Question about Dallas clock chip modification/bypass

[onesimus]

Hello all! I recently bought an FIC 4386-VC-V motherboard from ebay. Unfortunately though, it has one of the Dallas clock chips. Now, I've seen the replacements for these, whether they be the Necroware stuff or just a new Dallas chip. However, on the back of my motherboard, near to the clock chip, someone has soldered a resistor. I've looked high and low online to try to see if this is some sort of known way to bypass the chip or something like that, but all I've seen people talking about is taking the chip out and replacing it. You see, I'm not so great with electronics like this, so I know what a resistor does, but I don't know what it's doing here. Was really hoping someone here is into electronics like that and be able to provide some info.

I just have a couple of questions:
Has anyone seen anything like this before?
What could this be for and how does this work?
Has anyone messed with this particular board and know whether or not it will POST with a dead Dallas chip? (a long shot I know)

Also, some have looked at the photos and said that the resistor is not attatched to the clock chip, but if you look closely, one of the traces that the resistor is connected to does actually does go to it, but goes somewhere else as well. Check out the top row on the dallas chip, 4th pin from the left, following the trace. You'll see it goes to the resistor.

Thanks and may the light of Christ shine in each of your lives!

 

[Chuck(G)]

Looks like field mod to give a pulldown to A6 (pin 10) on the DS1287 to pin 12 (ground). It's not a workaround. Probably makes things a bit more stable.

 

[onesimus]

Looks like field mod to give a pulldown to A6 (pin 10) on the DS1287 to pin 12 (ground). It's not a workaround. Probably makes things a bit more stable.

Ah thanks for the info, that's just the kind of info I was looking for. So it seems like it's really not doing a whole lot. Makes me wonder why do it at all, honestly. Hopefully the chip is still functional, because my soldering skills are terrible.

 

[Chuck(G)]

Given the age of the 1287, it's pretty much a lead-pipe cinch that the internal battery is pinin' for the fjords.
If you're skillful enough with a dremel or foredom tool, you can add an external coin cell. See: http://www.mcamafia.de/mcapage0/dsrework.htm and lots of other similar sites. This completely avoids the problem of "Will a new DS12887 work in my system?"

I've done this on very tight boards.

 

[onesimus]

Given the age of the 1287, it's pretty much a lead-pipe cinch that the internal battery is pinin' for the fjords.
If you're skillful enough with a dremel or foredom tool, you can add an external coin cell. See: http://www.mcamafia.de/mcapage0/dsrework.htm and lots of other similar sites. This completely avoids the problem of "Will a new DS12887 work in my system?"

I've done this on very tight boards.

I actually saw this and pretty much figured that this is the route I'm going to take, that way I don't have to remove it and risk messing up the board. It's good to know that you were able to do it on tight boards, because this one will be kinda tight, but I think it's possible if I get a small dremel bit. I wish I could do it manually somehow, like with a knife or something so I could have better control. I might get the board out and test on the clock chip a bit and see what I can do.

...at least it's not a varta

EDIT: just had an idea, is it possible to run a bodge from the right pins on the bottom of the board to a CR-2032 holder? It would be ugly, but potentially a way?

 

[modem7]

EDIT: just had an idea, is it possible to run a bodge from the right pins on the bottom of the board to a CR-2032 holder? It would be ugly, but potentially a way?

One of things done in the 1287 modification/fix is to sever the connection to the internal cell.

 

[onesimus]

One of things done in the 1287 modification/fix is to sever the connection to the internal cell.

Ah, gotcha. Thanks, modem7.

Well, hopefully I can successfully carry out this mod. This would be my first 486 system and I'm pretty excited for it. I don't have my CPU yet, unfortunately.

Again, really appreciate you guys' time.

 

[onesimus]

Hey, in this situation I'm not sure if it's appropriate to make a new post or to just edit my last one, feel free to let me know, but I just discovered an error in my original post which may end up leading to some insight. In the photo, the resistor is actually not connected to the top row of the clock chip, it's actually connected to the bottom and directly connecting two pins on the clock chip. It's confusing looking because the ROM is right under the RTC, but if you look at the photo knowing that the resistor is on the bottom row it helps to see where the RTC actually is and could possibly lead to some insight into what this mod actually is. Sorry for the confusion.

 

[Chuck(G)]

Was my observation incorrect that pins 10 and 12 are not bridged by the 1K resistor?

 

[onesimus]

Was my observation incorrect that pins 10 and 12 are not bridged by the 1K resistor?

I believe you were, but i misunderstood something initially. Plus I just wanted to correct my original post in case it ended up confusing anyone.

By the way, my cpu ended up coming in today and the board does indeed post with the dead clock chip, just can't save settings. Just dealing with a problem with jumper settings ATM. I got a cyrix dx2-80 and it's seemingly running at less than half of the rated speed, I'm getting like 33mhz even though the jumpers are set to 2x multiplier. Saw a thread somewhere else where someone had pretty much the same problem with this cpu but the thread was never resolved.

