Author Topic: Do Decoders forget?  (Read 894 times)

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djconway

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Do Decoders forget?
« on: June 16, 2014, 11:10:11 PM »
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I'm in the process of updating programming on a bunch of N scale Digitrax decoders that haven't been run since about 2004.
I found that when I try to read the MFG - it comes back as 255 - read the address  255

My notes on these locos say they were running well when put away.

So my question is do decoders die from being in the box for 10+ years?
Most of the decoders in question are DN93FX and DZ121.

reinhardtjh

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Re: Do Decoders forget?
« Reply #1 on: June 16, 2014, 11:42:10 PM »
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It's possible.  I think.  The decoders would be using some sort of non-volitile memory, probably serial eeprom.  Normally one wouldn't expect something programmed into them to erase, but I also don't know if the designers anticipated 10 year idle times with no connection to power.  The internal links might have reset over that long a time period.

I just looked up a current part, a MicroChip 11AAXXX/11LCXXX series, and it lists typical data retention time as greater than 200 years.  But I don't know what the state of the art was 10 (or 20) or so years ago when the DN93FX and DZ121 were designed/built.

Edit:
  An additional thought, it might be more likely that oxidation has caused the paths to the decoder to deteriorate to the point where the programmer is not reading a response and defaulting to a 255 value.

  Do the locomotives run properly under DCC?  That is, respond to the expected addresses?  Lights work?  Or do they do nothing at all?

2nd Edit:
  So I happen to spy my 1993 Microchip Data book on the shelf in the basement here and I look at several of the pages for various CMOS Serial EEPROMs and all that I look at say >40 years expected data retention.  So even with the DN93FX you'd expect at least another 20 years or so before they forgot.  MicroChip wasn't the only game in 1993, but they were typical so I'd expect that Nat Semi, TI and Motorola and others would have similar data life expectancies.
  Interestingly, the "normal" parallel style EEPROMS all quote a >10 year data retention.  These are all physically too big to fit in a DCC decoder so I don't expect that these parts were ever used.  I also looked at the various PIC microprocessors and most do not have any internal storage for long term - they are intended to use the serial EEPROMs if that's needed.  But the few that do have internal EEPROM don't list a data retention time.  It's possible the decoder uses this and it may be that the retention time is low, but I'd expect it to be on the same order as the serial EEPROMs.  Plus the one documented PIC that has this is too big to fit anyway.

« Last Edit: June 17, 2014, 12:15:38 AM by reinhardtjh »
John H. Reinhardt
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peteski

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Re: Do Decoders forget?
« Reply #2 on: June 17, 2014, 12:54:38 AM »
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Sometimes a voltage spike applied to the decoder (something like a surge of voltage after a short or even a static discharge from when you touch the rails) can "blow decoder's brain out".  That is what I call that.  Basically some of the internal nonvolatile memory can be erased.  But I have only seen that with the CVs you can modify - never in the ones which are hard coded. But the hard-coding is also done in a programmable read-only memory, so there is a possibility that those cells can get eased.

Can you read (and/or modify) other CVs of that decoder, or do all CVs read out as 255?
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djconway

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Re: Do Decoders forget?
« Reply #3 on: June 17, 2014, 07:27:41 PM »
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John - I wasn't able to get them to respond to DC or DCC, so your thought on oxidation may be on the mark.
CVs 1, 7, 8, 17, 18, and 29 and more all come up 255.  These decoders were installed in early 96 so they don't me anything. 
The locos were put on the shelf in the basement because they were not the best runners, so maybe its time to shop them for an overhaul.

Pete - could have been a static spike some time along the 10 year layoff, but they are handled about the same as the locos that still work. 
The locos I'm having problems with were conversion #3 4 & 5 of what is now about 200.  It would be fun to see them run again but they were $20 locos with $35 decoders.  I may find some cheep 2 function decoders and replace them.

peteski

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Re: Do Decoders forget?
« Reply #4 on: June 17, 2014, 09:27:37 PM »
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John - I wasn't able to get them to respond to DC or DCC, so your thought on oxidation may be on the mark.
CVs 1, 7, 8, 17, 18, and 29 and more all come up 255.  These decoders were installed in early 96 so they don't me anything. 
The locos were put on the shelf in the basement because they were not the best runners, so maybe its time to shop them for an overhaul.

