Author Topic: I noticed nvram replacements for the TDS784D on ebay  (Read 2614 times)

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Offline radioguy123

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I noticed nvram replacements for the TDS784D on ebay
« on: November 19, 2019, 12:35:25 am »
Just wondering if anyone has bought the nvram replacements for TDS series scopes from this ebay seller.
It would be great if these were the real deal. If so I wonder how he does it.
Here is the ebay link.

https://www.ebay.com/itm/Tektronix-TDS784D-700x-600x-exact-functional-replacement-for-DS1486-and-DS1250Y/302913384290?hash=item46870b6f62:g:uuwAAOSw9V5bFXZt
 

Offline james_s

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #1 on: November 19, 2019, 01:16:36 am »
There's nothing particularly challenging about building a NVRAM. The RTC parts are considerably trickier but some can be replaced by newer Dallas parts as I did for the DS1742W.

$100 though?? Maybe a $30 kit would pique my interest, otherwise I'll just hack new battery into mine when I reach that point.
 

Offline radioguy123

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #2 on: November 19, 2019, 02:50:00 am »
Yeah that's what I thought. $100 does seem a bit steep.
But since their not making these parts anymore what are we going to do ?
I haven't seen anyone hacking into a DS1486. I have heard they have 2 batteries.
 

Offline james_s

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #3 on: November 19, 2019, 03:40:55 am »
Looking again I see it says you get a set of two chips for that price so I suppose that's not too bad considering what new Dallas parts cost. Looks like it's the same PCB for both only one has what I suspect is a 8 pin RTC chip on it. The NVRAM is trivial, the RTC less so. I wonder if he's using an ARM microcontroller to go between the parallel bus and serial RTC. The pictures look like they are deliberately concealing the bottom with whatever ICs are used.
 

Offline snoopy

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #4 on: November 19, 2019, 04:28:53 am »
Is there anything important stored in these RAM's that would create issues swapping out the originals ?
 

Offline james_s

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #5 on: November 19, 2019, 05:30:19 am »
No, just the settings, stored waveforms, error log, stuff like that. The cal constants are all in EEPROM on the acquisition board.
 

Offline Jwalling

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #6 on: November 19, 2019, 10:13:11 am »
No, just the settings, stored waveforms, error log, stuff like that. The cal constants are all in EEPROM on the acquisition board.

Options and SPC constants are stored in the DS1486, but options are easily recovered.
Jay

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Offline snoopy

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #7 on: November 19, 2019, 12:07:35 pm »
No, just the settings, stored waveforms, error log, stuff like that. The cal constants are all in EEPROM on the acquisition board.

Options and SPC constants are stored in the DS1486, but options are easily recovered.

Then if it only costs 100 bucks it's still a great deal considering the capability of these scopes ;)
 

Offline radioguy123

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #8 on: November 19, 2019, 01:41:49 pm »
Yes I noticed that both of the boards in his picture are labeled 1486. Just the populated parts are different, at least on top.
He does look like he is concealing what ever is on the bottom of the board.
That's why I was wondering if anyone had taken him up on the deal.
So we could reverse engineer.  8)
 

Offline james_s

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #9 on: November 19, 2019, 06:32:52 pm »
On one hand it's clear he's just a hobbyist trying to make a few bucks on his project and he's not gonna get rich selling these things so I don't really want to screw him. On the other hand I'd really like to know how they work because I've dealt with these Dallas parts before and am always curious about this sort of thing and given a choice I'd rather roll my own than buy something anyway.
 

Offline radioguy123

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #10 on: November 19, 2019, 07:33:57 pm »
You can tell there is a chip on the bottom. But you can't see what it is. Probably the ram.
Then there is probably something else under the battery.
It would be nice to be able to roll our own.
 

Offline james_s

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #11 on: November 19, 2019, 08:17:42 pm »
Assuming that 8 pin IC is a RTC, it's gonna need a microcontroller to talk to that and talk to the parallel bus. Actually this might not be all that hard to sort out just knowing what we know. Microcontroller to connect to the 8 data lines and chip select, enough of the address lines to decode when the RTC registers are being read. Some of the modern microcontrollers should be fast enough to directly talk to the parallel bus. Then you need a SRAM and power control IC.
 

Offline snoopy

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #12 on: November 20, 2019, 12:02:57 am »
You can tell there is a chip on the bottom. But you can't see what it is. Probably the ram.
Then there is probably something else under the battery.
It would be nice to be able to roll our own.

Is it really worth the time when you can buy it ready to go for 100 bucks ?
 

