Bachmann Message Board

Discussion Boards => General Discussion => Topic started by: CNE Runner on February 12, 2012, 11:36:40 AM

Title: Look before you ask
Post by: CNE Runner on February 12, 2012, 11:36:40 AM
I have decided to sell my old Bachmann GP-35 at one of our next train shows (the old girl is 'way too large for my layout). Our policy is to test all motive power before putting them on the table (or we sell them as "non-running" or "unknown" and price them appropriately). This particular GP-35 was my first DCC locomotive and always ran flawlessly.

As per our sale policy, I decided to test the locomotive on my DC-powered Monks' Island Railway. Unfortunately the unit did not move. I (again) read what little instructional material came with the locomotive - all of which indicated it contained a dual mode decoder. Now what?

Rather than ask a question that has been asked in the past, I decided to check out the EZ Command section of the Parts & Service heading on the Bachmann website (as per a suggestion by RichG). Glory this section were complete instructions on the EZ Command Two Function Decoder! A further check of past postings on the forum indicated that CV-29 should be set to '6' to restore DC operation (I honestly don't remember changing that CV value...but then again I have trouble remembering what I did the day before yesterday). Jim Banner posted to make sure the headlight was turned ON during the reprogramming so that it will operate in DC mode...'would have never thought of that.

My point is that there is a lot of help/information a couple of key strokes away. It would make sense to check out the archives (by clicking on the 'Search' button at the top of the page) before repeating a question that was asked (and answered well) before.

Many thanks for, once again, bailing out the CNE Runner guys.


Title: Re: Look before you ask
Post by: poliss on February 12, 2012, 09:33:12 PM
There's a handy 'tick box' CV29 calculator here.
Also does CV17/18.

Title: Re: Look before you ask
Post by: CNE Runner on February 13, 2012, 10:57:15 AM
Poliss - very handy website (or gadget if you are running Windows Vista [poor sods] or Windows 7). One question though: My research has lead me to believe the CV-29 value for DC (analog) operation was '6'. According to the CV-29 calculator it is '4'. Which is correct for a Bachmann GP-35? [OK, Jim're on.]


PS: Wait a minute. I just checked the EZ Command decoder instructional sheet I had previously printed from the Bachmann website. On page 2, there is a chart that indicates the proper CV-29 value for DC and DCC operation is '3'...not what I thought.

Title: Re: Look before you ask
Post by: Jim Banner on February 14, 2012, 10:26:59 AM
DC conversion on or off is a little more complicated than a single number.  CV29 can have any value from 0 to 255.  But the value is always the sum of certain numbers, namely 1, 2, 4, 8, 16, 32, 64, and 128.  A value of 6, for example, can only be made of a 4 plus a 2.  Likewise a value of 34 can only be made from a 32 plus a 2.

So what do these numbers mean?

1 = reversed normal direction.  Otherwise, front is forward.

2 = forward light control.  For most applications, it will be present.

4 = dc conversion enabled.  Otherwise, DCC only.

8 = bidirectional communications (rarely used).

16 = use speed table.  Otherwise, use Vmax, Vmin and Vmid

32 = four digit addressing.  Otherwise, two digit addressing.

64 = not used at this time

128 = auxiliary decoder.  Otherwise, normal decoder.

So, if CV 29 has a value of 6, it must be made up of 2 plus 4.  The 2 is always there.  The 4 means the locomotive can run on dc as well as DCC.

A value of 3 in CV29 is 2 plus 1.  Again, the 2 is always there and the 1 means the locomotive operates backwards (a command to run it forward will instead run it backward.)  But note that there is no 4 this time.  This means this locomotive is programmed to ignore dc and will only run on DCC.

Give it a try.  What would a value of 51 in CV29 mean?  The answer is down below.

You can also use these numbers the other way around to come up with a value for CV29.  For example, if you wanted 4 digit addressing and no conversion to dc, you would select 2 (because it is always on,) plus 32 (to get 4 digit addressing.)  Added together would give you 34, the value you would program into CV29.

If you don't like this method of finding the value for CV29, print out the table on page 34 of this decoder manual: (


Answer to the question:  if you said the locomotive was using a 4 digit address and running reverse normal and using a speed table, you would be right on the money.  Bonus points if you added that it was running only on DCC.

Title: Re: Look before you ask
Post by: CNE Runner on February 14, 2012, 11:22:00 AM
Jim - Love you as I do, I have to say you could have a bright future in Washington, DC. I read your reply several times - and still have little clue as to what you are trying to impart. For those of us with a PhD, you need to simplify your discussion (...or maybe it is just me).

OK, referring to the chart on the Bachmann website at ( (on page 2), we see the values for CV29. Going across the second chart down on the page, we come to "Operation on digital and analog" in the seventh column over from the left. At the head of this column, it lists a 'bit' number of 3 (and a default value of '1'). I assume (there' that ugly word again) that setting the CV29 value to '3' will restore operation on DCC and DC.

