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Ideas to identify this PCB mounted memory battery and its nominal voltage?

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fastline

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Long story short, I have a robotic total station. They have a timed alarm that is programmed to come up after so many years warning to have the machine sent in for service to replace the PCB mounted battery, which maintains apparently ALL the software and settings. It is a VERY expensive deal to send one in. Probably not a big deal on a newer one where you are making money with it, but I just use this older one for basic things.

The alarm has activated and I have opened the machine to take a peek at the battery. There is a duplex of stacked boards in there. I pulled the first one back and kept all ribbon cables attached. I knew the battery was on the back board and on the back side of it. It will be rather tricky to pull the second board but I can do it, and when it is 'really" time for battery, I was going to jumper in a new battery before cutting the old one so I don't lose anything. The process has risk so I don't want to do it until it is really time.


i found the location of the battery from the front side of the second board and tested only at the solder joints. I found 8V exactly. The problem is because I have not pulled the second board, I simply cannot know what the configuration of the battery is so I can know its condition! What I am thinking is this may be a series pack or 3.6*2 nominal or full charge of maybe 4.2*2. If I am right that would be a nominal of 7.2V and a full charge of 8.4V, meaning I have YEARS left before dealing with that battery issue.

Bottom line is the batteries in these are a big financial burden for everyone that owns them, and the mfg has leveraged this to ensure a recurring income from this basic repair, instead of simply making the thing DIY serviceable. I don't like being strong armed and the cost to replace the battery is higher than the machine value so I intend to do anything I need to, to maintain memory. I am wondering if I can make some assumptions based on the current voltage or if I will just have to get the back board out and look at the battery to know what we have?
 

fastline

Member
Figured I would try to provide more info to get the ball rolling with ideas?

What I gathered in the way of scarce info so far is the 8V I tested on one side of the machine may be a rechargeable pack designed to charge when the unit is running and help hold memory when turned off, reducing the demand on the other maint bats. Once that is depleted, the maint batts carry the load.

On the opposing side, I found 2, 3V button cells. The issue I have right now is one tests at .8V, the other at 3V. I found this odd because I expected them to be in parallel. You can see by the tabs that there really was no effort made to keep them separated but they are not touching each other right now.

I am just curious, what are the chances a board would have two discrete maint circuits? It seems odd. I would think they may have installed 2 batteries so they could be swapped out one at a time without memory loss but maybe that is wishful thinking.
 

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Les Jones

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The two cells could feed the same circuit via diodes (Schottky). This would mean that if one cell failed the other would still provide power to the volatile RAM. I would suggest tracing the circuit around the cells to confirm EXACTLY how the backup system works before removing the cells. I would even be tempted to feed power to the circuit that they backup via a diode before removing the cells. If you do not want to take this cautious approach then replace the cell that is down to 0.8 volts FIRST. I suspect that the cells are tagged CR2032 cells such as this one on ebay.

Les.
 

fastline

Member
Yes sir! They are 2032's, and I would like to go back with something even bigger so we don't have to cross this bridge again for a good long time.

FYI, there is no way I would even chance replacing these cells without an extensive plan, including repowering the board before removal. I just cannot chance losing the software. I have seen some guys jumper/solder to the battery legs with a new battery, then cut the old one out but that will prove to be a problem in this circuit due to the space constraint.

I am curious, purely based on experiences, is it unlikely that there are two discrete backup circuits, and the circuit was actually designed to chew on one battery before switching to the other? Can you explain how this might work so I know what to look for in the circuit?

Also, regarding the voltage on the batts, on a 2032, what would new voltage be? I would assume it should be higher than 3V? I cannot remember if lithiums tend to hold full voltage until depleted, then drop like a rock? If I can determine the 3V batt will hold things for a while, I might side step the repair until I really have time to do this. I am a little busy with other projects right now.
 

Les Jones

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I have no knowledge of your "robotic total station" I only found out it was some kind of surveying instrument using Google and I think there are a number of versions so I stopped looking for more information. It would be possible to design a circuit that would use one cell until it was getting low and then switch over to the other one but I have never seen it done. I suspect that it willnot be possible to get hold of a schematic to see how the backup cells are connected as the manufacturer seems to be after income from replacing the batteries. While Googling I found someone selling a main battery for one version. It is lithium ion so that fits in with your theory that the 8 volts you measusred is from a fully charged 2 cell battery. I checked the voltage of a couple of new unused CR2032s and they were bothe about 3.3 volts. I dont think I can offer any more advice.

Les.
 

fastline

Member
Thank you. I was not really looking for any detailed info specific to this unit for repair, only general information about how a circuit might be designed to draw from one battery until depleted, then move to the next one. It seems that might have been the case here or there is possibly something wrong with the circuit. Perhaps they are supposed to be parallel but the low battery corroded and lost contact. Just not sure yet. Just trying to get some ideas before we dive into it.

