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Heljan 128 fries three decoders


Deborail
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I used a digitrax 166 decoder on my new Heljan 128 DPU and the decoder burnt. The locomotive still runs fine on DC though. I tried with a Dapol Imperium and that too became unresponsive although there was no burning. Both decoders are not accessible on the programming track indicating that they have failed. 
 

Am I using decoders that are not suitable for this locomotive? What sort of current does this locomotive draw? In the picture the burnt hole is visible. 

3E4D06DD-75C6-4B1E-A782-C191F382AF35.jpeg

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I think your loco has a problem. It is, as many of us have been pleased to find, a mighty hunk of motive power, takes no prisoners and could probably pull walls down. I'm not sure which decoder is in mine, since it was bought s/h already chipped, but after a couple of years it is still working fine, and your purchase of this decoder with 1.5 amp capacity and 2 amp peak should have been more than adequate. I use mine to tow a track-cleaning wagon, so when it runs it generally is moving for 15 or 20 minutes to clean everywhere. 

 

On DC does the motor become hot? 

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I realise this does not help the OP but for the amount DCC decoders cost (or rather how much is charged) they should have output protection built in. In other words even if you have a short circuit at the output they should not fry themselves. This protection is available in many voltage regulators (e.g. 7805) that cost less than £1.  A DCC decoder is much more complex and sells in fewer numbers but cost 20-30x as much.  Perhaps the cheap decoders could not have this (you pays yer money an takes yer choice) but to hear that the pricier ones blow is disapointing.

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6 minutes ago, H2O said:

I realise this does not help the OP but for the amount DCC decoders cost (or rather how much is charged) they should have output protection built in. In other words even if you have a short circuit at the output they should not fry themselves. This protection is available in many voltage regulators (e.g. 7805) that cost less than £1.  A DCC decoder is much more complex and sells in fewer numbers but cost 20-30x as much.  Perhaps the cheap decoders could not have this (you pays yer money an takes yer choice) but to hear that the pricier ones blow is disapointing.

 

Quality decoders do have output protection - Lenz, Zimo, etc..     

But, US products don't typically fit such devices.  Gaugemaster DCC products are bought-in devices rebadged as Gaugemaster, some of their decoders are from Digitrax, and some are the common Chinese copy of an old TCS design - both US origins.  

 

Back at the loco, having blown two, I'd be (a) checking the current draw, and (b) putting a multi-meter over the PCB to check that tracks are not connecting "pickups" to "motor leads" when the decoder socket is empty.  

 

 

- Nigel

 

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I have tried to read the decoder and all is reset to zero. I tried to reprogram and that works. Then on the main track no response. Then back onto the programming track reading reports zero again. This means that the decoder resets itself when on the main track. 

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5 hours ago, Nigelcliffe said:

putting a multi-meter over the PCB to check that tracks are not connecting "pickups" to "motor leads" when the decoder socket is empty.  

I have had this problem on an Athearn loco. the track + wire was bridging to the motor + on the motherboard (these 2 connections are joined on the DCC blanking plug so this fault will only become apparent on DCC)

With the blanking plug installed the loco ran fine on DC, when I fitter a decoder it ran ok in one direction but the magic smoke was released in the other direction

Have you tried the decoders in a decoder tester or another loco

John

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Programming the decoder works okay. When it is read then all values are zero. Does this indicate a damaged decoder or bad contacts?

 

furthermore when resetting the CV 8 to 8 the controller says 

 

‘no decoder ACK pulse!’

 

does this mean that the decoder is RIP?

Edited by Deborail
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6 minutes ago, Deborail said:

Programming the decoder works okay. When it is read then all values are zero. Does this indicate a damaged decoder or bad contacts?

 

furthermore when resetting the CV 8 to 8 the controller says 

 

‘no decoder ACK pulse!’

 

does this mean that the decoder is RIP?

 

Can't tell.   Could be anything, but does point to a possible decoder failure. 

 

BUT, if a loco destroys two decoders, it suggests a problem with the loco which should be investigated, as pointed out in previous posting.  It is possible to have a fault which destroys decoders yet gives correct running on DC.    

 

 

 

 

 

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18 hours ago, WIMorrison said:

Dare I suggest that if you are getting values of zero after you have written to to the decoder then writing isn't working - if it did you would read back some values.

You’re right .

 

but I get a message of ‘writing is completed OK’ on the controller. 
 

All the loco lights flash during the writing job. 

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35 minutes ago, Deborail said:
19 hours ago, WIMorrison said:

Dare I suggest that if you are getting values of zero after you have written to to the decoder then writing isn't working - if it did you would read back some values.

You’re right .

 

but I get a message of ‘writing is completed OK’ on the controller. 
 

All the loco lights flash during the writing job. 

 

Disagree with conclusions.   

All you have is "read" isn't working.  Everything zero isn't sensible, it just says something seriously wrong.  Some CV's (eg. 7, 8) should come back with non-zero and non-changing values.   If the motor outputs don't seem to work, that's probably why the readings are nonsense.   

 

You don't seem to have addressed the more basic question as to why a loco can fry two decoders...

 

- Nigel

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Make it three decoders. It has fried a third :angry:one on the programming track. I decided to try one more. Still operates fine with the blanking chip in DC mode though. 
 

Current draw in DC mode is 300 mA tops. 
 

the metal chassis is not electrically connected to the rails. 
 

DSO does not show any abnormal wave pattern. I will try to ask Heljan for help before burning any more decoders. 

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Lift up the PCB, look underneath.