Offline radioguy123

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #13 on: November 20, 2019, 12:39:41 am »
Yeah you're probably right snoopy. He will even load them with the software of your choice.
Just handing over the money won't help you learn anything though.  ::)
« Last Edit: November 20, 2019, 01:03:37 am by radioguy123 »
 

Offline james_s

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #14 on: November 20, 2019, 12:59:20 am »
It's not really worth the time, but I'd still prefer to roll my own, I just like doing things that way. Also I'm curious how it's done.
 

Online oPossum

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #15 on: November 20, 2019, 02:05:34 am »
 

Offline snoopy

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #16 on: November 20, 2019, 04:03:11 am »
Yeah you're probably right snoopy. He will even load them with the software of your choice.
Just handing over the money won't help you learn anything though.  ::)

But you have probably got better things to do with the scope than trying to fix it. Don't get me wrong I have had to fix some of mine but if there is an easier path to go down it's probably worth the time you save ;)
 

Offline Black Phoenix

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #17 on: November 20, 2019, 05:37:14 am »
The only thing I would change on his design was to instead of soldering the batteries directly to the PCB and using the batteries with spot-welded legs were to change to CR2032 holders and batteries.

Probably similar to this... http://www.glitchwrks.com/2018/03/17/gw-1244-1


Exactly like that.
 

Offline ArcticGeek

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #18 on: November 20, 2019, 03:22:38 pm »
I actually purchase one of these just because I was very curious how he designed this.  I only purchased the DS1486 replacement, and he was willing to sell that to me for $70.   This is still very expensive, but I had to know what he did.

The central part of the design consists of a DS1384 RTC controller; this part is identical to the DS1486 without an SRAM.  The DS1384 sits underneath the battery, and an SRAM is on the bottom side of the board.  Once you add the SRAM to the DS1384, you have something that is identical to a DS1486.  I suspect this is exactly what is inside the encapsulated DS1486 - a DS1384, an SRAM, and a couple of coincell batteries.  The DS1384 actually has inputs for TWO backup batteries if desired. 

I must admit it's a fairly clever design, although the layout seems less than optimal.  The bad part of the design is that the DS1384 is obsolete just like the DS1486, so if you buy any of those parts you will have to buy off of Alibaba, Ebay, or a broker somewhere so the quality is questionable.  However, the DS1384 does not have an internal battery like a DS1486 does so it is arguably less risky to buy these parts.  But I worry that the mileage on these parts may vary wildly.

After paying $70 for one of these from Ebay I have been busy trying to design my own DS1486 replacement.  I actually have a design complete, both the schematic and PCB layout are done.  What I did was use an available DS1746 as a sub for the DS1486, but I re-map the regs from lower memory to upper memory that the DS1486 requires.  I do this by inverting address bits A4-A16 and then using a GAL16V8 to remap A0-A3. 

I think this will work, but there are some differences between the 2 register banks if you look at the datasheets.  For example, the enable oscillator (EOSC) bit is in a different spot...but I doubt if the TDS sets/clears it.   I won't know if it works until I actually get my boards back and test it.
 

Offline radioguy123

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #19 on: November 20, 2019, 06:34:14 pm »
So articgeek this guy is actually not telling the truth about his part not being obsolete ? Or has he actually found another part that he is using now.
How long ago did you buy this part from him ?
 

Offline ArcticGeek

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #20 on: November 20, 2019, 07:11:59 pm »
I purchased this part from the seller on Ebay in the middle of September this year.   The DS1384 is definitely obsolete,  but the datasheet is still available on the Maxim website.  I don't know when the DS1384 became obsolete, but the DS1486 went obsolete somewhere around 2009, so I'm guessing it was around that time.

Even though the DS1384 is obsolete, the part does not have an internal battery so there isn't a shelf life associated with it like the DS1486.
 

Offline radioguy123

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #21 on: November 20, 2019, 07:38:44 pm »
Yeah I see a seller on ebay with some of those ds1384's. He's wanting like $17 for those.
Something tells me there is not a very large supply of those.
Still he's being a little bit disingenuous telling us that their not obsolete.
 

Offline james_s

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #22 on: November 20, 2019, 10:10:40 pm »
I don't understand what you mean, his devices that he's selling are not obsolete, i.e. they're still available newly built from him. He's not selling the bare Dallas RTC chips and claiming those are still manufactured and he's not selling obsolete devices with built in non-replaceable batteries. His product looks 100% legit to me. True he won't be able to build them forever but that's the case for anything.
 

