PeterTheWomble wrote on 2022-01-21, 10:31:

Having kept an eye out for years I've just got hold of a PC that's the same as my first one, a Commodore 486sx-25. There can be […]
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Having kept an eye out for years I've just got hold of a PC that's the same as my first one, a Commodore 486sx-25. There can be fewer safer ways of having a mid-life crisis 😀.

It powers on and goes through the POST, but won't proceed any further. It won't go in to the BIOS settings, though it does seem to recognise that I asked it to (the screen goes blank when I press F1).

I was expecting this, because rather than a CR2032 or one of those wretched barrel batteries that leak poison everywhere, the battery is held within a chip - a Twinhead TH1287.

Rather than being housed in a socket for easy removal, the chip has been soldered on to the motherboard.

The only option that seems available to me is to de-solder the chip, remove some of the casing, to expose the internal battery terminals, and add a CR2032 battery holder. I've seen various youtube videos of people doing this sort of thing.

Have others here done similar to this? I don't want to get this wrong, so would love to hear about what to do or to avoid. I'm very nervous about taking a soldering iron to it.

Thanks

hello 😀

You've given yourself quite the challenge there!

is there any possibility of replacing the part with a new(er) and functional one?

I've looked, but given the (understandably) scarce documentation of an obscure chip in an obscure motherboard I think my first preference is to resuscitate the chip I have. Either way I'll need to de-solder the chip that's there at the moment. If I replace it with a socket then at least things become a bit modular. I suspect the additional height might mean it interferes with the lowest of the ISA cards (it has a vertical riser), but I wasn't planning on adding lots of ISA cards (the video, FDD, IDE, Serial and parallel interfaces are all built in to the motherboard).

That Twinhead TH1287 should just be a Dallas DS1287 compatible part. Variants of these chips are still produced today. So if you put in a socket, you could also buy a brand new chip. I've done both and just buying a new one is way easier than opening up the old ones.

Thanks, I see a DS12887+ listed as available - but without a datasheet for the TH1287 I'm concerned that there might be unexpected differences, but I might give it a try.

Just check for the datasheet of the DS1287, the original one on the board is a 1:1 clone. The only difference is the century register at 32h on the 12887, making it Y2K compliant. Only reason it would fail is if the board uses the general register at 32h on the DS1287 - which is highly unlikely.

To be sure, install a socket instead of soldering the new one directly onto the board. Good practice in any event.

Thanks, this is giving me confidence (hopefully not too much) 😀

https://ardent-tool.com/misc/Dallas_Rework.html
I used this resource to perform my heart surgery on a dead dallas clock chip I had on a board even without desoldering it.
It is really simple and can be performed with a stanley knife and a bit of care.
Maybe that helps you, and maybe the terminals on your chip are also in the same position if it is a clone.

audiocrush wrote on 2022-01-23, 15:57:

https://ardent-tool.com/misc/Dallas_Rework.html I used this resource to perform my heart surgery on a dead dallas clock chip I h […]
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https://ardent-tool.com/misc/Dallas_Rework.html
I used this resource to perform my heart surgery on a dead dallas clock chip I had on a board even without desoldering it.
It is really simple and can be performed with a stanley knife and a bit of care.
Maybe that helps you, and maybe the terminals on your chip are also in the same position if it is a clone.

Dude . .thanks for this, I was close to desoldering a dead Dallas RTC on a Socket 7 board I have but my soldering skills are a bit rusty and my eye sight isn't much better, so being able to fix it without desoldering will be great !

PeterTheWomble wrote on 2022-01-21, 10:31:

There can be fewer safer ways of having a mid-life crisis 😀.

Yah, but I still might get a turbo sports coupe held together with hope and bondo.... 🤣