Re: DS12887 pcb substitute with battery

[alan--- via cctech]

What are you talking about?

https://www.digikey.com/product-detail/en/maxim-integrated/DS12885/DS12885-ND/1196867

-Alan

On 2017-11-21 14:16, Maciej W. Rozycki via cctech wrote:

On Mon, 13 Nov 2017, systems_glitch wrote:

Good stuff! I recently designed a module to build new DS1287 and 
DS12887

modules from the bare DS1285 and DS12885 ICs:

https://imgur.com/a/cgKm5


 Nice!

 That wouldn't solve my problem though, given the apparent 
unavailability
of DS1285 chips (in any packaging, whether surplus or used), compared 
with
the ubiquity of used DS1287 and DS1287A ones, possibly because they 
were
often socketed.  Using my systems as a reference for the Linux port I 
want
to avoid any deviation from their original specification so that 
software

does not make use of it by chance.

 As to the DS12887 and DS12887A chips -- these are still manufactured 
and
readily available, as someone mentioned a while ago, although a bit 
highly
priced, so either reworking an old one or using your alternative does 
help

cutting cost, which may especially matter if you need more than just a
few.

  Maciej

Re: DS12887 pcb substitute with battery

[Maciej W. Rozycki via cctech]

On Mon, 13 Nov 2017, systems_glitch wrote:

> Good stuff! I recently designed a module to build new DS1287 and DS12887
> modules from the bare DS1285 and DS12885 ICs:
> 
> https://imgur.com/a/cgKm5

 Nice!

 That wouldn't solve my problem though, given the apparent unavailability 
of DS1285 chips (in any packaging, whether surplus or used), compared with 
the ubiquity of used DS1287 and DS1287A ones, possibly because they were 
often socketed.  Using my systems as a reference for the Linux port I want 
to avoid any deviation from their original specification so that software 
does not make use of it by chance.

 As to the DS12887 and DS12887A chips -- these are still manufactured and 
readily available, as someone mentioned a while ago, although a bit highly 
priced, so either reworking an old one or using your alternative does help 
cutting cost, which may especially matter if you need more than just a 
few.

  Maciej

Re: DS12887 pcb substitute with battery

[systems_glitch via cctech]

Good stuff! I recently designed a module to build new DS1287 and DS12887
modules from the bare DS1285 and DS12885 ICs:

https://imgur.com/a/cgKm5

Just did a small run of 100 boards with the GW-12887-1 part number (they of
course work with the DS1285, though the number would be misleading). It
uses a 1225 cell as did the original, though the life of the original was
supposedly boosted by the potting not allowing the cell to evaporate as
much electrolyte through its (presumably imperfect) seal. I've see another
replacement that uses the surface mount version of the DS12885, but that
module requires surface mount bits and solder-down IC legs, whereas my
module just gets glued on top of the IC, and the appropriate legs bent up
and soldered into the castellated holes.

The motivation for the board was, as with yours, height restrictions. I did
a similar repair board for MK48T02 and MK48T08 timekeeper NVRAMs as used on
Sun systems -- there's an SBus slot directly over the NVRAM on some Sun
machines, which prevents the "glue a battery on top" method from working.

Thanks,
Jonathan

On Sun, Nov 12, 2017 at 7:44 PM, Maciej W. Rozycki via cctech <
cctech@classiccmp.org> wrote:

