VOGONS


First post, by appiah4

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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?

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 1 of 14, by Tiido

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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.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
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Reply 2 of 14, by appiah4

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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? 😲

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 3 of 14, by weldum

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

DT: R7-5800X3D/R5-3600/R3-1200/P-G5400/FX-6100/i3-3225/P-8400/D-900/K6-2_550
LT: C-N2840/A64-TK57/N2600/N455/N270/C-ULV353/PM-1.7/P4-2.6/P133
TC: Esther-1000/Esther-400/Vortex86-366
Others: Drean C64c/Czerweny Spectrum 48k/Talent MSX DPC200/M512K/MP475

Reply 4 of 14, by appiah4

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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..

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 5 of 14, by weldum

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that's bad, because i've seen various processors fixed that way before, even pentium processors

DT: R7-5800X3D/R5-3600/R3-1200/P-G5400/FX-6100/i3-3225/P-8400/D-900/K6-2_550
LT: C-N2840/A64-TK57/N2600/N455/N270/C-ULV353/PM-1.7/P4-2.6/P133
TC: Esther-1000/Esther-400/Vortex86-366
Others: Drean C64c/Czerweny Spectrum 48k/Talent MSX DPC200/M512K/MP475

Reply 6 of 14, by Tiido

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appiah4 wrote:

Umm.. So if I plug it into an ISA only or VLB motherboard it would work? 😲

You might have to solder a pulldown resistor on that pin on motherboard end but in theory it should indeed work.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 7 of 14, by rasz_pl

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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?

Open Source AT&T Globalyst/NCR/FIC 486-GAC-2 proprietary Cache Module reproduction

Reply 8 of 14, by appiah4

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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.

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Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 10 of 14, by appiah4

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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 🤣

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 11 of 14, by treeman

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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

s-l400.jpg

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

Reply 12 of 14, by SSTV2

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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:

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Three layers can be seen, but no traces of metal.

Reply 13 of 14, by treeman

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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

Reply 14 of 14, by Tiido

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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.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