Hornby Class 37 TTS decoder 'overheating'?

[Cyberspice]

Hi all,
 
I've fitted a Hornby TTS sound decoder for a class 37 in to a Bachmann class 37 with the 21 pin socket. I did it by removing the the 8 pin connector and soldering it on to a 21 pin break out board. I also swapped the speaker for one that fits in the space. However its misbehaving. It looks fine and then after a while the sound stops, the loco goes on full speed, and always goes in the same direction. I looks like the decoder is crashing. I can explain the full speed as the H-bridge on the decoder is stuck so the rectified current from the track is being passed straight to the motor.

I have tested using a new, latest version, Bachmann 21 pin decoder and the loco seems fine. It also seems find when I don't use sound so I'm wondering whether its current draw issues. The replacement speaker is supposed to be 8Ω but may be it isn't.

I am an embedded engineering working in mainly software but with some hardware so can do electronics and diagnostics and code and micro-controllers.

 

Any ideas?

Thanks

 

Mel

 

[Phil S]

Did you heck the current consumption of YOUR Bachmann class 37 before fitting a decoder?

 

If the current is close to the capacity, or above that of the chosen decoder - consider a 2nd silent decoder for the motor and lights.

Ensure you have NOT wrapped the TTS decoder in insulation (that doesn't conduct heat),and that when the body is fitted again,there is no short or partial short to motor lighting or chassis ??

 

Did you test run it before soldering via a simple plug in adapter ?

[Paul80]

Greetings

 

First post here so excuse me if I have misunderstood your problem

 

I have fitted a few Hornby TTS Decoders to Bachmann Locos and found the following issues.  (1) don't insulate them with heat shrink or Kapon tape, they don't like being enclosed even using a bit of loose fitting heat shrink is no good as they get hot enough to shrink it, put insulation underneath it on the chassis.  (2) I also found that the Resistors used in the Bachmann lighting circuit to be not enough for the TTS decoder and always put a 1kohm resistor in the blue wire from the decoder.  Once I started doing this I have had zero issues with them and have used them in both 00 gauge & N-gauge without issue.

 

Hope this has been of some use.

[RAF96]

Greetings

 

First post here so excuse me if I have misunderstood your problem

 

I have fitted a few Hornby TTS Decoders to Bachmann Locos and found the following issues.  (1) don't insulate them with heat shrink or Kapon tape, they don't like being enclosed even using a bit of loose fitting heat shrink is no good as they get hot enough to shrink it, put insulation underneath it on the chassis.  (2) I also found that the Resistors used in the Bachmann lighting circuit to be not enough for the TTS decoder and always put a 1kohm resistor in the blue wire from the decoder.  Once I started doing this I have had zero issues with them and have used them in both 00 gauge & N-gauge without issue.

 

Hope this has been of some use.

I agree with the extra resistor. I have had to do the same when using Express Models lighting kits. The motor output of a TTS decoder is self protecting but not the function outputs so the output currents need to be kept within specified allowable limits. The other thing to watch if you change the speaker is to keep at 8-ohms to avoid overloading the sound amp.

Rob

[NIK]

Hi,

 

Its sounds like overheating. I don't think I've tested the current consumption of a Bachmann class 37 chassis.

 

As other contributors have said adding insulation round the decoder and excessive current draw from lights could take it over the top temperature wise.

 

One thing for the future is to test the current consumption of a loco chassis before selecting a decoder to go in it.

 

As an example of what can go awry the Hornby TTS decoder for its HST has a maximum motor current of 500ma yet my Hornby HST chassis draws 600ma worst case. Maybe 100ma is the lights but if they are LEDs its unlikely.

 

Regards

 

Nick

[Cyberspice]

Did you heck the current consumption of YOUR Bachmann class 37 before fitting a decoder?

 

If the current is close to the capacity, or above that of the chosen decoder - consider a 2nd silent decoder for the motor and lights.

Ensure you have NOT wrapped the TTS decoder in insulation (that doesn't conduct heat),and that when the body is fitted again,there is no short or partial short to motor lighting or chassis ??

 

Did you test run it before soldering via a simple plug in adapter ?

Yes, I checked the current consumption, on paper.

 

Yes I did check it with a plug in adapter however the body wouldn't fit so I ran it with the lid off. May have been cooler. When I ran it with the lid off it did not have insulation.

If its this borderline I wont be using it...

[Cyberspice]

I agree with the extra resistor. I have had to do the same when using Express Models lighting kits. The motor output of a TTS decoder is self protecting but not the function outputs so the output currents need to be kept within specified allowable limits. The other thing to watch if you change the speaker is to keep at 8-ohms to avoid overloading the sound amp.

Rob

 

I had thought the speaker I was using was 8 ohm but I'm not so certain now. So I'm going to try with a different speaker that is 8 ohm. Overloading the sound amp could explain what's going on. It seems to be okay unless I push the sound effects.

[Marcyg]

My A4 chip gets real hot. I think it may be because I shorted the speaker at some point and fried the amp. The loco has no lights or other gizmos but even standing still it gets too hot to touch. When the sound on your loco starts to muck around, does it cut in and out like someone with real bad phone reception? My 37 sound chip on the other hand is fine and works perfectly and I've hammered the sound on that.