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Dear all,

A couple of months ago, I obtained a CSA803A. When searching the internet and this Tek forum about CSA803X and 11801X scopes, I came across several messages related to the A5 Timing Board NVRAMs’ (U500 and U511) errors E5622 and T1331. These errors occur when an NVRAM battery has gone low. These NVRAMs (U500 and U511) consist of a DS1213B smart socket, containing a backup battery, which is the socket for a regular SRAM. When the battery fails, the NVRAM can be replaced by a new one, and after starting the scope it will function again. However, with a failing battery valuable calibration constants to enhance the time interpolator linearity, that are set at the time of manufacturing, are lost (e.g. see page 6-106 of the CSA803A/C service manual). With a new NVRAM, the scope will work again, but with reduced accuracy.
To prevent loss of this calibration data for a scope which still has the original NVRAMs, this information can be read from the chip using an EPROM programmer and stored in a file. The procedure is as follows. Remove the NVRAMs from the Timing Board, IMPORTANT: this is the combination of the DS1213B smart socket with SRAM in it, i.e. do not remove the SRAM from the smart socket. Since the combination of the smart socket DS1213B and the 256kb SRAM is equivalent to a DS1230AB NVRAM (see ), choose in the programmer the DS1230AB as the chip to work on and read the content of the SRAM.
Now in case an NVRAM fails in the future, the old NVRAM can be replaced with a DS1230AB and programmed with the saved content.
I expect this to work also on the CSA803/11801A scopes.

Kind regards,
Gerard Janssen

My 11801 had that problem, but I came to the conclusion that the NVRAM contents can be regenerated via one of the menu options.

I am not about to swear that's true. The manual and the FW are so bad they make the cheapest Chinese DSO look good. But I spent a good bit of time on the topic. The conclusion I came to was that the NVRAM is used to store the results from the "Enhanced Calibration" menu operations if the scope is powered down.

At any rate, I *love* my 11801 even if it is the worst FW I've ever seen. I've got four SD-26 heads for it. And a 2nd unit in CA at my sister's for spares and awaiting shipping when she has time.

I'd be very interested in any information about any information stored in the NVRAM at the time of manufacture and how it is generated and stored.

Have Fun!
Reg

On Sun, Aug 11, 2019 at 11:49 AM, gjm45janssen wrote:

The procedure is as follows. Remove the NVRAMs from the Timing Board,

If you have to desolder the NVRAM, make sure that the board carrying it isn't grounded while desoldering, as would be the case if the 'scope is switched off but still plugged in: The earthing of your soldering iron might provide a logic low level to a write (enable) pin, possibly destroying the contents of the chip. In general, beware of transients. Depending on the chip (I haven't looked up the specs), it might be wise to temporarily connect the Vcc pin to the potential that the tip of your soldering iron is at (usually safety earth) so only a logic high level could reach the chip via your soldering iron. Most chips need a logic low level to enable writing.

Raymond

Hi Raymond,

I was curious, do you have any direct experience with
Dallas NVRAM's losing data from desoldering grounded
boards?

The reason I ask is that the Dallas 1225AD NVRAM contains
a special control chip that is continuously powered by an
internal lithium cell.

The builtin control chip's power is isolated from the Vcc
pin, so grounding out that pin will not prevent it from
protecting the internal CMOS RAM's data.

The builtin control chip disables all external control
signals (OE, WE, CE) when the Vcc supply is outside of
the manufacturer specified range of 4.5 to 5.5V (DS1225AD).

The builtin control chip further requires that external
control signals be greater than 2.2V and less than 0.8V to
be recognized.

And, the control chip requires that Vcc be valid for a
minimum of 125ms before it will end its write protection
lock, once again allowing the CMOS RAM's contents to be
altered. Protection further requires that Vcc come up from
invalid to valid faster than 300us; Vcc just meandering its
way into the valid range won't release the lock.

Manufacturer's specs are just a document, and are sometimes
wrong, which is why I am curious if you have any direct
experience with Dallas's NVRAM specifications being wrong.

Good electronics practice requires that both the circuit
board, and the soldering/desoldering equipment be grounded
in normal use. Most of us are a little casual about grounding
the circuit boards we work on, but are rock solid on grounding
our soldering/desoldering equipment, as that comes at no extra
effort when using UL soldering/desoldering stations.

If you do have any direct experience with Dallas being wrong,
I am going to have to rethink what I was taught some nearly
40 years ago by a NASA contractor that I did assembly work for.

-Chuck Harris

Raymond Domp Frank wrote:

At 2019-08-12 09:35 AM, Chuck Harris wrote:

The builtin control chip's power is isolated from the Vcc
pin, so grounding out that pin will not prevent it from
protecting the internal CMOS RAM's data.

Thank you for the refresher about the Dallas NVRAM control chip. I believe you are correct, but it's been a lot of years since I designed one into a circuit.

I think you misunderstood Raymond's intent, however. He was suggesting that you get the board's Vcc at the same level as the soldering iron's ground, not that you short Vcc to the board ground. In his scenario, anything you touch with the iron can't appear to be logic low (-5V) with respect to Vcc, which is what might trigger something. TTL in those days was pretty much always passive high, active low, to varying degrees. But the whole point is of course moot as long as the Dallas chip does its job.

Steve Hendrix

I'm pretty sure I understood what Raymond was saying.
Raymond always writes very clearly:

1) Scope plugged in, but turned *off*.

2) A5 board installed in scope.

3) Desoldering, and resoldering NVRAM.

