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Battery problem w/ Dallas DS1287

Shadow Lord

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O.k. so having identified the 386SX motherboard here I set about getting it up and running. Booted up the system and got a CMOS battery low error.

Nothing special there. My plan was to replace the DS1287 w/ DS12885 PCB. Unfortunately, this motherboard is one of the few that does not like the DS12885 chip and wants a real DS1287. No problem, I will tackle it another way - through the battery header. This is where things got interesting:

I first tried my standard case of four rechargeable batteries but i still continued to get an error with low voltage. My first thought it may be a problem with the diodes (something I have seen in the past). However, checking at pin 24 and GND of the DS1287 socket I see 4.3V as expected. My next thought was that maybe the board expects a higher voltage not to throw the error. So I tried a box w/ 4 1.5V AA batteries. Again I checked voltage at the socket and I am getting about 5.5V. However,the low voltage error remains.

Anyone have any ideas on what else could be causing the low voltage issue? With the error on resolved I can not get the system to boot - the board goes into a loop: low voltage error -> press f1 to resume -> BIOS setup -> reboots -> low voltage error.

TIA!
 

Chuck(G)

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The battery header won't help with the DS1287, which has an internal lithium cell and no external backup battery connections. Your best bet is to rework the 1287 as shown here and numerous other sites. I add a coin-cell holder to the top of the DS1287 if there's room.
 

Shadow Lord

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Hi Chuck,

I am confused. I thought the battery header was there for when the battery died on any of the xxx7 series of RTCs (e.g. DS1287, DS12887, DS1397, DS1497)? Or do you have to swap the DS1287 for the Motorola chip to use the external header?
 

glitch

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On the motherboards I've seen with a Dallas module and a battery header, there was support circuitry around the Dallas module that looked like it would either support a Dallas DS1285 or Motorola MC146818. You'd see at least a footprint for a RTC crystal.
 

maxtherabbit

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On the motherboards I've seen with a Dallas module and a battery header, there was support circuitry around the Dallas module that looked like it would either support a Dallas DS1285 or Motorola MC146818. You'd see at least a footprint for a RTC crystal.

This.

If for whatever reason the board wont support a 12885, I suppose it is safe to say it also wouldn't support a 12887. Otherwise I'd insist you just get a new production 12887 from digikey.

If that's all the case, populate the RTC crystal and associated caps if necessary and get a regular old MC146818 and use the battery header.

Modifying the DS1287 with an external battery is pretty much the worst of all worlds. No encapsulation to protect from leakage, fragility, etc.
 

Chuck(G)

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I don't agree--I've modified DS1287s and all that's needed is access to the buried pins. Encapsulation is still intact; if you're fussy, a couple of drops of epoxy over the exposed pins will ensure the encapsulation remains totally intact. The old buried cell is fully contained.

I see no reason why the result wouldn't last as a long as the discrete component situation.
 

glitch

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If for whatever reason the board wont support a 12885, I suppose it is safe to say it also wouldn't support a 12887. Otherwise I'd insist you just get a new production 12887 from digikey.

Yeah, if it doesn't work with a 12885, a 12887 definitely won't do it -- there's a 12885 inside every 12887.

Modifying the DS1287 with an external battery is pretty much the worst of all worlds. No encapsulation to protect from leakage, fragility, etc.

I don't agree either, see below.

I don't agree--I've modified DS1287s and all that's needed is access to the buried pins. Encapsulation is still intact; if you're fussy, a couple of drops of epoxy over the exposed pins will ensure the encapsulation remains totally intact. The old buried cell is fully contained.

I see no reason why the result wouldn't last as a long as the discrete component situation.

Yeah, I think you're much less likely to have a leak from a CR2032 or CR1225 coin cell than an external battery pack. Even using something like a hermetically sealed 1/2AA lithium cell, I'd bet the coin cells are far less likely to leak and do any meaningful damage.

There is of course our repair boards, or you can just patch a battery in yourself, as Chuck(G) suggested. The repair board fixes the fragility problem:

s420rJK.jpg
 

maxtherabbit

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I can get on board with a purpose built PCB like the one shown, although I sure hope there is more mechanical support than just those two folded over pins.
 

Malc

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I've never seen a leaking CR2032 coin cell, About 3 year ago i did the battery mod to the 12887 in my Amstrad 486, Works a treat, I have some NOS OEM Motherboards that have been in my shed for at least 10 years, A few days ago i dug them out and was surprised to see on the 1 board i am using the CR2032 still held a reasonable charge.
 

Chuck(G)

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You'd have to ask Glitch about that, but a blob of epoxy on top of the DIP should fix that concern. Except--and please correct me if I'm wrong--the GW board is designed around the DS12885, so the incompatibility problem would persist, unless one can locate a DS1285, which, in DIP form, seem to be pretty scarce.
 

Shadow Lord

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Hi Everyone,

I enjoy a lively discussion as much as the next guy but I think somethings are being lost here.

1. As stated in the OP I have already tried a 12885S in there on a purpose built PCB and the board refused to work with it. Yes, the module/pcb is good. I have tested it in other motherboards and they work fine. So this board for whatever reason wants an actual DS1287 (or a custom built PCB w/ a DS1285S).

2. Pictures of the board are referenced in the OP. There is a crystal nearish to the DS1287 socket and it looks like one that would be used for an RTC (as opposed to driving the bus). You can see it to the left of the keyboard connector.

