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Amigaz
March 12th, 2009, 02:16 PM
Just got a Commodore 386DX 33mhz desktop PC which has a dead CMOS battery.
When I opened the unit it has a small socketed Dallas DS1287 looking "time keeper" circuit with these marking:

ST Z99TE9123
MK48T87B-24

Anyone know where I can find a replacement?

NeXT
March 12th, 2009, 02:26 PM
You can solder in a new battery pretty easily if you want to.

http://www.rotteneggs.com/r3/show/se/321442.html

Amigaz
March 12th, 2009, 02:31 PM
You can solder in a new battery pretty easily if you want to.

http://www.rotteneggs.com/r3/show/se/321442.html

Yeah, I've seen this page but my soldering skills are next to none.
My systems with dead DS1287 chips were saved with brand new DS12887 which were socketed with the help of a friend with soldering skillz :mrgreen:

Amigaz
March 12th, 2009, 02:33 PM
hmmmm.......... http://www.bestlaptopbattery.com/viewbattery.cfm/RTC-Memory/All-vendor/MK48T87B.htm

I can swear the chip on my motherboard looks smaller than a DS1287/12887 :confused:

Chuck(G)
March 12th, 2009, 03:16 PM
Maybe a slightly lower profile, but it's a 24-pin DIP.

Datasheet here (http://www.datasheet4u.com/download.php?id=531666)

Unknown_K
March 12th, 2009, 09:31 PM
You can solder in a new battery pretty easily if you want to.

http://www.rotteneggs.com/r3/show/se/321442.html

I tried that once with a dremel and buggered it up. Sometimes you can find a NOS Dallas chip on ebay cheap enough.

nige the hippy
March 13th, 2009, 06:47 AM
Sometimes you can find a NOS Dallas chip on ebay cheap enough.
Been through that one before, if it's NOS the battery has been powering the clock since it was NNS, and so chances are you'll be replacing dead with dead.:(

Unknown_K
March 13th, 2009, 10:47 AM
Been through that one before, if it's NOS the battery has been powering the clock since it was NNS, and so chances are you'll be replacing dead with dead.:(

I think the newer modules do not power the battery untill you install them into a motherboard.

modem7
March 13th, 2009, 05:25 PM
I think the newer modules do not power the battery untill you install them into a motherboard.
Certainly some RTC modules (such as the BQ3287) are designed in that way, but battery self-discharge means that they won't last on-the-shelf forever. Various posts on this forum show that the purchase of a replacement RTC module is a hit-and-miss affair. The battery may or may not be dead, and if not dead, may not have much 'juice' left in the battery. That will be what Nige is warning of.

Amigaz
March 14th, 2009, 12:20 AM
Just realized it's not socketed but soldered directly to the mobo :(
I was tricked by the detachable top on the chip which I thoght was the chip itself

Chuck(G)
March 14th, 2009, 08:49 AM
Just realized it's not socketed but soldered directly to the mobo :(
I was tricked by the detachable top on the chip which I thoght was the chip itself

Sometimes called a "top hat". :)

Amigaz
March 14th, 2009, 11:12 AM
Sometimes called a "top hat". :)

Makes me think of ice cream....we have an ice cream called "top hat" here ;)

I'm already in the process of desoldering the the chip using a desoldering braid...it's going painfully slow because of my poor soldering skills :mad:

Druid6900
March 15th, 2009, 02:11 PM
I'm already in the process of desoldering the the chip using a desoldering braid...it's going painfully slow because of my poor soldering skills :mad:

I'd stop now.

Braid is fine for two sided boards and cleaning excessive solder on the top and bottom pads, but, for multilayer boards, you have to leave the heat applied for too long and if, by some miracle, it gets the solder out of the vias, you'll have long ago delaminated the pads and part of the trace.

If you try to pry the device out, you'll rip the vias out with them.

Your best bet, and something I would only do as a last resort, is to crush the Dallas, snip the pins, heat up the joint for 5 seconds and pull the pins out with some needlenose pliers. Let the pads cool, braid up as much of the solder as you can in 5 seconds and do the same on the bottom layer.

Let the pads cool again and then reheat them from the top and bottom. This will, hopefully, thin the solder along the length of the vias so that you can get the pins for a socket in there.

Chuck(G)
March 15th, 2009, 05:26 PM
I'd stop now..

Yeah. My tool of choice is the big Soldapullt. Cutting the old chip out is good advice. If you cut the top of the leads short enough, the Soldapullt will even suck them out with the solder sometimes.

On delicate stuff, I'll use a low-temp alloy such as Chip-Quik or Zephyrtronics "Lowmelt" alloy to co-metallize the existing solder.

Unknown_K
March 15th, 2009, 07:36 PM
For thru hole stuff this works for me:

http://www.radioshack.com/product/index.jsp?productId=2062731

Druid6900
March 15th, 2009, 07:47 PM
Personally, I never found a bulb desolderer that had the vaccum power of a Snort extractor, but, if it works for you, more power to you.