Offline Alfons

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #23 on: November 20, 2019, 10:37:00 pm »
I do not understand what's going on here. If the things he sells work, where is the problem?
 

Offline radioguy123

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #24 on: November 20, 2019, 11:11:21 pm »
Well I was told above by articgeek that the DS1384 that he uses to make these knockoff's are obsolete. So he will run out and not be able to make more.
Also he says that the devices that he uses to make these from are not obsolete in his ebay ad. Unless he has found another chip other than the DS1384. that is a lie.
« Last Edit: November 20, 2019, 11:13:49 pm by radioguy123 »
 

Offline james_s

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #25 on: November 20, 2019, 11:44:47 pm »
You're either being extremely pedantic or you are confused. Explain to me what difference it makes if one of the parts he's using to make these is still manufactured or not because I don't grasp it? I also don't see where he says the parts he makes them with are currently available, obviously the potted blocks from Dallas are obsolete because they are no longer made and they have non-replaceable internal batteries so they will all become stale and die. His parts are obviously not obsolete because he's still manufacturing them. One of the ICs he uses to make them is no longer made but so what? He still has them and is still manufacturing his part, his devices that he is selling have no internal battery and are still being produced by him, so they are not obsolete. It is irrelevant whether the components they use are still produced or not provided he has sufficient stock to supply the demand.

Calling it a lie is frankly absurd. The issue here is your reading comprehension. I just went and looked and it says "This part is not obsolete with no replacement like the original." That means the part (this assembly he is selling) is currently manufactured and available, you can buy one right now and you will get a brand new assembly. This is in contrast to the DS1486 which is no longer produced and no longer sold, you cannot go and buy a brand new one anywhere, they are obsolete. None of this means that he has to use all currently produced parts to build it or that he must be able to supply these in infinite numbers for an infinite period of time, that would be ridiculous. No product can be delivered indefinitely, even if I design something now with all cutting edge parts, eventually some of those parts will go out of production. As long as I have sufficient stock I can continue to sell newly built products and supported, my products would not be obsolete.
 

Offline ArcticGeek

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #26 on: November 21, 2019, 01:34:46 am »
The other thing I would add is the seller's design is sound and works well, and his claim that is a 100% compatible replacement is true.  Although he may charge $70 for it, it's a decent design none the less.  I have no idea where he got his stock of DS1384 parts.  For all I know he worked for a company that bought a bunch of them and had some left over, but who knows.  My concern would be that if he bought these parts from Ebay or Alibaba the parts might be fake/faulty and fail over time.  Since these parts don't have an internal battery the shelf life concern is removed though so maybe that isn't a huge concern.

I have a number of the TDS6XX/7XX scopes, and the DS1486 that is inside them is a concern of mine.  I must confess I've purchased several (maybe 10?) of the DS1486 parts on Ebay from various vendors on Ebay.  Some work, most don't.  Most are probably either rejects or fake parts that are relabeled.  Even those that work are very questionable in my view.  I probably could have requested a refund from Ebay for these parts, but for a few dollars it's hardly worth my time and hassle. 

The DS1486 is fairly important in the TDS6xx/7xx scopes because it holds not only the time but also the SPC constants.  When the battery dies in the part you'll likely have to rerun SPC every time you power on the scope.  You will also likely get an error on startup.  That's a pain in the you-know-what.  A worse scenario is if the part fails such that the SRAM can't be read/written at all the scope will not boot.   A quick solution would be to simply replace the DS1486 with a DS1245 128K SRAM in the same package; that will keep the SPC constants alive but the date/time will still be set the same as the last time you set it on the scope.  That might be okay but I really kind of like have the date/time stamp on any waveforms I save or plot.  But that's just me, and others might find that okay.  So that's why I've started this project to design my own to replace the part - now all I need is the time to do it!

 
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Offline radioguy123

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #27 on: November 21, 2019, 10:40:18 pm »
Keep us informed on your progress Articgeek. Do you plan on using the DS1384 ? I hope you share your ideas.
 

Offline Labrat101

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #28 on: November 22, 2019, 05:48:58 pm »
the batteries are quite easy to replace . They can be rimaled out the battery can normally felt by a slight bulge in the top surface of the chip. or a small magnet will locate it as it is 3.3 lithium battery . with a little care, i takes about half an hour
the battery top lead cut and then pried  up to get the bottom lead . solder 2 wires to a new battery .
I have replaced 2 of these batteries on my 20 year old scope . :phew:
« Last Edit: November 22, 2019, 05:58:33 pm by Labrat101 »
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Offline Labrat101

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #29 on: November 22, 2019, 06:15:52 pm »
You can tell there is a chip on the bottom. But you can't see what it is. Probably the ram.
Then there is probably something else under the battery.
It would be nice to be able to roll our own.
The whole top half of the chip only contains the battery and the Xtal which sits the opposite  side to the battery.
The ram is about 1mm under the bottom of the battery . about center chip . on some models the top is clipped and
can be removed removed  basically the top 1/4 inch approx is just plastic shell holder.
If it's Gets Hot its Working. If its Getting cold! it's your Coffee.
 