The real take away here seems to be that the external battery header can NOT replace the internal battery for the DS1287. I have had other motherboards that have recommended the use of the header when the onboard batter runs out (i.e. barrel batteries (many 386/486 systems) or soldered coin battery (e.g. Compaq Proliant)) but thinking back on it none of those used a Dallas DS12xx7 module. They had the RTC/CMOS built into the chip set (e.g. NEAT).
 

glitch

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I can get on board with a purpose built PCB like the one shown, although I sure hope there is more mechanical support than just those two folded over pins.

There's two pins on each side, and they're not folded over, they're in castellated holes. We epoxy the circuit board to the DS1285/DS12885 before soldering but of course the board is open source and we also sell the repair boards for folks rebuilding dead modules on their own, so I don't know if they use epoxy or not :)

Except--and please correct me if I'm wrong--the GW board is designed around the DS12885, so the incompatibility problem would persist, unless one can locate a DS1285, which, in DIP form, seem to be pretty scarce.

We have like 20 different repair boards now, including ones for the DS1287, which use a DS1285 inside. Unfortunately it's difficult to find supplies of genuine DS1285s in DIP packaging, so we don't have ready-to-go GW-1287-1 modules on hand. We do rebuild them for folks, though. Using the repair board makes rebuilding a dead DS1287 faster and easier, though the advantage there is probably not so significant if you only have one to rebuild (we've done hundreds of DS1287s).
 

Shadow Lord

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We have like 20 different repair boards now, including ones for the DS1287, which use a DS1285 inside. Unfortunately it's difficult to find supplies of genuine DS1285s in DIP packaging, so we don't have ready-to-go GW-1287-1 modules on hand.

Are you using a DS1285 DIP or are you using a DS1285S (SOIC)? I thought the DS1285 only came as as a SOIC and FPGA packaging?

These ones are all relatively easy to replace. I have one board that uses a DS1225Y along with a DS1287. From what I can tell the DS1225Y is a combination of multiple chips plus crystal and battery. I have ordered a DS1225AD and I am hoping it will work in its place just fine.
 

glitch

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Are you using a DS1285 DIP or are you using a DS1285S (SOIC)? I thought the DS1285 only came as as a SOIC and FPGA packaging?

DIP packages, a DIP package DS1285 is what's inside a DS1287. They were available for a while. I have a very small stock of NOS DS1285s in DIP for industrial/commercial customer orders.

From what I can tell the DS1225Y is a combination of multiple chips plus crystal and battery. I have ordered a DS1225AD and I am hoping it will work in its place just fine.

Yes, the DS1225Y is a battery, low power SRAM, and a Dallas controller chip on a small circuit board. We've got a replacement for it, but I don't have pictures up. Here's the GW-1220-1 which is a replacement for the DS1220Y (very similar internally):

IV5Ept1.jpg


The original DS1220Y uses a DS1218 NVRAM controller, which is no longer produced, but we determined that a DS1312 NVRAM controller is, for this application, equivalent. It also let us add a low battery warning LED:

Mare8yS.jpg


The LED is of course only powered when the system power is on :) The purpose of doing the GW-1220-1 was to replace the dead DS1220Y in an older Prema 6.5 digit multimeter (which is 6502 based!):

4ahB9qA.jpg


Those types of replacements are 100% new designs, using Batten & Allen leadframe pins so they won't destroy old sockets, and to minimize board size. Modern low power SRAMs use a lot less power than what they had for the original DS1220Ys, so battery life should be pretty decent, even when going from a Dallas module that used two batteries internally (some did, some only used one).
 

Shadow Lord

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Yes, the DS1225Y is a battery, low power SRAM, and a Dallas controller chip on a small circuit board. We've got a replacement for it, but I don't have pictures up. Here's the GW-1220-1 which is a replacement for the DS1220Y (very similar internally):

That looks nice. When are you planning on selling the completed GW-1225-1? I would be interested in getting one for sure.
 

Hugo Holden

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Yes, the DS1225Y is a battery, low power SRAM, and a Dallas controller chip on a small circuit board. We've got a replacement for it, but I don't have pictures up.

Coincidentally I have done a lot of work on the DS1225. This is because they are used to hold the calibration constants in the TEk 2465B scope.

Firstly I organised the usual method of adding an external battery, this can be done even if the original battery remains in the module. There are some variations internally in the module in the original battery position. In addition, as the battery ages, due to the additional IC in the module, deactivates the module, before the data is lost. If the battery is on its last legs, a read will corrupt the data, but if it is supported by an added external battery it won't.

After a lot of research on the topic, I moved away from the DS1225 to Ramtron FRAM, I was the first person to install these in Tek 2465B's, partly because there was a lot of advice around saying it wouldn't work. Also it turned out that the FRAM programs in the GQ-4x programmer, when it is set for the DS1225, subsequently the FM16W08 was added to the supported list of IC's. After a few years it took off like a craze and now this is what is usually done for the Tek 2465B scope.

Here is the original article I wrote back in 2013, and I have been running FRAM in my scopes since that time. There are some interesting remarks in the article about Autostore - Shadow Ram STK12C68 option I tried and a MRAM (Magnetoresistive Ram, that never came into being, even though its data sheet circulated the net) I use this type number (CY9C6264) as a "probe" if some supplier claims to have it in stock, you can then know they are not a genuine stocking supplier.

http://worldphaco.com/uploads/TEKTRONIX_2465b_OSCILLOSCOPE_CALIBRATION___REPOWERING_THE_DS1225.pdf
 
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