> Hi Chuck,
>
>  It's taken me a little while to respond to this one, however certain
> matters do need time to develop.
>
> On Sun, 22 Jan 2017, Chuck Guzis wrote:
>
> > On 01/22/2017 01:49 PM, Maciej W. Rozycki wrote:
> >
> > > A problem with reworking is there is sometimes very little clearance
> > >  available, so any modification has to be made in a clever way or you
> > > risk a short-circuit.  For example in DECstation 5000 systems their
> > > DS1287 chip is located in the TURBOchannel option slot area with the
> > > top of the chip almost reaching the solder side of the PCB of any
> > > option plugged in there.
> >
> > Although there are several illustrations of the DS1287 rework where a
> > coin-cell holder was placed atop the chip, there's absolutely no reason
> > why that has to be so.  A couple of wire leads away to an off-board
> > battery holder, holding, say, an ER14250 half-AA.will work just fine and
> > keep the battery away from the PCB--or a couple of alkaline AA cells,
> > which should last a few years.  No reason to stick to lithium.
>
>  Yeah, putting the aesthetic of the solution aside, in the DECstation
> there's the practical issue of making sure the wires do not obstruct
> shuffling TURBOchannel option cards and also finding a place where the
> substitute battery does not disturb the airflow such as to cause a
> component somewhere to overheat -- the whole side of the enclosure is a
> grille.
>
> > You know--"use your wetware".
>
>  That always helps, as long as it's got enough input to process, in
> particular as to what resources are available.
>
>  Mine has got that now, thanks to this thread of discussion, where I
> learnt of the existence of this small coin cell holder, and also the other
> thread mentioning wire-wrap wire and its excellent properties for small
> circuit repair/modification works.  Naturally I picked up the green
> insulation color to match what DEC used to use, at least in their
> TURBOchannel equipment. :)
>
>  So here: 
> are a couple photos of the result, meeting both the clearance requirements
> and my subjective aesthetic criteria, and avoiding the issues I identified
> above.
>
>  Taking into account the rated DS1285's standby power consumption of 0.5µA
> and the 35mAh 2.5V discharge level capacity of the CR1220 cell it will
> guarantee keeping the chip powered for 8 years.  Which I think is enough
> given the ease to replace the cell now.
>
>  For comparison the 48mAh capacity of the BR1225 cell originally embedded
> in the chip allowed for 11 years of operation and the CR2032 cell people
> seem to commonly choose allows for 50 years at its 220mAh capacity (which
> I find a bit of an overkill).
>
>  Note that I have calculated approximate cell capacities based on
> discharge characteristic curves published by cell manufacturers, as the
> rated capacities published are calculated for the 2.0V discharge level
> whereas DS1285 is specified for 2.5V minimum battery voltage required for
> correct operation.
>
>  For the record, I have measured the clearance available and it's 0.1875"
> (3/16") or 4.76mm from the top of the RTC chip to the bottom of the PCB of
> a TURBOchannel option right above it.  The TURBOchannel mechanical spec
> allows for 0.075" (3/40") or 1.91mm underneath component or lead height
> (e.g. 24-plane HX+ options have memory chips there).  Which leaves 0.1125"
> (9/80") or 2.86mm of space only.
>
>  I may yet stick a piece of insulating tape on top of the RTC chip just to
> make sure no contact happens by chance, though I think it might be an
> overkill after all.  It's not like the cell is going to pop out by itself.
>
>   Maciej
>

Re: DS12887 pcb substitute with battery

[Maciej W. Rozycki via cctech]

Hi Chuck,

 It's taken me a little while to respond to this one, however certain 
matters do need time to develop.

On Sun, 22 Jan 2017, Chuck Guzis wrote:

> On 01/22/2017 01:49 PM, Maciej W. Rozycki wrote:
> 
> > A problem with reworking is there is sometimes very little clearance
> >  available, so any modification has to be made in a clever way or you
> > risk a short-circuit.  For example in DECstation 5000 systems their
> > DS1287 chip is located in the TURBOchannel option slot area with the
> > top of the chip almost reaching the solder side of the PCB of any
> > option plugged in there.
> 
> Although there are several illustrations of the DS1287 rework where a
> coin-cell holder was placed atop the chip, there's absolutely no reason
> why that has to be so.  A couple of wire leads away to an off-board
> battery holder, holding, say, an ER14250 half-AA.will work just fine and
> keep the battery away from the PCB--or a couple of alkaline AA cells,
> which should last a few years.  No reason to stick to lithium.

 Yeah, putting the aesthetic of the solution aside, in the DECstation 
there's the practical issue of making sure the wires do not obstruct 
shuffling TURBOchannel option cards and also finding a place where the 
substitute battery does not disturb the airflow such as to cause a 
component somewhere to overheat -- the whole side of the enclosure is a 
grille.

> You know--"use your wetware".

 That always helps, as long as it's got enough input to process, in 
particular as to what resources are available.

 Mine has got that now, thanks to this thread of discussion, where I 
learnt of the existence of this small coin cell holder, and also the other 
thread mentioning wire-wrap wire and its excellent properties for small 
circuit repair/modification works.  Naturally I picked up the green 
insulation color to match what DEC used to use, at least in their 
TURBOchannel equipment. :)

 So here:  
are a couple photos of the result, meeting both the clearance requirements 
and my subjective aesthetic criteria, and avoiding the issues I identified 
above.

