Dallas Nonvolatile Ram Chips - Battery Surgery

[edpalmer42]

I'm trying to repair a 13 year old piece of equipment that has a total of 10 Dallas Nonvolatile Ram chips.  Since they're 3 years past the guaranteed life, I'd like to check them.  Nine of them are soldered in so I can't just pull them and read them.  I've searched the net and found info on battery surgery for some of these chips, but not the ones I need.  What I want to do is drill a hole to get access to the battery's positive connection so that I can measure the voltage. 

Has anyone opened up either of these chips:  DS1230AB or DS1245AB?

As a test, I drilled into a DS12887 RTC/Cmos chip near pin 20 and was able to measure the voltage with no trouble.  I just need to know where to drill.

Thanks,
Ed

[digsys]

I have 1287, 3287, 1235, 1225, 1213, 1216 in stock, but not yours. bummer.
Rather than drilling, why not attach wires (> DMM) to heated pins and gently push them into the plastic. No mess no fuss.
Or are yours solid resin?

[AndyC_772]

I think you'll find that the battery voltage remains fairly constant throughout the battery's working life, so measuring it doesn't really give a good indication of how much capacity remains. I fear you may end up having to desolder the module, then read and replace it to be sure.

[edpalmer42]

I have 1287, 3287, 1235, 1225, 1213, 1216 in stock, but not yours. bummer.
Rather than drilling, why not attach wires (> DMM) to heated pins and gently push them into the plastic. No mess no fuss.
Or are yours solid resin?

The heated pin might work, but I still don't know where to stick the pin.  I don't want to start blindly poking at the thing.

Ed

[edpalmer42]

I think you'll find that the battery voltage remains fairly constant throughout the battery's working life, so measuring it doesn't really give a good indication of how much capacity remains. I fear you may end up having to desolder the module, then read and replace it to be sure.

I agree that the voltage stays constant.  I'm wondering is if one of these ram chips has failed and that's what's causing the fault.  No service info is available so I'm fumbling around in the dark.

I'm really dreading the idea of unsoldering 9 chips without damaging either the chips or the boards.  I don't know whether a dead chip will brick the unit or whether it just holds configuration and/or calibration data that can be easily replaced.

Ed

[poorchava]

The problem is, that factory calibration data is usually impossible to replace. Only option is to send the equipment to Tek factory, and for a 13 y.o. stuff the calibration service may not be available anymore. Anyway, contents of those nvram chips are priceless

[BravoV]

Anyway, contents of those nvram chips are priceless

+1 , its the data that is matter, back up 1st before finding the solution either modding with battery or full replacement.

Just fyi, the cheap MiniPro TL866 Universal Programmer officially supports the DS1230AB or DS1245AB chips.

[nctnico]

I know it is possible to get to the battery using a grinding tool. I have seen pictures on internet from people who succesfully replaced the battery. The more daring did that with the equipment powered on so they wouldn't lose the data. Others desolder NVRAMs and back them up.

In my equipment with NVRAMs I desolderd the chips made a backup and put them in sockets. I soldered the chip into an extra socket with turned pins because leads with solder on them in a socket is asking for trouble.

@poorchava: if you pay then Tektronix will calibrate it. I recently asked to calibrate my approx. 18 year old scope and they had no problem. BTW this scope also has an NVRAM but it is still working.

[mikeselectricstuff]

If the data is critical and not readily replaceable, the safest way would be to either unsolder them and read in a device programmer, or make a device that passively reads the data in-system - fairly likely the equipment will do a checksum at startup so should scan through all the addresses. May be able to use a decent logic analyser to do this.

[amyk]

If you want to know where the battery is, you could try to get an xray of it.

There are some nonvolatile SRAMs out there that don't need a battery, and could be considered for replacement.

[edpalmer42]

Thanks for your thoughts.  All good ideas, but I'll hold off for now on any drastic moves.