4) Worrying about soldering iron tip grounding /WE, /CE,
or /OE, and activating the NVRAM to overwrite its contents.

.: Presents scheme to connect soldering iron's tip grounding
to Vcc, to prevent /WE, /CE, and /OE from being driven low
when desoldering/soldering them...

(Note: Since any reasonable soldering/desoldering station
has its tip hard wired to earth ground, bringing its tip's
ground to VCC is the same as grounding VCC)

What I am saying is, if the Dallas NVRAM's controller cannot
handle the grounding of /WE, /CE, or /OE, without writing to
the contents of the NVRAM, it cannot handle being powered off.
That would be a major fail for Dallas. A fail that I have never
witnessed. I was one of Dallas's early adopters, having used
some of their preproduction NVRAMs to fix my own EEPROM design
fail.

I believe the problem is that Raymond thinks the NVRAM is passing
the /WE, /CE, and /OE signals straight through to the internal
CMOS RAM, and the lithium cell is simply keeping VCC up to save
the RAM contents. I believe his thinking is that grounding out
the control signals may activate the CMOS RAM to write over some
random cell's contents.

The problem with that belief is the Dallas NVRAM's whole purpose
in being is to prevent that scenario.

One of the capabilities of the NVRAM that Dallas featured was
the designer's ability to preprogram the NVRAM, and then wave
solder the programmed part into the circuit board. Something
that I caused done thousands of times.

I first came to use Dallas NVRAM's as a young engineer, when I
believed that EEPROMS, such as the X2816 worked in the way their
data sheets implied. The early data sheets didn't emphasize that
/WE, /CE, and /OE remained functional until VCC was down to, I
think, 1.5V... This created a situation where the address, data,
and control lines for the bus all were in a race to the bottom
as the power supplies came crashing down during power off. If /WE
hit active LOW before VCC hit 1.5V, the EEPROM could get written to...
just what Raymond fears might happen with the NVRAM.

I feel badly about making that mistake, but I take some slight
solace in knowing that I wasn't the only one. I have seen X2816's
misused in dozens of products by dozens of different manufacturers.

Analyzing some of those products has shown creative software fixes
for the random data lost due to power down. Most seemed to settle
on writing the data in multiple places and voting on the rightness
of the data... before cleaning up the record.

Meanwhile, Dallas exploited that failure to take the market from
the X2816.

-Chuck Harris

Steve Hendrix wrote:

To the best of my knowledge NVRAM are always socketed. That was the case in the Sun workstations where I first encountered the issue and my 11801.

I would very much like to see an example of known good NVRAM contents from an 11801 as other people are coming to conclusions that do not correspond to mine.

Reg

Certainly not always.

Tektronix soldered them into every 2465B.

I am pretty sure that even Sun soldered them into the 3/60 and
first sparcstations.

One might have wished that they were socketed, but if a manufacturer
wanted reliability, EPROMs and NVRAMs were usually soldered.

-Chuck Harris

Reginald Beardsley via Groups.Io wrote:

Right, I do remember using ST Microelectronics real-time clocks back in the mid to late 1990's that had a semiconductor part that could go through wave or reflow soldering without damage.? Then there was the battery unit that snapped on afterward, since it couldn't take the heat of the soldering process.? May have been a 32.768 kHz crystal with the battery as well.? ST called it the snap-hat module.? Socketing would protect heat-sensitive components too.Jim Ford?Sent from my Verizon, Samsung Galaxy smartphone

Chuck and Steve,
It turns out I wasn't as clear as I intended and did not distinguish possible situations/combinations in my description.

First: No, Chuck, I never experienced data loss through handling Dallas NVRAMs of any type, in whatever way. It's been quite a few years since I last desoldered any of these NVRAMs while intending to preserve their contents. In more recent years, I only encounter them in scopes like 2465B's and I always recalibrate those anyway after replacement.

When I *did* want to preserve contents (many years ago), I always made sure that Vcc was and stayed (well) below Vccmin (4.5V) before and during handling the chip/module.
With my remarks re. the soldering iron tip, I tried to focus attention on the risk of transients with an isolated tip or inadvertently grounding an enable line when Vcc < Vccmin could not be guaranteed.

I realize I caused some confusion and think we all understand each other and I can put your mind at ease, Chuck, that based on my experience, you don't have to rethink what you were taught some nearly 40 years ago by your NASA contractor ;-(...

Raymond

Hi Reginald,

The service manual (CSA803C, p. 6-89) states in a note on error T1331 that it indicates an NVRAM battery failure and that it apparently does something with the “confidence words” in the NVRAM. Based on this, I expect that after a T1331 and replacement of the NVRAM, at power on the scope does not detect the correct “confidence words” and writes “zeros” for the calibration constants to let the scope function, but with reduced accuracy. On the other hand, if the scope is able to do a full Time Base calibration in the Automated Cal Mode as described in the CSA803C User Manual on p. 3-49 and further, then it would not make sense to store factory calibration constants which are overwritten after first use. I think that calibrating the time interpolator makes sure that all samples are taken at equidistant time. I don’t know the impact of losing this calibration on the accuracy, e.g. of a measured time delay.
Does anybody know what happens at factory calibration and could such a calibration be carried out in the home lab in case these constants are lost?

@ Raymond: in the CSA803X and 11801X scopes, the NVRAMs are in 28 pin dip sockets. No soldering needed.

Kind regards,
Gerard

Hi all, I just found some more information on the T1331 error and consequences. I have posted it in a new topic:
"11801C and the T1331 error: lost factory TB calibration data." Hope this is useful

Monica A