Pete - could have been a static spike some time along the 10 year layoff, but they are handled about the same as the locos that still work. 
The locos I'm having problems with were conversion #3 4 & 5 of what is now about 200.  It would be fun to see them run again but they were $20 locos with $35 decoders.  I may find some cheep 2 function decoders and replace them.

There are couple of new Digitrax 2-function decoders selling for a street price of about $17.
« Last Edit: June 17, 2014, 09:31:09 PM by peteski »
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reinhardtjh

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Re: Do Decoders forget?
« Reply #5 on: June 18, 2014, 03:31:21 AM »
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There are couple of new Digitrax 2-function decoders selling for a street price of about $17.

Yep.  And the new ones will be a lot smaller and easier to fit.

Digitrax DZ123 are old but still available.  MBK has them for $16.
             DZ126 are the new replacement and they are $17.59
             DN136 are the new "el cheapo" decoders at MBK at $16.79 - hurry, only 320 in stock!  :scared:

But if you've done 200+ installations you are probably well aware. ;)

John H. Reinhardt
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djconway

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Re: Do Decoders forget?
« Reply #6 on: June 19, 2014, 10:28:51 AM »
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Got to see what's stashed away on the shelf.

Thanks

 :scared: Hoping the stuff on the shelf hasn't gone bad (same environment - damp basement)
« Last Edit: June 19, 2014, 02:00:25 PM by djconway »

Rich Businger

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Re: Do Decoders forget?
« Reply #7 on: June 19, 2014, 01:23:07 PM »
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You might have oxidation on the truck axle power pickups, phospher bronze strips or depending how the power is routed to the decoder a corrosion or oxidation issue inside the shell.


Rich
 

mmyers

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Re: Do Decoders forget?
« Reply #8 on: June 21, 2014, 11:51:29 AM »
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Could DN93's be read? Not sure if they had that feature. Maybe same with DZ121's.

djconway

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Re: Do Decoders forget?
« Reply #9 on: June 26, 2014, 03:33:35 PM »
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Could DN93's be read? Not sure if they had that feature. Maybe same with DZ121's.

Interesting thought, maybe I'll try programming it to what I want it to be and see if it works :?
Dig out that box again tonight.

peteski

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Re: Do Decoders forget?
« Reply #10 on: June 26, 2014, 09:36:56 PM »
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The info sheet for DN93 ( http://www.digitrax.com/static/apps/products/mobile-decoders/dn93/documents/dn93.pdf ) doesn't mention whether the CVs are write-only or can be read. You might have to contact Digitrax to confirm.  But I can confirm that DZ121 CVs can be read.
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djconway

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Re: Do Decoders forget?
« Reply #11 on: July 08, 2014, 08:32:54 AM »
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Well some more digging -
1 - DN93 can be read - they are capable of 235 addresses (why not 254? who knows) and trying to write a 4 digit address screws up just about every other setting on the poor old thing.
2 - DN123 some work as advertised some don't "new" right off my shelf - out of the bag. read as address 3 and all basic CV's read back as expected (so far so good) run it for a while as #3 no problem. Flip the switch to program, (JMRI) load the template for my E-R Sharks - write it to the decoder - no problems, run it using it's new address - no problems.  Try to tweek the speed table - problem - no responce from loco.  Drop out of JMRI and use the DT400 directly - not able to read the address.  Tyied to do a factory reset CV8=9 - no responce from loco.  Plug its address into the throttle - it works, can't change any thing but it runs.  The DZ123 was my decoder of choice for years, now years later it looks like I may have to replace them - Not fun.

After checking about 75 of my old installs I have 3 dz123 that can not be changed, and one that can not be read or changed. 5.33% failure rate is not good at the consumer level, granted some of these decoders are 10+ years old, but 5.33% is high.

I wonder how the decoders would have been if I had run them more often.  - One of the pains of collecting for, designing and trying to build a layout while raising three kids. (layout gets 3'rd 4'th rpiority if even that high at times)

In short maybe continiously rotatiing locos onto the test track may have helped. They need to be run.