To summarize my situation:
- 9 soldered-in chips that are 13 years old with a 10 year data retention spec
- dead unit so no backup or diagnostics are possible (did one of the chips fail?)
- no service information so I don't know if the info is vital or nice to have

I have some other avenues to persue, but if it comes to it, I think I'll buy one of each chip and destroy it to find the point to drill to access the battery.  The battery voltage should tell me if one of the chips has failed and caused the dead system.

FYI, the DS12887 that I experimented on showed a voltage of 2V9.  Astonishing considering the fact that it includes an oscillator and has a 1994 date code!

Thanks,
Ed

[BravoV]

Fyi, my DS1225Y from Tek 2465B dated back in 1989 (24 years) still working fine ! 

After backing up the data, deliberately put it in again to see how long it will last, btw, bought it's replacement few months ago from Digikey and its dated 2012, quiet fresh imo.

[digsys]

FYI, the DS12887 that I experimented on showed a voltage of 2V9.  Astonishing considering the fact that it includes an oscillator and has a 1994 date code!

Generally, the system goes to deep sleep and is only woken up on each timer tick interrupt. You can EASILY get shelf-life, even with a MPU
running in this fashion ! Some of those purpose made cells have well over 10yrs shelf life.
In the past, when these things were expensive and rare, I sometimes quick charged them ! You can push ~50%++ life back into them in many
cases. I've also swapped them out, using a capacitor to hold the memory during changeover. Ideas to think about.

[PA0PBZ]

So, if you find that one or more of these chips have a dead battery, then what? Replacing them will not bring back the missing data, so if it is dead now because of data corruption it will stay dead and you will not even be able to tell if the chip was the problem. Can you tell a bit more about what equipment we are talking about and what else is in there, like what processor, is there program memory like flash or eprom? Are there any interfaces or programming headers? If the data is vital there must be a way for the manufacturer to reach it without desoldering the chips i'd think.

[edpalmer42]

So, if you find that one or more of these chips have a dead battery, then what? Replacing them will not bring back the missing data, so if it is dead now because of data corruption it will stay dead and you will not even be able to tell if the chip was the problem. Can you tell a bit more about what equipment we are talking about and what else is in there, like what processor, is there program memory like flash or eprom? Are there any interfaces or programming headers? If the data is vital there must be a way for the manufacturer to reach it without desoldering the chips i'd think.

Good point - I haven't mentioned what I'm working on.  It's a Wavecrest DTS-2077 Digital Time Scope.  It's an amazing piece of equipment (when it's working!).  It can measure time intervals with a resolution of 800 fs - yes, that's femtoseconds.

It consists of a front panel with it's own processor, eprom, and NVRAM - which is socketed.  I've checked that chip and it seems okay.  That makes me hopeful that the rest are okay.  The front panel appears to be working fine.  It accepts input and tries to send it to the main processor via a 19K2 bps optical link which connects to a serial input port on the main processor board.

The main processor board is a 486/DX2-66 Multibus 1 board with eprom and ram - no NVRAM.  The next board has 8 NVRAM chips, all soldered.  There are two RF boards that also look like they're on the bus.  One of them has a soldered NVRAM chip.  On bootup, the processor board hangs with a diagnostic light that signifies a Multibus timeout.  I'm currently working through the Intel manual for the processor board to see what info I can come up with.  One thought I had is to change the processor board memory address strapping to stop it from looking at the bus.  Obviously, the unit won't work, but if it starts complaining about something - anything! - I will take that as confirmation that the processor board is working and move on to the other boards.

The fact that the socketed NVRAM is still good makes me reluctant to take any drastic action at this point.  If I can't come up with any other explanation for the system hang, I want to at least check the batteries to see if they're still good.  Drilling a small hole to probe the battery seems less dangerous than unsoldering the chip so that would be my first choice.  If it turns out that one or more is dead, then it's likely that I've lost program or crucial data and I have to talk to the manufacturer.  I haven't approached them yet because they don't release service info and only do depot repair.  I suspect that their prices are going to be way out of my league but this is such an amazing piece of equipment that I might suck it up and go for it.

Ed