Anyway I don't want to derail the thread with that. I think I may just leave the board as-is for now, since I can easily boot into dos and use windows.

Thanks again Chuck for your time and observations, I appreciate it.

 

[super-sama]

EDIT: just had an idea, is it possible to run a bodge from the right pins on the bottom of the board to a CR-2032 holder? It would be ugly, but potentially a way?

Last I recall the ones needed (Pins 16/20) are internal and are not connected outside the module. You will still need to remove the chip, add a dual-wipe socket, do the battery mod and shove it back in.
I did the same thing to a Dallas unit two weeks ago, but thankfully it was already socketed on the board. Most of the time the battery mod is going to always look ugly, but it fixes the problem and won't continue to give you any headaches.
In my case I only have white colored hotglue sticks so this is what I came up with (below), utilizing a 2032 holder from a scrap motherboard. in hindsight it's much better than the Timekeeper fixes I've done in the past, but it still turns into a mess.

Replacements and mod boards to add to the top to make it look nicer are available on the interwebs from glitchwrks on Tindie and other places alongside full-on replacements with a modern dallas chip on the underside, but I believe these replacements use a CR1620 over a 2032.

 

[Chuck(G)]

Ugly? You could start by using a little black epoxy--and being careful with the dremel. You may also want to rotate the holder 90 degrees, so it aligns better with at least one of the pins.

I've done this in-situ with soldered-in chips in very tight spaces.

 

[Kelly Gray]

Hello all! I recently bought an FIC 4386-VC-V motherboard from ebay. Unfortunately though, it has one of the Dallas clock chips. Now, I've seen the replacements for these, whether they be the Necroware stuff or just a new Dallas chip. However, on the back of my motherboard, near to the clock chip, someone has soldered a resistor. I've looked high and low online to try to see if this is some sort of known way to bypass the chip or something like that, but all I've seen people talking about is taking the chip out and replacing it. You see, I'm not so great with electronics like this, so I know what a resistor does, but I don't know what it's doing here. Was really hoping someone here is into electronics like that and be able to provide some info.

I just have a couple of questions:
Has anyone seen anything like this before?
What could this be for and how does this work?
Has anyone messed with this particular board and know whether or not it will POST with a dead Dallas chip? (a long shot I know)

Also, some have looked at the photos and said that the resistor is not attatched to the clock chip, but if you look closely, one of the traces that the resistor is connected to does actually does go to it, but goes somewhere else as well. Check out the top row on the dallas chip, 4th pin from the left, following the trace. You'll see it goes to the resistor.

Thanks and may the light of Christ shine in each of your lives!

Underneath that plastic cover you will find a DS12885 RTC chip that's probably working perfectly. In order to make the DS12887, they soldered a crystal to pins 1 and 2 and glued it to the top of the chip. They then soldered a coin cell battery to pins 12 (gnd) and 20 (vbat). That coin cell was then glued to the top of the chip. Finally, the plastic cover was glued on to cover the whole mess.
You could carefully cut off the plastic cover, cut the coin cell battery free, and solder leads to a CR2032 battery holder.
Unfortunately you can't just connect a new battery to pin 20. The old battery has to be removed. Connecting a new battery without removing the old battery would at best drain the new battery very quickly, and at worst catch fire!

 

[onesimus]

Ugly? You could start by using a little black epoxy--and being careful with the dremel. You may also want to rotate the holder 90 degrees, so it aligns better with at least one of the pins.

I've done this in-situ with soldered-in chips in very tight spaces.

Underneath that plastic cover you will find a DS12885 RTC chip that's probably working perfectly. In order to make the DS12887, they soldered a crystal to pins 1 and 2 and glued it to the top of the chip. They then soldered a coin cell battery to pins 12 (gnd) and 20 (vbat). That coin cell was then glued to the top of the chip. Finally, the plastic cover was glued on to cover the whole mess.
You could carefully cut off the plastic cover, cut the coin cell battery free, and solder leads to a CR2032 battery holder.
Unfortunately you can't just connect a new battery to pin 20. The old battery has to be removed. Connecting a new battery without removing the old battery would at best drain the new battery very quickly, and at worst catch fire!

I very nearly succeeded in doing the above pictured mod, although it was significantly uglier and in the end did not seem to work. My only conclusion was either a dead battery or my leads weren't making good contact. I ended up getting frustrated with the whole project due to the cramped workspace and it seemingly not working when I thought I'd had it repeatedly, so I sought out one of the new replacement boards on eBay and the seller said that he offered a service where he would install it for what ended up being a very small fee. Turns out it was a member of the community who created the McIDE which I bought a few months ago. So I had no qualms in sending it out to him and now am just waiting on it to come back in the mail.