[volt-nuts] HP 3458A CMOS RAM

Mike S mikes at flatsurface.com
Fri Aug 27 12:06:58 UTC 2010

At 12:45 AM 8/27/2010, Victor Silva wrote...
>1999~2000. My unit contained two Dallas DS1230Y and one DS1220Y 
>...On the subject of using FRAMs. In my previous assessment, FRAMs 
>cannot be used ... calculated that the FRAM would last 1~3 months of 
>powered up
>service, whereupon it would become a volatile device.

I've fixed a couple of IOtech EX488 boxes, which use a DS1216E with 
similar old-age problems. The DS1216E is a DIP socket which makes a 
8x32K CMOS RAM chip nonvolatile, and also adds a real time clock. 
Internally, it's a couple of small lithium cells and a Dallas DS1315 
chip. I suspect the DS1220Y and DS1230Y use a similar design, probably 
using a DS1312.

I was able to use a Dremel tool to remove enough of the encapsulation 
so I could pull the batteries on the failed DS1216s. I then ran some 
small wire to external CR2032 battery holders (much greater capacity 
than the smaller cells which fit in the DS1216s). Finally, I replace 
the 1990s era CMOS ram chip with a modern one (.1 uA typ vs. 100 uA max 
standby draw). Because the 1315 works by selecting the best of the two 
batteries, battery replacement is easy - do one, then the other. Self 
discharge and parasitic discharge are the main factors to life now, so 
these should be good for 20 years without new batteries.

One could pretty easily do something similar with the 1220/30 devices. 
If not direct surgery, then get a couple of DS1312s and hack up some 
sockets to provide non-volatile support using replaceable batteries.

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