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View Full Version : Leaking Dalla DS12xx "Piggyback" RTC chips



NeXT
August 14th, 2017, 08:56 PM
This was not something I expected to come across but did so by accident.
I have seen these RTC modules in various machines, notably they are sold for the Apple II as a No-Slot Clock. It's basically a 28 pin DIP socket with a Dallas RTC chip and one or two batteries potted into the cavity underneath.

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We all know from experience that getting batteries that do not leak is a crapshoot. Some brands and models never leak while others ALWAYS leak.
Anyways, I noticed on one of my modules that not only had the batteries gone flat but the leaking cells had managed to swell up the potting until a tiny split formed that allowed the battery electrolyte to leak out.

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In my instance the damage was superficial and easily cleaned up but I guess that means y'all better start keeping an eye on those RTC modules. I doubt the regular Dallas RTC modules will see the same fate as they have the battery mounted on the topside of the module where it is capped by a plastic enclosure but I have seen these modules (I have a VME SBC that has done this) soldered directly to a board and you cannot tell if they have leaked without desoldering and removing the chip.

glitch
August 15th, 2017, 05:59 AM
In sawing the CAPHAT modules off many 48T02 modules in the past few weeks, I've noticed that you can smell battery electrolyte as soon as you hit the battery pins on some of them. I'm guessing the much thicker potting on a 48T02 keeps it within the potting compound, but it apparently creeps along the battery terminals. Since the cells don't dry out as easily when potted (apparently the determining factor in shelf life in a non-discharging situation), presumably they have more electrolyte to leak when they reach end-of-life.

The good news is, most of the time lithium coin cells use a volatile organic solvent as the electrolyte, so it'll evaporate quickly if it leaks. It smells sort of like acetone, at least to me.