You are correct that schematics and such will certainly not be available. I find that typical owners are shy of even opening the covers let alone attempting a repair. OEMs seem to guard everything all the way until dead.

I think we plan to look at the CMOS goodies inside and determine what the min voltage needs to be and see where it is now so we have an idea what is going on.
 
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kubeek

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Have you tried looking for a dead or deleted unit? That would be a great help in your quest.
 

KeepItSimpleStupid

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Maxim has an IC that does this. Their battery backed up clock/calendar chips also are not really connected until inserted into a circuit, thus preserving shelf life. I'll see if I can find a reference for you. This is a common problem in a Tektronix scoope. In one case, they actually access the embedded batteries effectively surgically.
 

Les Jones

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Hi KISS,
Many thanks for posting the link about the Tektronics 2465B. I will now have a look at mine to replace the suspect capacitors and finding how to read the data from the DS1225. I realy like that scope. It would be a shame if it became unrepairable.

Les.
 

KeepItSimpleStupid

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Yep, nice scope, The B version is supposedly better. I can save you some more "work".

I need to replace the clock on a TDS340. I just have to do it. I got all of the pieces, I think, plus a FRAM and Dallas chips with the same layout as the DS chip in the 340. My notes say the TDS340 - uses the Dallas DS1644–120 32 K x 8 which isn't directly supported,, but I think it can be. I also have a USB floppy emulator that should work to install.

The 4Q is an inexpensive programmer http://www.mcumall.com/comersus/store/LeftStart.asp?idCategory=27 seems inexpensive and will support the DS122Y.

From my notes: Posted in the Yahoo group tekscopes on 15-Feb-15 https://groups.yahoo.com/neo/search?query=tekscopes

[redacted] kindly offered to copy out my [not me] old DS1225Y, onto a new DS1225AD, but he also did it onto a new FerroRAM FM16W08-SG (FRAM) IC with adapter. So far, I've installed the FRAM IC, and it's working with no issues. [redacted] assures me that it's good for a couple of decades, but just in case, I have the DS1225AD as a backup. Photos in the FRAM folder.

The GQ-4x will write FRAM if set to DS1225Y.

Once you sign up, search in page for "FRAM" or See:https://groups.yahoo.com/neo/groups/TekScopes/search/files?query=fram . Problems with CE and a programmer. Here is the FRAM adapter photo once you get access https://groups.yahoo.com/neo/groups/TekScopes/search/photos?query=FRAM

You can also find calibration data there.

There is a DS1225Y here: https://www.utsource.net/search.aspx?keyWords=DS1225Y.&page=1

and mouser has DS1225 http://www.mouser.com/Search/Refine.aspx?Keyword=ds1225, non Y versions. Probably issues with date support.
 

fastline

Member
I am getting ready to tear into this today. I learned from an old serviceman that the two batteries feed discrete channels to a regulator chip and then combined for a 3V output to a RAM chip. I am hoping that cutting out one battery at a time will prevent any loss of memory but we are considering keeping the machine turned on during this process as a safety. I can only assume that the cell that is at .8V is not doing one thing in the circuit.

He mentioned that due to the voltage knee curve for lithium, it is probably close to dropping like a rock at 3V. He said new voltage is 3.2V

Question - any idea where I can get PCB button batteries with legs on them? I would like to upgrade things to the bigger button batteries but that is subject to what is available. I don't have the ability to spot weld feet on a standard battery.
 

Mosaic

Well-Known Member
You don't have to spot weld.

Get some 'rust eater/remover' liquid from the hardware section in the paint aisle areas, home depot/lowes etc.
Use a toothpick to apply a little dab and then directly tin the battery with electronic solder at normal soldering temps. It will flow like on copper. Do this on both sides, wipe down or wash the batt to remove excess acid flux and then solder lead cuttings or copper solid core wire as legs.
This will work on nichrome/ stainless steel, most ferrous based metal alloys.

For long term battery backup you need to check out Lithium Thionyl bateries.
http://www.tadiranbatteries.de/eng/products/lithium-thionyl-chloride-batteries/overview.asp

I used one on my TEK. 2465A scope to replace the backup battery. Cheaper than the OEM unit by about 50%.
 

fastline

Member
It looks like the Thionyl batteries may not have the pins in the right orientation but I will investigate more. However, I did find factory Panasonic Magnesium dioxide batteries that seem to fit the bill. Est self discharge is .5%/yr so might be able to get aout 10yrs from them. I was going to go from 250mah to the bigger 560mah batteries just to ensure that the capacity is not a factor for life.
 

Mosaic

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The Tadiran batts are not drop ins. I simply wired it in and hot glued them somewhere convenient. But I got more mAh for < 50% price.
 
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