Offline james_s

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #30 on: November 22, 2019, 06:46:04 pm »
I think he's talking about the replacement parts being sold, not the originals.

I too have replaced the battery in a number of different Dallas bricks, although the result is not particularly pretty. I do wish they had just molded a coin cell holder into the top of the package right from the factory, potting a battery is stupid, soldering a module with a potted battery to the board in an expensive instrument is asinine.
 
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Offline Rollin Hand

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #31 on: November 26, 2019, 12:26:56 am »
Can you keep me inform about your results.I like to make one of the modules.Thanks
 

Offline cuebus

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #32 on: February 01, 2020, 07:33:40 am »
Hi all,

For a few days now I've been researching and developing a board for making a functional replacement for the DS1486 and DS1250.
I've had the ebay woes like many of us here and just can't seem to find a source for any NOS 2008 or 2009 date coded modules (which is when they stopped production?), and the nearly $100 cost for a genuine new DS1250 is just ridiculous.

First, about the DS1486:
I tore apart one of my DS1486s that is genuine, and as many of you guessed it is simply a low power SRAM chip with a DS1384FP acting as the controller, a 32khz crystal, and two tabbed BR1632 lithium cells sitting on top of the two chips. The DS1384FP (44pin 10x10mm QFP) is unobtainium as well, but I was curious about a number of sellers selling something labeled DS1384G which is a 48pin 7x7mm QFP. I was sort of expecting this to be a sanded and relabeled DS1558 or something else entirely, but after looking at several pictures of the DS1386P and DS1486P Powercap modules you can actually see a 48pin QFP on them labeled DS1384G. I'm inclined to think this may have been an internal production part that Dallas made to get the smaller, thinner footprint of the 7x7 QFP, which also seems about a millimeter shorter in height. I'm consulting Maxim right now to see if I can get a pinout of this chip but so far they don't even seem to know what I'm talking about  ::)
Nevertheless, by tracing back pins on those powercap modules and with some help and educated guesswork from the DS1558 datasheet which shares the 48 pin QFP footprint, I think I've figured out the pinout of the DS1384G.
I've made a layout on KiCad that I currently have in production at OshPark and I plan to use the Batten Allen leadframes to create a DIP package out of this and test it out.

I would love to get some feedback on board layout, since this is actually my first ever layout of this type of circuitry (usually doing audio). The layout was pretty difficult with such little board space and so many traces to run.
Also if anyone else has any thoughts on the DS1384G chip and my conclusions, perhaps I can gain some more insight.

About the DS1250:
Once again, this is fairly straightforward in using a run of the mill low power SRAM chip with a DS1312 controller. Actually, the part is labeled DS13C12, which once again, I cannot find any information about so I'm once again guessing it was an internal Dallas production part made for some specific reason. However, the ordinary DS1312 should be a perfectly suitable replacement. I'm using the 8 pin SOIC DS1312-2+. The DS1312 only has inputs for 1 battery which also matches up with the DS1250 only having 1 battery.

I would love to be able to make DS1650 exact replacements too using the (speculated) DS1610 controller, but I've not found any source for that part, and coupled with the fact that Tek scopes don't use the extra functionality it's not really necessary anyway.
 

Offline YetAnotherTechie

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #33 on: February 01, 2020, 12:42:15 pm »

I would love to get some feedback on board layout, since this is actually my first ever layout of this type of circuitry (usually doing audio). The layout was pretty difficult with such little board space and so many traces to run.


At first glance, increase the annular ring of the battery holder pins, they take a lot of heat to solder and being larger would make them more forgiving. In fact, it looks to me that most of the annular rings are very thin, especially the vias. You have enough space to make them larger and easier/cheaper to manufacture.
« Last Edit: February 01, 2020, 12:47:07 pm by YetAnotherTechie »
 

Offline cuebus

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #34 on: February 26, 2020, 08:51:15 am »
Success! I have built both boards and programmed both and they are both fully functional in my TDS540C. My guesses about the pinout for the DS1384G seem to be correct. My only wonder is if it actually uses the 2nd battery pin as this part seemed designed exclusively for powercap modules which only had one battery. Luckily, battery voltage can be monitored easily by measuring directly on the replacements.