Are the DCC pins insulated, or can they touch the metal of the chassis? Looking at the pin assigments it would be bad news if pin 1 and 22 shorted out, I think pin 1 is a sensor input and my guess is it doesn't take 18V AC

On DC 21 and 22 basically go to 19 and 18 and pin 1 should not be connected - so you would be running okay

Put some insulation tape if the underside of the PCB is naked - it usually is on Heljan, from my experience.

At the same time see if you can spot whether there are any solder bridges between the 21pins - send in a photo why not?

1287682900_dccpinout.jpg.f603fd3e023cd20ebc819790aa08c862.jpg

If I bought that model brand new and it was proven to be defective in normal use - and caused damage to my equipment as a result, I would be asking Heljan to take it back for inspection and I would expect compensation for the damage.

 

In the meantime I would not be installing any more chips

Edited by letterspider
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If you will forgive me I am bemused that a decoder can be fried on a programme track. I have always understood that the only current that flows is of low voltage for the brief duration that a signal is sent, and that the whole idea is that damage can’t occur to a decoder. 
 

Am I wrong?

 

If not then it would suggest that perhaps there is something wrong with the program track configuration. 
 

Izzy
 

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7 hours ago, Izzy said:

If you will forgive me I am bemused that a decoder can be fried on a programme track. I have always understood that the only current that flows is of low voltage for the brief duration that a signal is sent, and that the whole idea is that damage can’t occur to a decoder. 
 

Am I wrong?

 

If not then it would suggest that perhaps there is something wrong with the program track configuration. 
 

Izzy
 

It is also surprising to me that this would happen on the programming track, but it did during the programming of the third blown decoder. And the locomotive did move forward as well. It moved significantly. However I have tested other locomotives and decoders on the programming track and all is normal so I don’t believe there is something wrong in the programming track. 

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7 hours ago, letterspider said:

Lift up the PCB, look underneath.

Are the DCC pins insulated, or can they touch the metal of the chassis? Looking at the pin assigments it would be bad news if pin 1 and 22 shorted out, I think pin 1 is a sensor input and my guess is it doesn't take 18V AC

On DC 21 and 22 basically go to 19 and 18 and pin 1 should not be connected - so you would be running okay

Put some insulation tape if the underside of the PCB is naked - it usually is on Heljan, from my experience.

At the same time see if you can spot whether there are any solder bridges between the 21pins - send in a photo why not?

1287682900_dccpinout.jpg.f603fd3e023cd20ebc819790aa08c862.jpg

If I bought that model brand new and it was proven to be defective in normal use - and caused damage to my equipment as a result, I would be asking Heljan to take it back for inspection and I would expect compensation for the damage.

 

In the meantime I would not be installing any more chips

Thanks for the very eye opening information. I have lifted the PCB which is mildly stuck onto a black plastic surface. I have added a layer of insulation tape just in case. The underside of the pins does not show any soldering overlaps. Pins 1 and 22 do not seem to be shorted. The motor pins 19 and 18 have a suitable resistance between them. All seems very normal. The problem is that to test any further would run me the risk of blowing more decoders. I am getting resigned to the fact that this is destined to become a DC only loco. 

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This does seem to be a situation where you find yourself between a rock and a hard place. I’ve been trying to think this through, and am just wondering if it could be a problem with the motor somehow. Even with decoders that have short circuit protection I think I am correct in that few have motor output protection against short circuits, mainly it’s the other side, DCC track power. This might explain the continual frying of decoders. Under DC the controller might be able to cope with it and the motor turn over. It’s just a thought.
 

Not sure where you’d go from here. Me, I’d be so vexed I’d rip out the PCB & wiring, well remove it for possible re-use if I found the issue, and test with a basic hard wired setup, just the track power to the decoder & feed to the motor. Or perhaps even just take the motor out first and test in isolation. Personally I hate things like this to get the better of me when there must be an answer somewhere. It’s just finding it...!

 

Hope you have better luck moving forward

 

Izzy

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11 hours ago, Izzy said:

If you will forgive me I am bemused that a decoder can be fried on a programme track. I have always understood that the only current that flows is of low voltage for the brief duration that a signal is sent, and that the whole idea is that damage can’t occur to a decoder. 
 

Am I wrong?

 

If not then it would suggest that perhaps there is something wrong with the program track configuration. 
 

Izzy
 

My programming track on my ECoS is permanently live... if I short it, it trips the ECoS out just like main.

 

My ECoS will also allow up to (I think) 500ma I know this because when I read a loco on the programming track rollers that's doing a (dcc runaway) it trips the ECoS out. But with the right fault 500ma is more than enough to blow a decoder.

 

the Heljan 128 does not suffer from the usual build issues that say the Heljan type 2s suffer from, its a better built locomotive, and plastic cover prevents any shorting of the pins on the main PCB.

 

So you have found the motor to be drawing only 300ma, which means the drive train is not overloading your decoder, you have found your PCB is not shorting out...and you have found no stray joints on the PCB.

 

that leaves one possibility

 

A fault in the lighting circuits, (try a cheap Bachmann 21 pin decoder with the lighting circuits unplugged)

 

Does the decoder blow instantly or does it take a short while? because motors faults can manifest after periods of running.

 

does the decoder blow if its run under the default settings on the main? ie without re-programming it?

 

Could be a fault with the programming track as izzy said but it wouldn't it have blown something else by now?

 

 

 

Edited by pheaton
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I have contacted Heljan and they said that their motors need robust decoders such as ESU. I was

told to use ESU. They said cheaper decoders cannot handle the load of the motor on this locomotive. So far the decoders used were digitrax and a couple of Dapol Imperiums 

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