to really solder onto. Conductive paint might be the only solution.
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