I noticed nvram replacements for the TDS784D on ebay

[radioguy123]

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

[james_s]

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.

[radioguy123]

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.

[james_s]

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.

[snoopy]

Is there anything important stored in these RAM's that would create issues swapping out the originals ?

[james_s]

No, just the settings, stored waveforms, error log, stuff like that. The cal constants are all in EEPROM on the acquisition board.

[Jwalling]

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.

[snoopy]

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

[radioguy123]

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. 

[james_s]

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.

[radioguy123]

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.

[james_s]

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.

[snoopy]

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 ?

[radioguy123]

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. 

[james_s]

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.

[oPossum]

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

[snoopy]

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

[Black Phoenix]

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.

[ArcticGeek]

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.

[radioguy123]

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 ?

[ArcticGeek]

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.

[radioguy123]

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.

[james_s]

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.

[Alfons]

I do not understand what's going on here. If the things he sells work, where is the problem?

[radioguy123]

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.