View Full Version : Reworking / replacing a Dallas DS1286 Watchdog RTC

November 6th, 2017, 04:10 PM
The IBM 295 has at least one Dallas 1286 Watchdog chip. Problem is the embedded lithium 3v cell is good for about 10 years... Board manufactured mid 93...

So, I found the DS1286 were EOL'd about 2006. Maxim bought Dallas @2001 or so, and Maxim says they stopped making the DS1286 (and later RoHS compatible models) about 2006. So any DS1286 on flea buy with datecodes post 2006 are most likely counterfit. Aside from being from China or Hong Kong, that's a give-away they are not legit. YMMV.

I'd love a drop-in replacement, but I do't see any. Peter Wendt has ground away some of the epoxy potting on a DS1287 in a successful restoration... I don't want to do this, but it is a "the war is over, and the world is burning" last resort...

The BenchMarq BQ4847 is listed as similar... but is that pin compatible...

November 6th, 2017, 04:23 PM
It looks like this is similar to what Dallas did with the DS1285/DS1287: the DS1285 is the IC that's actually in a real DS1287. In your case, the DS1284 is the bare IC in the DS1286 encapsulation. The DS1284 seems to be somewhat available (albeit from China) on eBay. I made this little adapter up to convert a DS1285 or DS12885 into a module:

http://i.imgur.com/s420rJKl.jpg (https://imgur.com/s420rJK)

It glues on top of the bare IC, and you bend the legs up and solder them to the castellated pads:

http://i.imgur.com/4dmKNITl.jpg (https://imgur.com/4dmKNIT)

The pinning is different on the DS1284/DS1286 so that exact board won't work. If you'd like, I can lay you out an adapter -- I don't have any machines to test with though. If you're handy with KiCad I can just send you my design files (the module is open source, I just haven't had time to do a writeup and get the files on GitHub).

June 20th, 2019, 11:31 AM
Funny how everything circles back to the IBM.

The Indigo2 has a DS1286 Watchdog module as well. We need to perform surgery to get it back to health. Anyone with a guide on how this might be accomplished ?

Thanks !!

June 20th, 2019, 12:23 PM
Oh, hey, I've got an Indigo2 that doesn't have a dead module yet! You folks want me to do a GW-1286-1 repair board?

June 20th, 2019, 02:00 PM

Your work is super clean. ����

June 20th, 2019, 03:02 PM
Thanks :) I'll pull up the datasheet and see if I can't knock it out tonight or tomorrow.

June 21st, 2019, 06:47 AM
Prototypes ordered from OSH Park! Ought to have boards some time next week, I paid for Super Swift Service. As long as all of the alignment is good, I'll send a panel of them off on my next China PCB order, which should be pretty soon.

July 3rd, 2019, 07:07 AM
The prototypes came in and got built up last night:

http://i.imgur.com/HCrzGQM.jpg (https://imgur.com/HCrzGQM)

My Indigo2 has developed a RAM fault and isn't coming up, just blinking the error, so I get to fix that before I can 100% test this, though there really should be no problem :p Thanks a ton SGI, for putting that piece of chassis RIGHT OVER THE NVRAM!

July 3rd, 2019, 07:42 AM

You are an amazing engineer and if you are ever in zip code 12901, look me up, I'd like shake your hand and buy you a beer.

July 3rd, 2019, 11:58 AM
Thanks! I enjoy building these little projects, and I hope that making them available helps out other hobbyists trying to hack on old gear!

We used to live in Troy, about 3 hours south of you. I'll let you know if I'm heading through to Canada :p

July 3rd, 2019, 03:57 PM
Yeah, it’s for that edge that protrudes just enough to keep the dog in the socket.

It’s so annoying.

I volunteer as tribute, can test for you.

July 3rd, 2019, 03:58 PM
The prototypes came in and got built up last night:

[img]http://i.imgur.com/HCrzGQM.jpg[/g] (https://imgur.com/HCrzGQM)!

Looks great !

July 8th, 2019, 07:48 AM
There must be something else wrong my my indigo2, I get the startup chime after changing out the RAM, but no video. So I dug out Amy's IMPACT indigo2 which of course works fine with the RTC/Watchdog. I tested the Elan graphics board from the non-IMPACT machine which works fine in the IMPACT machine. so more troubleshooting to do there!

I've set the time and date on the IMPACT indigo2 with the reworked module. I'm almost 100% certain it'll be fine, since I was able to find the full datasheet for the DS1284 (the chip inside a DS1286) and confirmed clock crystal capacitance, but I like to test things before unleashing them on other hobbyists :p

July 8th, 2019, 10:40 AM
It works! Left the machine unplugged since the last post, came up with the correct date and time! Here's a poor picture of the module installed in the IMPACT indigo2:

http://i.imgur.com/GP0ppSCh.jpg (https://imgur.com/GP0ppSC)

The battery holder clears the metal bracket, so when the battery does eventually die, you don't have to try and remove the module to change it. That works out well :)

The other indigo2 turns out to be fine as well, it just didn't like my choice of RAM. I'd stolen 64MB parity RAM out of a SPARCstation IPX, apparently that's not what it wants. It came up with the RAM from the IMPACT indigo2 installed. I did smell what seemed like a previously burned up RIFA cap stink from the PSU, so I'm going to take that apart. But, these little modules are pretty much good to go. I've got one spare prototype if someone needs one right this minute.

August 1st, 2019, 10:03 AM
Just ordered the panelized production run of these. Should be here in a week or two.

August 2nd, 2019, 08:11 AM
Nice, there has been some interest on irix.cc, let me know what you're asking, and i'll relay.


August 2nd, 2019, 09:59 AM
Should be like the other modules, $10 for the repair board (includes crystal, battery socket, and battery...crystal and battery socket installed, drop of epoxy to hold the crystal in place, back trimmed and filed so it'll sit flat). I don't have any spares to do pre-made modules but if folks want to send them to me I'll refurb and test them for $25.