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cvandijk
Joined: 21 Jul 2016
Posts: 3589
Location: Netherlands
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 Posted: Wed Sep 09, 2020 7:53 am Post subject: Fix missing pin |
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I've a Cyrix Cx486DX4-75GP with 4 missing pins. Unfortunately 1 missing pin is also missing it's solder pad. It's pin D23, so I don't think it will work without it.
Is it possible to fix this? |
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crazybubba64
Joined: 03 Jul 2018
Posts: 1371
Location: WI, USA
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| Posted: Wed Sep 09, 2020 8:05 am Post subject: |
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Based on the picture, it looks like you have a tiny bit of the pad left. It's a bit of a stretch, but you may be able to solder a pin desoldered from another chip. May need to fill in the chipped area with epoxy or something to keep it in place.
Assuming the traces running to the other pins are fine, it might be salvageable.
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cvandijk
Joined: 21 Jul 2016
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Location: Netherlands
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| Posted: Wed Sep 09, 2020 8:16 am Post subject: |
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It's indeed a very very small bit of the pad, so maybe it will work.
Funny thing is, when I received it it still had the pin, but when I
barely touched it it just fell off.
I received it this way (you can see the 3 other missing pins on the right): |
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crazybubba64
Joined: 03 Jul 2018
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Location: WI, USA
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| Posted: Wed Sep 09, 2020 8:52 am Post subject: |
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| cvandijk wrote: | | I received it this way |
At least with the other pins, the pads are more-or-less intact, so those should be far easier to solder on a replacement.
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debs3759
Joined: 18 Jan 2006
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| Posted: Wed Sep 09, 2020 9:02 am Post subject: |
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The first image doesn't look fixable as the wire from the die is missing and therefore not connected to the fragment of the pad.
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Marcin
Joined: 02 Jan 2005
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Location: Poland
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| Posted: Wed Sep 09, 2020 9:19 am Post subject: |
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| debs3759 wrote: | | The first image doesn't look fixable as the wire from the die is missing and therefore not connected to the fragment of the pad. |
Exactly. I do not see clearly where it could be soldered to. The fragment of the pin stand is not connected with die. I see small point or that is only dirt. Marked on photo. Rescue that chip is mission impossible seeing condition of the rest pins.
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cvandijk
Joined: 21 Jul 2016
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Location: Netherlands
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| Posted: Wed Sep 09, 2020 9:27 am Post subject: |
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That small point blinks in the light, I need to find my magnifying glass.
The other pins are almost straightened: |
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Marcin
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henriok
Joined: 30 Dec 2007
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Location: Gothenburg, Sweden
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| Posted: Thu Sep 10, 2020 6:15 am Post subject: |
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It's entirely possible that this is a pin with no function too. Is it possible to get a document on the pin out of this particular processor? If you're lucky, you won't have to fix anything.
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cvandijk
Joined: 21 Jul 2016
Posts: 3589
Location: Netherlands
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| Posted: Thu Sep 10, 2020 6:29 am Post subject: |
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| henriok wrote: | | It's entirely possible that this is a pin with no function too. Is it possible to get a document on the pin out of this particular processor? If you're lucky, you won't have to fix anything. |
It's pin with function D23: |
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frag_
Joined: 17 Nov 2008
Posts: 4015
Location: Estonia
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| Posted: Thu Sep 10, 2020 6:33 am Post subject: |
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| If you plan using DOS and no more than 8 MB you can get away without this pin by grounding socket contact. |
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cvandijk
Joined: 21 Jul 2016
Posts: 3589
Location: Netherlands
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| Posted: Thu Sep 10, 2020 6:48 am Post subject: |
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| frag_ wrote: | | If you plan using DOS and no more than 8 MB you can get away without this pin by grounding socket contact. |
That's worth a shot, need to get a socket adapter.
Also the little point Marcin pointed out looks to be a golden dot, so maybe I'm lucky. |
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cuttingedgecs
Joined: 08 Oct 2017
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Location: Australia
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| Posted: Thu Sep 10, 2020 8:30 am Post subject: |
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| frag_ wrote: | | If you plan using DOS and no more than 8 MB you can get away without this pin by grounding socket contact. |
That might be true of A23, but I imagine something at some point will want to send/receive 32 bit data to/from the CPU. The BIOS would likely have some 32 bit processing in there for communication with the chipset at the very least. |
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frag_
Joined: 17 Nov 2008
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Location: Estonia
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| Posted: Thu Sep 10, 2020 11:04 am Post subject: |
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| cuttingedgecs wrote: | | frag_ wrote: | | If you plan using DOS and no more than 8 MB you can get away without this pin by grounding socket contact. |
That might be true of A23, but I imagine something at some point will want to send/receive 32 bit data to/from the CPU. The BIOS would likely have some 32 bit processing in there for communication with the chipset at the very least. |
Well, 486 would use 32-bit bus all the time, even in real mode.
While you in DOS and don't use any addresses abowe 8 MB you should be OK.
Main problem is restart, because first fetch is form 0xFFFFFFF0 and only after the first far jump address lines A20-A32 would become zero (and stay here in pure DOS without extenders). |
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