Replacing an old Dallas or Benmarq Real Time Clock

Discussion about old PC hardware.

Replacing an old Dallas or Benmarq Real Time Clock

Postby retro games 100 » 2009-9-22 @ 08:07

What's the best way? Let's assume the RTC is socketed to the mobo. I've seen instructions on the net showing you how to cut in to these things, so that you can hook up a fresh coin battery to them. I don't really fancy doing that. I've also read threads on the net saying that old Dallas DS1287 chips can be substituted for newer Dallas DS12887 chips, which I think can still be purchased. That sounds promising. However, I'm not sure if an old Benchmarq RTCs can be substituted for newer Dallas RTCs.

Any thoughts please people?
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Re: Replacing an old Dallas or Benmarq Real Time Clock

Postby rumbadumba » 2009-9-22 @ 08:40

Been thinking the same lately, as my old Compaq Portable III probably has a dead ds1287. I was going to have a go at cutting into it and using a coin cell. The replacement ds chips I've seen seem pretty dear, and I couldn't tell how new they really were. The coin cell solves the problem for once and for all doesn't it?
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Re: Replacing an old Dallas or Benmarq Real Time Clock

Postby retro games 100 » 2009-9-22 @ 09:08

rumbadumba wrote:The coin cell solves the problem for once and for all doesn't it?

Yes, I believe it does. Replace the dead battery within the RTC epoxy block with a new [coin cell] one, and you remove the problem. Although I'd rather just replace the whole socketed RTC. I wonder where RTCs can be bought at affordable prices? And whether they'd be good for most, if not all 486 mobos?
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Re: Replacing an old Dallas or Benmarq Real Time Clock

Postby retro games 100 » 2009-9-23 @ 17:32

A discussion about this issue can be found here -

http://www.vintage-computer.com/vcforum ... ght=Ds1287
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Re: Replacing an old Dallas or Benmarq Real Time Clock

Postby retro games 100 » 2009-9-23 @ 18:03

I'm tempted to get one of these -

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT

It's a DS12887 RTC, from an ebay seller in Hong Kong. The cost including shipping seems quite reasonable - about £9. The quantity in stock is nearly 100, and the seller has 100% positive feedback.
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Re: Replacing an old Dallas or Benmarq Real Time Clock

Postby rumbadumba » 2009-9-24 @ 21:14

Having read some of those articles about hacking the ds1287, it seems it's not foolproof.

http://www.walshcomptech.com/ps2/dallasrework.html

The manufacturer's website incidentally makes it clear that you may not be able to use the ds1287 or it's successors to replace other chips.

http://www.maxim-ic.com/appnotes.cfm/an_pk/503

In my case, I found the Compaq didn't have a ds1287 anyway [at least not that I culd see] but a 1.5" square of plastic labelled "lithium battery". I shan't replace it unless/until I get a hard drive that the machine can recognise.
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