The Curious Case of a Zimo 638D 21-pin MTC decoder and a Dapol Class 121

[geoffers]

The Facts - (1) a OO Dapol Class 121 which was tested on DC and all lights worked.

(2) needs a 5-function decoder so went the whole hog and bought a Zimo 638D 21-pin MTC 6-function decoder.

 

The Crime - Lights on F0, F1, and F2 work but not compartment lights on F3 despite them working on DC.

 

The Question - Dapol recommend their own 5-function Imperium decoder. Is there a problem with installing a 6-function decoder? Is there some fiddling I need to do with the Zimo decoder?

 

Now this is not the end of the world and I can live with this but I could have used a bog-standard 4-function chip already in my bits box rather than go to the expense of buying the Zimo chip to get the same results.

 

Any suggestions please. Until then the Jury is out.

[geoffers]

Sorry - I should have said Zimo MX638D.

[Nigelcliffe]

The 21 pin socket is a bit of a mess standards wise - there are two versions of the standard (oh joy!). 

The first four outputs are fine (front light, rear light, output 1, output 2), those are all normal full-power outputs.  The problem is the outputs 3 and 4, which can be either full power or logic level. 

 

The following from reading the documentation - I don't own a 121.  But the documentation implies a CV change could fix things:

 

 

First question to Dapol:  which version of 21pin, "logic level" or "full power" ?  I can't find an online instruction sheet for the 121.  Dapol's instructions for the Imperium decoder says "Aux 3,4,5 & 6 are Logic level outputs".   As that's the decoder Dapol would recommend, it implies that the 121 is expecting "logic level" for output 3. 

 

Zimo cover both versions of the 21-pin standard.  They use the designation "C" for logic level and "D" for full power on the 21-pin decoders.

The MX631D is "wrong decoder", that has full power on outputs 3 and 4, you need the MX631C which has logic level on outputs 3 and 4. 

The MX634D and MX638D decoders can be changed between the two different 21pin standards by a CV change.   CV8=3 gives logic level on outputs 3 and 4 (what appears to be required for the Dapol 121) and CV8=4 gives full power outputs (as shipped condition for MX634D or MX638D). 

 

So, a documentation hunt says a CV write of CV8=3 will change the Zimo MX638D to provide logic level output. 

[beejack]

Try a Lenz Silver + 

 

All lighting works although I have reconfigured mine.  I have directional on F0, Cab lights on F1 and Interior lighting on F2.

 

If I remember correctly, the cab lights were on F1 and F2 and the interior was on F4 or F5. 

 

I used JMRI Decoder Pro to reconfigure the chip so that the cab lights are only on in the direction of travel but remain switchable this meant I could group the lighting together. 

 

I did try a Bachmann 56-554 and 56-557 but with one function missing the interior lights remained on 

[geoffers]

Wow! Excellent advice. Thanks a mill. Will give a recon a go.

[geoffers]

This is what I love about this forum. Advice and help is freely given. Reconfigured CV8 to 3 (it was 145) and - voila - the compartment lights work. Thanks again.

[Nigelcliffe]

This is what I love about this forum. Advice and help is freely given. Reconfigured CV8 to 3 (it was 145) and - voila - the compartment lights work. Thanks again.

 

Glad it worked.

 

However, if you try to read CV8, it will still read 145.  CV8, like CV7(* below), is an odd-ball CV.  In Read CV8 ALWAYS reports manufacturer number, 145 = Zimo.

 

What Zimo are doing is using CV8 as a write-option to change configurations of the decoder, so there will be several different "resets" available (depending on exact Zimo model) and, in this case, an option to change its output behaviour to cope with the silliness caused by two different 21-pin standards. 

 

 

(*  CV7 will report the first part of the firmware version number.  If some other CV's are read, a Zimo will report the full decoder firmware (eg. 37.2, or whatever) and the hardware identity (a number which means you can look up its a MX638, and not an MX634 or something else...).  )

 

 

 

- Nigel

[geoffers]

Thanks again NigelCliffe. Advice was spot on. Interesting info on CV7 and CV8 and I was totally in ignorance on that as well as the two standards for 21-pin decoders.

[philg]

On 11/10/2018 at 09:17, Nigelcliffe said:

The 21 pin socket is a bit of a mess standards wise - there are two versions of the standard (oh joy!). 

The first four outputs are fine (front light, rear light, output 1, output 2), those are all normal full-power outputs.  The problem is the outputs 3 and 4, which can be either full power or logic level. 

 

The following from reading the documentation - I don't own a 121.  But the documentation implies a CV change could fix things:

 

 

First question to Dapol:  which version of 21pin, "logic level" or "full power" ?  I can't find an online instruction sheet for the 121.  Dapol's instructions for the Imperium decoder says "Aux 3,4,5 & 6 are Logic level outputs".   As that's the decoder Dapol would recommend, it implies that the 121 is expecting "logic level" for output 3. 

 

Zimo cover both versions of the 21-pin standard.  They use the designation "C" for logic level and "D" for full power on the 21-pin decoders.

The MX631D is "wrong decoder", that has full power on outputs 3 and 4, you need the MX631C which has logic level on outputs 3 and 4. 

The MX634D and MX638D decoders can be changed between the two different 21pin standards by a CV change.   CV8=3 gives logic level on outputs 3 and 4 (what appears to be required for the Dapol 121) and CV8=4 gives full power outputs (as shipped condition for MX634D or MX638D). 

 

So, a documentation hunt says a CV write of CV8=3 will change the Zimo MX638D to provide logic level output. 

Sorry to resurrect an old thread, but I’m looking to replace the bubblecar supplied Dapol (LAIS DCC (TCS clone/ripoff)) decoder with a Zimo MX638D but I can’t find any Zimo documentation that talks about switching F3/4 to logic level - which the bubblecar requires

 

could someone perhaps remember where they found it before I commit

 

Thanks

 

Phil G

[jpendle]

Zimo Small Decoder manual

Section 3.3, page 15

 

CV #8 = “3”  Converting a MX634D to MX634C

CV #8 = “4”  Converting a MX634C to MX634D

 

Regards,

 

John P

[philg]

1 hour ago, jpendle said:

Zimo Small Decoder manual

Section 3.3, page 15

 

CV #8 = “3”  Converting a MX634D to MX634C

CV #8 = “4”  Converting a MX634C to MX634D

 

Regards,

 

John P

Must be missing it

 

I'm at http://www.zimo.at/web2010/documents/Small_Decoders.pdf and looking at section I see they describe pseudo programing CV sets, but nothing about logic level function outputs nor setting CV8 to 3 or 4 (or is there any reference to MX634C or D anywhere in the doc)

 

Is this ability still  provided??

 

Is there a different manual for the 634 or 638 decoders??

 

AHA!!!!

 

There's anther small decoders manual at http://www.zimo.at/web2010/documents/MX-small-decoders_EN.pdf

 

Much appreciated - time to investigate Zimo decoders methinks

[Nigelcliffe]

The software in Zimo decoders are updated very regularly (and can be updated by the owner if a new feature is needed).   The German manual is usually close to the updates, the English somewhat behind, but is updated.  

 

Zimo manuals listed on the maker's website from here: 

http://www.zimo.at/web2010/documents/handbuch.htm

 

These models fitted with the MTC-21 plug are swappable between "logic" and "full power" versions, to allow both versions of the 21-pin standards:  MX634, MX636, MX638.   Described in the German language version.  

 

 

[LNERGE]

Ah the answer to one of life’s great mysteries. I thought it wasn’t going to work for me but in my fumblings I’d turned off the lighting via the switch on the chassis. Many thanks.