No sound on RTR

[Garside]

I have bought a class 121 by Dapol from Hattons , a very nice model and after cleaning the wheel treads runs very smoothly and the lighting is very controllable via F numbers but there’s no sound! its 0 gauge by the way.

Has anybody had the same problem and if so what was the answer? I can’t have it replaced as Hattons do not have any more someone bought the last one shortly after me. It’s a nice model and still good value so have decided to keep it just need to find whoever installed the chip and if they can spead any light on what’s likely to be the answer to the fault.

 

regards Mike 
 

[Ray H]

Is there a loose wire that should go to the speaker?

 

Can you test the decoder in another vehicle and/or with a different speaker?

[Nigelcliffe]

Qu1 - are you certain it's got a sound decoder and speaker inside it ?   There have been mistakes/mislabelling in the past, and that's a £100+ difference if you haven't got the sound decoder.   
Either a visual check, or many can be identified from programming track - reading various CV's can give make and model of decoder to high precision.  Other decoders may be vaguer.   JMRI (if you have it) will help with this. 

 

Qu2 - Try various functions to turn on sound.  Usually F1.  Some things might be F8.   

 

Qu3 -  As per Ray's suggestion - Is the speaker actually connected ?  

[Hroth]

Was it sold as sound fitted, or just as DCC fitted?

 

 

[Garside]

It was sold as sound fitted. It has a Zimo MX644C chip in it and I have checked all of the connections to all three speakers and have done a reset which changed the address back to 3.

regards Mike 

[Nigelcliffe]

I'll assume a positive identification of a MX644C  (can be checked by reading back CV8 (will read back as 145 for Zimo) and then CV250 should read "222" for a MX644).
 

 

Then, look at the sound CV's.  

Start with volume, CV266.  Ought to be "sensible" - say 40 to 70.   If zero, increase to around 50.  

Then Sound Project, CV265.  For a diesel it is likely it is "101".  If it has value "1" then that's set as a "steam" project, and may be the issue.  

 

CV310 defines the key for sounds on/off.  See what value it is set to, and use that function key to turn sound on/off.  

CV311 might be useful on diagnostics.  That sets whether function key sounds require another key (sound on/off) to work.  Read the value, note what it is (to put it back), and try changing to zero.   That should enable sounds to play on function keys without the main engine noises - will show the sound decoder is operating.  

 

 

Lack of documentation around who supplied the sound project is going to hamper things somewhat.   

 

- Nigel

 

 

[Ray H]

I wonder if having three speakers might be the problem as the wrong impedance mix could cause problems.

[Garside]

Ray they are all the correct size. 
Nigel, thanks for the information I will check tomorrow, I have done CVS 266 & 265 266 is 64 but I think 265 is set at 0 so will change to 101 and hopefully that’s the problem!

 

regards Mike 

[WIMorrison]

28 minutes ago, Garside said:

Ray they are all the correct size. 

 

Does this mean the 'correct' physical size, or the 'correct' resistance value, and if the 'correct' value is that the 'correct' value as written on one speaker? Also, are the speakers connected in series or parallel?

[jamesed]

Just in case it's helpful to some people reading this post, let's have a little science lesson.  The impedance of loudspeakers used, or the cumulative impedance where a series of loudspeakers is used is very important. 

 

The MX644 can output into 4-8 Ohms so that's the range the overal impedance needs to be.

 

Impedances where speakers are wired in parallel are calculated as:

If all speakers are the same impedance simply divide the impedance of one speaker by the total number of speakers in the circuit.

For speakers wired in series:

r+r+r etc. 

So, for example, two 8 ohm speakers wired in parallel would have an overall impedance of 4 ohms (8÷2) but if you wire the same two speakers in series then it will be 16 ohms (8+8).

 

Most model railway speakers, designed to be used with dcc sound chips, are 8 ohms.  So, if you are using just one speaker or two speakers wired in parallel then that's fine for a decoder with a 4-8 ohm output.  Be careful though as some decoders are 8 ohms only so make sure you check the specification.

 

In this case the OP has three speakers which, for the sake of this explanation we'll assume are all 8 ohm impedance.  Now, if they were all to be wired in parallel that would be 2.67 Ohms overal impedance (8÷3) which won't work. If all wired in series it would be 24 Ohms which won't work either.

 

In order to make this work you'd need a combination of series and parallel wiring. If you wire two speakers in series that gives you 16 ohms. Then wire the third speaker in parallel with the first pair and you'll get an overall impedance of 5.33 Ohms which is within the output parameters of the decoder. (The maths to get to that calculation is a little more complicated but there are online calculators available online if you need them). [(1/16 + 1/8) = (1/16 + 2/16) = 3/16 = (1/16÷3) = 1/5.33 therefore impedance = 5.33]

 

Ok, so that's what one should do to ensure it all works fine and it may be that this is exactly what the OP has done.  However, if you were to simply put three parallel wired 8 Ohm speakers into your loco, which as explained above is 2.67 Ohms overall, what would happen.  The amplifier circuit on the decoder board would be over driving the speaker and initially you'd  probably hear a distorted noise. After a while (which could be anything from a fraction of a second to a bit longer) the likelihood is that the amplifier circuit on the decoder board will overheat and burn out. It's also possible that the speakers could be damaged depending upon how long it runs for before the amplifier cuts out.  Professional PA amplifiers have protection circuitry built in to stop this happening and will hopefully cut out before any damage occurs but it seems unlikely that there is room for this on a tiny dcc decoder chip so it's very important to get it right first time.

