Correction, I mis-identified the board. It's actually either a Dell System 4XX/V, 4XX/DV, 4XXS/V, or 4XXS/DV
https://theretroweb.com/motherboards/s/dell-s … xx-v-and-4xx-dv
https://theretroweb.com/motherboards/s/dell-s … 4xx-dv,-4xxs-dv

Guld wrote on 2024-09-13, 17:41:

I recently received a 486 VLB motherboard that looked rather interesting. It has built in FDC, IDE, VGA (Cirrus Logic). […]
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I recently received a 486 VLB motherboard that looked rather interesting. It has built in FDC, IDE, VGA (Cirrus Logic).

Does anyone know the pin-out of the VGA header? It's a 10 pin connector. Is there a standard connector I can find or make for it? I'd be curious to try the on-board video.

From The Retro Web, the board appears to match the "Dell 486/MT" board. https://theretroweb.com/motherboards/s/dell-486-mt

Picture for reference. I'm still cleaning off some varta corrosion from a board that was on top of this one in a box but doesn't look too serious, other than tedious cleaning of some pins. If anyone has any recommendations for how to clean off the very light laying of junk off the ISA pins, I'd appreciate it. My fiberglass sanding pen sorta works. Or maybe I'll just remove the ISA connectors and replace them.

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Dell only seem to have specified the pinout from the 15 pin DSUB end (the actual Dell part number for the cable was 36869)

Thanks.

I bought some ribbon cable and connectors to try making my own. I figured I should be able to figure out what pin is what hopefully.

However I tried to boot the system and it didn't even POST at all.

Come to find out the varta corrosion that leaked onto the board did more damage than I thought. It looks like it dripped and hung around under the BIOS chip. I tried the gently remove the BIOS chip from the socket to clean it and the socket started coming loose from the motherboard.

So I've got a long battle ahead with this one to clean up those connections and solder a new socket in place and see what else might be broken. So unfortunately this one will be worked on in the background for a bit. Just working on neutralizing all the corrosion now so it at least doesn't get worse 😀.

Guld wrote on 2024-09-13, 17:50:

Correction, I mis-identified the board. It's actually either a Dell System 4XX/V, 4XX/DV, 4XXS/V, or 4XXS/DV

Looks like the photo on MT entry is also of 4xx

Guld wrote on 2024-09-13, 17:50:

https://theretroweb.com/motherboards/s/dell-s … xx-v-and-4xx-dv
https://theretroweb.com/motherboards/s/dell-s … 4xx-dv,-4xxs-dv

'Corporate needs you to find the differences between this picture and this picture'

At least 3 of those ISA slots look pretty nasty. If it was up to me, I would opt for replacing the slots altogether as I would be concerned about the corrosion you can't see (on the underside, where the slots meet the board).

It's quite obvious pins 1,3,5 on VGA header are RGB signals, doesn't matter which one is which at this point, can be re-wired later to find the right mapping.
The h-sync,v-sync lines can be found by probing continuity between pins and nearby resistors R5,R8. If monitor will show "signal out of range" then swap them.
The ground can be visually traced from the back of the motherboard, and I suspect pins 2,4,6 are ground to match nearby R/G/B. Or can be just probed with multimeter, there's plenty of grounds around for reference. Actually I bet the whole row 2/4/6/8/10 is ground, and hsync/vsync are 7,9 (no way to visually detect what is what). Well, maybe not the whole row if that header has ID/DDC included...
This should be enough to kick-start the pinout probing.

A guy on YouTube made several video about this board (or a close variant). Here is one where you can see the VGA cable attached to the header:
https://www.youtube.com/watch?v=pd6jJ8FaBYI

Note he starts the video with a 386 board for some reason, then switches to your 486 board at around 5:30, and then talks about the onboard video at around 9:00. At 9:20 you can see the VGA cable connected to the onboard header.

Luckily he also made a whole video dedicated to the pinout of the cable. He doesn't identify the signals by function, but he identifies them by color (at both ends of the cable) so you should be able to recreate the same connections.
https://www.youtube.com/watch?v=afFiaq7TGvU

Thanks for the suggestions on the VGA header, that should give me a good start.

mx597 wrote on 2024-10-02, 06:00:

At least 3 of those ISA slots look pretty nasty. If it was up to me, I would opt for replacing the slots altogether as I would be concerned about the corrosion you can't see (on the underside, where the slots meet the board).

Yeah, I tried to clean them up but it's not going great. I've got some replacement ISA slots, so I might just remove the old ones and go from there. The joys of trying to remove something with that many pins....oy.. 🤪 . Desolder gun will make that easier but still a pain I'm sure.

Guld wrote on 2024-10-03, 00:26:

Thanks for the suggestions on the VGA header, that should give me a good start.

mx597 wrote on 2024-10-02, 06:00:

At least 3 of those ISA slots look pretty nasty. If it was up to me, I would opt for replacing the slots altogether as I would be concerned about the corrosion you can't see (on the underside, where the slots meet the board).

Yeah, I tried to clean them up but it's not going great. I've got some replacement ISA slots, so I might just remove the old ones and go from there. The joys of trying to remove something with that many pins....oy.. 🤪 . Desolder gun will make that easier but still a pain I'm sure.

I would be a little scared of trying to desolder a slot connector without either a desoldering gun or a hot air station... doing each pin individually with a soldering iron and either a manual sucker or solder wick is going to dramatically increase the chances of damaging the board. I couldn't tell if you do have a desoldering gun or if you wished you had one, but if you do have one, remember that adding fresh solder to stubborn pins makes it a lot easier to desolder them.

Sacrifice the thing you are replacing, chop it up with sidecutters, slice it into small chunks with a dremel, that sort of thing.

mx597 wrote on 2024-10-03, 23:30:

[I couldn't tell if you do have a desoldering gun or if you wished you had one, but if you do have one, remember that adding fresh solder to stubborn pins makes it a lot easier to desolder them.

Ah, sorry, yeah, I've got a desoldering gun. That thing is worth it's weight in gold! And yes, I've got flux I can add to stubborn pins as well as add solder as needed. And can take my time with it. It's a side project so I'm in no rush. I'll see if I can even get it to POST before I spend too much time on it trying to remove ISA sockets.

Guld wrote on 2024-10-04, 01:10:

Ah, sorry, yeah, I've got a desoldering gun. That thing is worth it's weight in gold!

Indeed it is! When I first saw one, I still remember thinking "that thing looks pretty cool, but it's kinda expensive". What a fool I was... it is such a game changer.

Guld wrote on 2024-10-04, 01:10:

I'll see if I can even get it to POST before I spend too much time on it trying to remove ISA sockets.

Good plan. Even with a desoldering gun, removing slots does take a non-trivial amount of time, so making sure it can at least POST is a good idea.