 Taking into account the rated DS1285's standby power consumption of 0.5µA 
and the 35mAh 2.5V discharge level capacity of the CR1220 cell it will 
guarantee keeping the chip powered for 8 years.  Which I think is enough 
given the ease to replace the cell now.

 For comparison the 48mAh capacity of the BR1225 cell originally embedded 
in the chip allowed for 11 years of operation and the CR2032 cell people 
seem to commonly choose allows for 50 years at its 220mAh capacity (which 
I find a bit of an overkill).

 Note that I have calculated approximate cell capacities based on 
discharge characteristic curves published by cell manufacturers, as the 
rated capacities published are calculated for the 2.0V discharge level 
whereas DS1285 is specified for 2.5V minimum battery voltage required for 
correct operation.

 For the record, I have measured the clearance available and it's 0.1875" 
(3/16") or 4.76mm from the top of the RTC chip to the bottom of the PCB of 
a TURBOchannel option right above it.  The TURBOchannel mechanical spec 
allows for 0.075" (3/40") or 1.91mm underneath component or lead height 
(e.g. 24-plane HX+ options have memory chips there).  Which leaves 0.1125" 
(9/80") or 2.86mm of space only.

 I may yet stick a piece of insulating tape on top of the RTC chip just to 
make sure no contact happens by chance, though I think it might be an 
overkill after all.  It's not like the cell is going to pop out by itself.

  Maciej

Re: DS12887 pcb substitute with battery

[Jon Elson]

On 01/23/2017 04:57 AM, allison wrote:

On 01/22/2017 02:46 PM, Chuck Guzis wrote:

On 01/22/2017 10:57 AM, allison wrote:

I don't know about most people but this solution has been around for
decades.

I locate the battery on the failed part with a small magnet, then
grind the epoxy down to it then pick it out with a sharp pointed
tool.  Once I expose the connection point I older two wires then
epoxy a small coin-cell holder in that spot and it s done.  I've done
this more times than I care to count and its effective and the
replacement battery some over 10 years old now have not failed.  But
just in case I have a bag of NOS replacements (and pulls from
socketed boards) all with dead batteries from age.  There is no magic
to this.

It's worth noting that the original post was about fabricating a
replacement using the DS12885A RTC chip.  However, most old PCs used the
DS1285 RTC (inside of a DS1287  module).  The DS12885A is supposed to be
drop-in compatible with the DS1285, but apparently, in some cases is not.

So there's logic in reworking the old DS1287 modules, as the DS1285 chip
is long out of production--you'll most likely have to be content with
pulls or the occasional NOS lot.

--Chuck

I haven't seen that version for a while.  The later are fully versions
are epoxy filled.
Same for the MT48T part, same fix.

The problem with NOS parts is manufacture date.  Some are really old.


Well, it doesn't really matter.  If you can find one of the 
"really old" ones, the battery can be replaced and you are 
good for 5 years or so.  There must be TONS of these old 
clock/RAM chips out there, and somebody must have saved a few.


Jon

Re: DS12887 pcb substitute with battery

[allison]

On 01/22/2017 02:46 PM, Chuck Guzis wrote:
> On 01/22/2017 10:57 AM, allison wrote:
>> I don't know about most people but this solution has been around for 
>> decades.
>>
>> I locate the battery on the failed part with a small magnet, then
>> grind the epoxy down to it then pick it out with a sharp pointed
>> tool.  Once I expose the connection point I older two wires then
>> epoxy a small coin-cell holder in that spot and it s done.  I've done
>> this more times than I care to count and its effective and the
>> replacement battery some over 10 years old now have not failed.  But
>> just in case I have a bag of NOS replacements (and pulls from
>> socketed boards) all with dead batteries from age.  There is no magic
>> to this.
> It's worth noting that the original post was about fabricating a
> replacement using the DS12885A RTC chip.  However, most old PCs used the
> DS1285 RTC (inside of a DS1287  module).  The DS12885A is supposed to be
> drop-in compatible with the DS1285, but apparently, in some cases is not.
>
> So there's logic in reworking the old DS1287 modules, as the DS1285 chip
> is long out of production--you'll most likely have to be content with
> pulls or the occasional NOS lot.
>
> --Chuck

I haven't seen that version for a while.  The later are fully versions
are epoxy filled.
Same for the MT48T part, same fix.

The problem with NOS parts is manufacture date.  Some are really old.

Allison
>