TTS QUESTIONS

[mkrob]

After having a tts chip going phut, when I removed the supplied speaker & attached an iphone speaker (8 ohm), I'm wondering if I'm taking the right precautions.

1) Using a standard Antex 25w soldering iron  to solder the wires to the new speaker. Is it earthed? Should I use a crimped connection to the speaker to avoid a possible problem with the soldering iron?

2) Should I buy & use an ESD earthing wrist strap,when working on the wiring of tts chips?

3) Has the new speaker got an impedance of 8ohm or possibly less, even if the retailer say it is 8ohm, which could cause the chip's amp to blow because it is being over-driven?

I did get a refund for the duff tts chip, but its made me very wary of changing anything on tts wiring!

To be fair to Hornby,there no quibble years guarantee is excellent, for a good product.    

Any suggestions,apart from buying proper dcc sound chips

 

[Chrisr40]

Hi Mkrob,

 

The static strap is a sensible precaution but to be honest I have never used one and touch wood all TTS that I have fitted to dcc ready and non dcc ready locos have gone without a hitch. I make a point of only handling the chip by its edges and leaving it in the silver static preventative bag for as long as possible. Then applying just one layer of clear tape to the chip and making sure where its located in the loco there is some free space around it for air circulation.

The Hornby speakers are a bit naff so I replace them with an aftermarket source of which there are plenty but I will recommend road and rails just because of good customer service, price and so far 100% quality. I solder the new connections and heat shrink them to isolate. Nothing more involved than that. I will add though I make sure the loco is running freely first as a chip will only accentuate rather than improve a dodgy runner.

 

Good luck with the replacement chip

 

Chris

[RAF96]

1. I use an Antex iron without trouble but you should check there is no potential between the tip of the iron and the earth pin on the plug. Some irons can show a damaging potential across tip to earth.

 

2. Cover  the chip with a single layer of Sellotape either side, then you can safely handle it, else hold it by the edges not the components as Chris said.

 

3. You can measure the impedance of a speaker using the resistance scale on you multimeter.

Edited April 13, 2020 by RAF96

[spice1977]

I had several go pop (TTS). I found that by using kapton tape they overheated so now I only wrap it in kapton tape for whilst i am working on the chip ie changing the speaker etc. I make sure wherever I place the chip that i use kapton tape to make sure its safe to place the decoder, unwrap the tape from around the chip then use some black tack under the wires to hold the chip in place - this means sufficient airflow to remove heat from the chip but it is secured in place - just fitted one yesterday with Richards double iphone speakers wired up with a zimo dumbo in a 66 (my last in stock too so need to buy more!). For TTS or other chips that do not come ready protected I use an ESD wrist strap.

[RAF96]

Another thing I do when soldering speakers is to tape the speaker to the bench as the magnet can attract the soldering iron tip which could touch the speaker cone. 

[mkrob]

Thanks guys,for the advice & suggestions

 

1) Regarding any voltage between the iron tip & earth, there wasn’t any detected. I’m not convinced that the iron could or could not cause a problem,so I think I’ll try a crimped speaker connection in future.

 

2) I think using a ESD wrist strap can’t do any harm, so I’ll use one in future.

 

3) The 8 ohm impedance Iphone speaker measured 8 ohms with my cheap multimeter. I measured a Onkyo 6 ohm speaker at 9 ohm. Draw your own conclusions from that. From what I understand, impedance of a speaker cannot be measured that accurately when measuring with a multimeter anyway.

 

After reading other peoples comments about decoders, it would seem to wise to use a ESD wrist strap when touching them, as with any PCB with integrated circuits on it. As we all know electrostatic discharge can do damage to electronics & not be apparent for some time. It would seem sensible therefore to use a ESD wrist strap whatever electronics is being worked on.