SPARCstation 20 with SCSI2SD

[Maciej W. Rozycki]

On Sun, 2 Dec 2018, Jeffrey S. Worley via cctalk wrote:

> The re-work of that Dallas nvram chip is just beautiful.  It makes me
> ashamed of myself.  (I just chopped into the epoxy with a pocket knife,
> soldered two leads, and velcroed the new batteries somewhere inside the
> machine I installed it in.)

 There is very little clearance in DECstation 5000 systems, like .1", as 
per the TURBOchannel specification, between the top of the Dallas chip and 
the bottom of any TURBOchannel option placed right above it (some have 
components underneath, including large ICs), and I think the risk of 
breaking such a non-standard wiring while shuffling option cards is not to 
be ignored either.  Also the design of the system box makes it very 
difficult to choose a suitable location for a distant battery holder that 
would not obstruct anything.

 So I decided to do that properly at the cost of it taking perhaps a 
little longer to rework a single chip.

 NB a CR1220 cell is supposed to last for ~8 years in this application if 
running on battery power all the time, which I think is good enough.  A 
CR2032 cell would last ~50 years, which I think is an overkill, given that 
the seal is expected to fail much earlier, like after 10 years.

 An encapsulated power module could instead be used such as the Renata 
175-0, where space permits, which would indeed last some 50 years, being 
airtight, but I haven't seen any reports of its use in this application (I 
have a couple of those on DEC NVRAM boards and last time I checked they 
still had the power to hold 1MiB SRAM memory contents after 25+ years).

> I salute you sir.

 :)  So far I only made 2 of these, but more are in the pipeline (waiting
for a free weekend).

  Maciej