 

So, to the OP, if you are concerned that what I have described above could be your problem, disconnect two of the speakers and just connect one single speaker to the decoder outputs. If that works then you are ok. If it doesn't then you may have blown the amplifier circuit on your decoder which is probably terminal. 

 

Edited November 4, 2022 by jamesed
typo correction

[WIMorrison]

@jamesed your explanation is why I asked the question - but I thought I would wait until we know what has been done before complicating things, useful though the post is.

[spamcan61]

I was under the impression that the OP had bought the item as DCC sound fitted, so it should work out of the box, and the speakers should be matched to the chip, I would think?

 

Incidentally speaker impedance varies drastically with frequency (factor of 3 or more) , so any nominal speaker impedance is very nominal. Not saying any speaker will work in any situation, but it's not like combining resistor values in practise.

[Garside]

Nigel, I have now checked CV265 and it’s set to 101, CV310 is 1, 311 is 0 hope they’re correct 

I can can confirm that the United was purchased as being with sound and all appears to be wired up correctly, I have spoken to Dapol and they referred me to Hattons who can only refund my money as they can’t replace it! But I think it’s worth keeping it as it’s still good value and cheaper than a DCC fitted one. At the moment I am just trying to find a solution and still have other leads to follow so thanks for helping it’s much appreciated.

 

regards Mike 

[Nigelcliffe]

The CV values seem fine.  CV310 indicates "F1 for sound".  CV311 indicates that horns and other noises should play even with F1 turned off.  

 

As the decision is keep even though not working,  then I'd try the decoder in another loco (or a decoder tester).  

That way isolate "loco problem" from "decoder problem".   

 

If its a decoder problem, then various Zimo retailers may be able to help. 
They could, for a fee, load new sounds to it (it won't be the same sounds as Dapol supplied, but whatever that retailer can offer.   BUT, if its a decoder fault, I'd be concerned the sound output has failed - in which case check the loco wiring and speakers very carefully before they damage another one). 
There is a Zimo repair/return system (replacement decoder at a very good price when one is damaged), though quite how that would work for a decoder not purchased from one of the retailers is not clear.

 

 

- Nigel

[Garside]

Nigel I have come to the conclusion that although I think the wiring is OK tomorrow I will dismantle the loco completely and examine it with a large magnifying glass and make sure there’s no soldier joints that have “whiskers “ and caused a fault also any crossed wires but I think the wiring is OK as it’s well laid out and I did look at it carefully. I think I can’t try the chip in another loco as I think the two I have maybe plux18 socket! I will have to take the bodies off to find out.

Thank for your time and help it’s much appreciated.

regards Mike 

[nick_bastable]

when my C lost its voice youchoos  advised me after they reset it   as   follows Zimo factory values (possibly CV#8=0 or CV#8=1 for example).  I reset using CV#8=8   which restored the sound project

 

hence why my C ran at Derby sans voice working fine now

 

Hope that helps

 

 

 

[Garside]

Nick reset using CV8=8 was the first thing I did, but it had no effect, to everyone else I have now checked the wiring using a strong magnifying glass and have not found any faults, most of the distribution is via a pub so mainly short connections and couldn’t see any soldering whiskers that’s usually the problem.

Thanks all for your information and comments

 

regards Mike 

 

[Ray H]

Some Zimo decoders use F27 & F28 to adjust volume up and down. Might it be possible that this decoder has had the sound turned down to zero or turned up too high that it damaged the decoder as happened to one of our club members.

[WIMorrison]

And f14 to mute the decoder completely

Edited November 7, 2022 by WIMorrison
spelling :(

[pauliebanger]

14 hours ago, Ray H said:

Some Zimo decoders use F27 & F28 to adjust volume up and down. Might it be possible that this decoder has had the sound turned down to zero or turned up too high that it damaged the decoder as happened to one of our club members.

 

14 hours ago, WIMorrison said:

And f14 to mute the decoder completely

 

This information may not be correct in all cases. It will depend upon the sound project. Always best to view the information provided by the supplier, often in the list of functions or however it is described.

 

The volume down and volume up adjustment can be assigned to any key. I began using F27 (CV396) and F28 (CV397) as the defaults in my sound projects for Digitrains based on the frequency of need to adjust overall volume. Other creators have since either followed this, or assigned the same keys based on the same logic, so it has become something of a de facto normal setting.

 

But there are ZIMO sound projects (some of which were created by me) which use different keys for overall volume adjustment (or omit the feature altogether). Manufacturers' and commissioners' requirements vary.  As Ray H correctly pointed out - 'some ZIMO decoders use F27 and F28'

 

Any creator worth their salt will avoid inadvertantly triggering dangerously high volume levels by fixing a 'Max overall volume' available via the assigned 'increase key'. This is done by setting CV395 at a 'safe' value. Of course, any operator is able to increase the value in CV395 to dangerously high levels, or use the actual maximal overall volume CV, which on ZIMO is CV266 to over-rule project defaults.

 

The mute control is also freely assignable. (CV 313).  I mainly assign this to F19 (because when I started creating ZIMO sound projects, this was the highest value F key available) but any key assignment is possible. Indeed, some projects do not have the feature enabled at all. The SLW Class 24 does not have the mute function as F27 and F28 can adjust volume in real time and the project is so packed with manufacturer's required features that there was simply no free F key available for it.

 

Best regards,

 

Paul