I plan to tidy up the design on the DS1486 replacement board a bit. Once I've done that, I'll upload the gerbers here if anyone's interested in getting them made. Oshpark will make 3 boards for $6 shipped.
 
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Offline Tantratron

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #35 on: February 26, 2020, 09:03:01 am »
Success! I have built both boards and programmed both and they are both fully functional in my TDS540C. My guesses about the pinout for the DS1384G seem to be correct. My only wonder is if it actually uses the 2nd battery pin as this part seemed designed exclusively for powercap modules which only had one battery. Luckily, battery voltage can be monitored easily by measuring directly on the replacements.

I plan to tidy up the design on the DS1486 replacement board a bit. Once I've done that, I'll upload the gerbers here if anyone's interested in getting them made. Oshpark will make 3 boards for $6 shipped.
I own one TDS540C so if you're OK to build extra set with both chips, i'll pay you to save me time.
I live in France, what country do you live ?
Thank you, Albert
 

Offline cuebus

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #36 on: February 26, 2020, 11:11:50 pm »
Happy to start making these to order for anyone interested - there's at least a relatively ample supply of DS1384Gs out there and the DS1312 is still in production.
Incidentally Maxim just got back to me and confirmed the DS1384G was an internal part and will not give any information about it.

Total cost to make these in small quantities breaks down like this:
DS1250:
PCB: $2.13
DS1312 controller: $8.89
SRAM: $7.23
CR1632 Battery: $1.32
Pin Headers: $1
Total: $20.57

DS1486:
PCB: $2.13
DS1384G controller: $12.95
SRAM: $2.63
Crystal: $0.51
CR1632 Batteries: $2.64
Pin Headers: $1
Total: $21.86

Once labor, solder, flux, flux cleaner and shipping charges for materials are factored in, $50 per chip is actually not a totally unreasonable ask   ::)
I'm in the US. DM me if you're interested. I'm in the middle of preparing a move so lead time might be a week or two at the moment.
 

Offline james_s

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #37 on: February 26, 2020, 11:28:08 pm »
Nice job, I'd be interested in the gerbers, this is the sort of thing I'd prefer to build myself for fun. I had started laying out a board but if you have a working layout there's not much point in me reinventing the wheel.

IIRC there's a TI battery controller in a SO-8 package which is quite a bit cheaper than the Dallas part that does the same thing.
 

Offline cuebus

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #38 on: February 27, 2020, 10:21:36 pm »
TI's part is the BQ2201 which shares more characteristics to the DS1210 than the DS1312. Around year 1998 Dallas switched to using DS1312 inside their DS1250 modules, having previously used the DS1210. I believe the switch was due to the DS1312 having even lower battery drain.
From Dallas itself in an old change notice:
"All devices with date code 9826 or earlier will be built using the DS1210. All devices with date code 9827 or later will be built using the DS13d12.
...the  DS13d12  will  give  these  modules  50  microamp  standby  currents  (versus  5mA  for DS1210-based devices ) and will provide enhanced immunity to data loss caused by out-of-spec voltage transient."

Using the DS1312 seems like the right part here. My goal has also always been to not only build functional replacements, but as-near replicas as possible including battery count and size (DS1250 always had 1 1632 battery and DS1486 always had 2 1632 batteries).
Dallas used a variety of SRAM manufacturers for their parts, but my DS1486 had a Sony low power SRAM drawing 1 microamp during data retention in it. There are a few readily available chips on Mouser from Cypress and Alliance that meet the same data retention current draw.

Only long term tests will show whether my design will actually run these for 10 years on battery as the original guaranteed. Luckily, measuring the battery voltage is possible at all times, even when the scope is running (though I'd advise against this!)
 

Offline james_s

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #39 on: February 27, 2020, 11:51:05 pm »
Well I'll certainly make a pair of these once the gerbers are available. My scope is still working fine on the original chips but I know they're on borrowed time. I could hack in new batteries but I like the bare un-potted pcbs better.
 

Offline cuebus

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Re: I noticed nvram replacements for the TDS784D on ebay
« Reply #40 on: March 08, 2020, 08:56:01 pm »
I started a new thread for this:
https://www.eevblog.com/forum/repair/dallas-ds1486-and-ds1250-replacement-designs/

All gerbers and BOM can be found there  :-+
 
The following users thanked this post: james_s, Tantratron


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