Compounding the understanding of this problem is the heading of this particular chart - which lists the factory default value for CV29 as "decimal 6"...whatever the heck that means. [I guess that would be 06?]

Putting it another way: I guess I'll have to call the Bachmann service center and have a [hopefully] understanding tech 'walk' me through the procedure. Internally, I just know the process can't be that hard.

As always thanks for the reply Jim. [I guess the forum has figured out that electronics aren't my best suit.]


Title: Re: Look before you ask
Post by: Jim Banner on February 14, 2012, 11:16:26 PM
Sorry, Ray.  I tried to keep the term "bit number" out of the discussions because Lenz/Bachmann number the bits from 1 to 8 while the rest of the world number them from 0 to 7.  Just to make matters worse, the wacky wizards number the bits from right to left even though just about everything else in the world is numbered from left to right.  Strange people, these electronics geeks and computer nerds.  And I are one of them.

Okay, I have given my head a good shake, and the bit numbers and binary values are temporarily gone.  So how do we figure out what we need to put into CV 29 to make the decoder do what we want it to do?  The easiest way is to refer to a look up table such as the one on page 34 at this link: (

There are five things you have to decide:

(1) do you want to use 14 speed steps or 28/128 speed steps?
(2) do you want to use a speed table?
(3) do you want analog mode (dc) turned on or off?
(4) which way do you want to operate the locomotive, forward or reverse?
(5) do you want to use a 2 digit or a 4 digit address?

The number you put into CV29 depends on all five of these things.  Depending on which combination of these things you want, the number you put into CV29 can be any one of 32 possible numbers.  Sixteen of these numbers will turn dc mode on.   The other 16 numbers will turn dc mode off.  You find the number you have to put into CV29 by looking in the left column next to the combination of things you want.  (Ignore the numbers with an X in front of them.)

A very common combination is 18/128 speed steps, no speed table, dc mode on, forward operation and 2 digit address.  Looking at the chart, this gives 006.  So to get that combination, you put a 6 into CV29.

An equally common combination is 18/128 speed steps, no speed table, dc mode on, forward operation and 4 digit address.  Again looking at the chart, this combination gives 038.  So we would put 38 into CV29. 

It does not matter what brand of decoders you are using, that chart still works.

The bottom line is that there is no one number that you put into CV29 to turn dc mode on.  But 6 and 38 are probably the most common, the difference between them being whether you want to use a 2 digit address or a 4 digit address.  If the locomotive were a diesel that you wanted to run backwards in a consist, the corresponding numbers would be 7 and 39.  The four numbers, 6, 38, 7 and 39 will cover 90% of the cases where you want dc mode turned on.

Jim  (now gathering up those bits, bytes and geeky numbers that are scattered about the room.)

Title: Re: Look before you ask
Post by: CNE Runner on February 15, 2012, 11:12:26 AM
Thanks for taking the time to answer my question Jim. looks like I need to input a CV29 value of '38' into the GP35. This will give me all the parameters I need AND 4-digit addressing (I like to use the engine # - which is 4-digit).

I want you to know that I reread you first explanation at least six or seven times (as well as reading it to my wife - who is a retired 'legal person'). The reading to my wife helped the most; as she frequently asked me questions on the meaning of each sentence...forcing me to break your explanation down into pieces - instead of trying to 'wrap my head' around the whole thing.

This whole incident reminded me of my years as a part time flight instructor. I always tried to use 'cockpit time' as an additional instructional opportunity (one has to be careful here as the student is in an extreme state of stress). One of my favorite questions was: "What is the function of the propeller?" The student would usually try to impress by talking about a wing on its side producing thrust blah, blah, blah..." After listening to this discourse, I would allow a few minutes of silence before adding; " keeps the pilot cool." The intercom would remain silent for a while before the student would say; "That can't be right...we are in an enclosed cockpit!" I would answer: "While what you say is him sweat when it stops." End of discussion.

Anyway, thanks for the explanation and I will see what results I get after I hook up my MRC Prodigy Advanced system to a piece of test track and check the values on that locomotive.

By the way Jim; the temperature is expected to get into the lower 60s in Alabama today...are you guys swimming yet in Saskatoon?


Title: Re: Look before you ask
Post by: CNE Runner on February 16, 2012, 07:15:22 PM
I thought I'd get back to everyone on the status of my GP35 reprogramming. After digging out my MRC Prodigy Advanced unit (and reading the instructions - since it has been several years away from DCC), I was easily able to program CV29 to '006' (or as Jim would say; "2 + 4"). I checked the running characteristics on the Monks' Island main (DC mode) and the engine preformed flawlessly (albeit looking a little ridiculous on such a small layout).

Thanks to Jim Banner and everyone for helping me out of my problem.