Keep-alive destroyed decoders.

[saddler]

Hi Folks,

This is my first actual post and is a plea for some knowledge, or maybe a warning to others.

I recently tried to 'improve'   Mainline class 42 by adding a generic home made keep-alive. After finally identifying the negative connection to solder to I gave it a try with a Hornby R8249 decoder. It worked well and I gave it a quick 'body-off' test run, vastly superior to before. Cue cheers and champagne etc.

However when I retried it later the thing was dead. I suspected I may have shorted something when retrieving it from the track. (I tried the decoder after on a test bed..it's knackered).

Trying to be positive this weekend I tried again(more carefully) with another decoder. All was well till I gave it a retry before buttoning it up, dead again. I suspect decoder blown also. This is getting to be expensive. Any clues as to why this is happening anyone?

[Izzy]

Hello Saddler,

 

I will try and answer as best I can. Those with more knowledge may not spot this post as it's not in the DCC section, although hopefully they will.

 

I have fitted home-brew stay-alives to Hornby TTS decoders, which use the R8249 as the basis of them, and have encountered no trouble. These have been ones produced using ordinary 25v electrolytic capacitors, and 16v Tantalums. They have not been 'large', 2,500uf for the former and 880uf the latter, just enough to keep the wheels turning. They both used 100ohm resistors with the Tantalums also having a 16v Zenner for over-voltage protection.

 

As the stay-alive has been common to both your attempts I would suggest double-checking it's construction might be the first step. With these Hornby decoders, as with many other makes, you must turn off DC running ability for them to work properly. It is also the case that once added you cannot 'read' them on a program track. Any programming must be POM.

 

Here is a link which gives details of stay-alive connections for the TTS. It might help with the basic R8249.

 

ttps://www.rmweb.co.uk/community/index.php?/topic/144642-Hornby-tts-stay-alive-solder-connection-points/&tab=comments#comment-3557102

 

 

[saddler]

Thanks Izzy, 

I've been using a 4700uf cap with a 1N4001 diode and 100ohm resistor.

I don't believe I can turn off DC (I think) as I've only got a Hornby Select.

Ps: I not sure what POM is? What's bugging me is the fact that it initially worked in both cases.

I'm not sure if I can bump the post to the DCC section.

Cheers

Nigel

[ITG]

10 minutes ago, saddler said:

Thanks Izzy, 

I've been using a 4700uf cap with a 1N4001 diode and 100ohm resistor.

I don't believe I can turn off DC (I think) as I've only got a Hornby Select.

Ps: I not sure what POM is? What's bugging me is the fact that it initially worked in both cases.

I'm not sure if I can bump the post to the DCC section.

Cheers

Nigel

POM = programme on main, as opposed to on a programming track.

[jcm@gwr]

19 minutes ago, saddler said:

 

I'm not sure if I can bump the post to the DCC section.

Cheers

Nigel

 

If you 'Report' your own post to the moderators, asking them nicely, they can normally oblige.

[Izzy]

Turning off DC running. Not sure whether you can write cv's with a Hornby Select, but if the loco uses a short address just write cv29 with a value of 2, or if it's a long address 34. Full details on cv29 here:  http://www.2mm.org.uk/articles/cv29 calculator.htm

[RAF96]

If your Select is v1.5 or below (startup screen shows <15-30-03)  you can have it updated by return to works Hornby for £15, then you will be able to write to CVs. Call them for a returns number before sending.

[saddler]

1 hour ago, RAF96 said:

 

8 hours ago, Izzy said:

Turning off DC running. Not sure whether you can write cv's with a Hornby Select, but if the loco uses a short address just write cv29 with a value of 2, or if it's a long address 34. Full details on cv29 here:  http://www.2mm.org.uk/articles/cv29 calculator.htm

Hi Izzy,

I'm pretty certain you cannot write cv's with a Hornby Select, however there is a section in the manual about 'switching  analogue mode on/off' which might be the same thing?

Also today I noticed a loco on a siding which was there when I set up the KA loco. It's ok after being re-allocated. Can't see that blowing the decoders up though( I retried them today with no joy). 

I loathe to risk any more decoders till I have more information.

Cheers.

[saddler]

1 hour ago, RAF96 said:

If your Select is v1.5 or below (startup screen shows <15-30-03)  you can have it updated by return to works Hornby for £15, then you will be able to write to CVs. Call them for a returns number before sending.

Could be difficult as I've hard wired it with a switch when the power plug went faulty, they probably wouldn't touch it. Good call though.

[LNERGE]

I think i had a similar encounter. It worked beautifully for a few days. Suddenly it took off like a scalded cat then expired totally. I'm sure the root cause was my failure to adjust cv29.

[saddler]

I think I'm resigned to either writing the loco off or adding pickups to the other(motor) bogie.(although it should be traction tyred.

Or maybe get a controller that does CV's and try a decoder that's more KA friendly.

The joys of RM eh

[RAF96]

18 hours ago, saddler said:

Hi Izzy,

I'm pretty certain you cannot write cv's with a Hornby Select, however there is a section in the manual about 'switching  analogue mode on/off' which might be the same thing?

 

 

Switching off the controller’s ability to control a DC loco is not the same as switching off DC running in a decoder via CV29. 

The former prevents  you from selecting loco zero i.e. an analogue loco.

The latter alters the way a DCC decoder reacts when it loses the DCC signal and thinks it is seeing DC potential. Unfortunately what it actually feels is the full DCC +/- 15volts and away it goes flat out. Adjusting CV29 makes the decoder blind to this, so if it loses the signal then it carries on doing what it was told to last until it hears different from a valid DCC command.

[Sir TophamHatt]

Perhaps post a photo and list of components of your Stay Alive?

Just to make sure the problem isn't there.

 

I've carefully added just one home-made stay alive to a loco.  Doesn't look like it's made any real difference as the motor turns very slowly but the lights stay on for over 30 seconds.  Mine is very large, well over 4700uF as I wanted something that would run for at least 30cm (yes, aware of the dangers but this loco is very old and despite rebuilding the electrics, is still not that great with picking up).

[Osquin]

It might be of interest for me to report here (my first post) that over the last couple of weeks I have (unexpectedly) had success in repairing a couple of Hornby decoders that I blew up in my first experiment with building and fitting stay alives (one died after wiring the wrong way round, the other after an inadvertent short between the track and the motor connection).  Turns out that what fried was a couple of the tiny (I think they are called surface mounted devices, SMDs) diodes that make a bridge rectifier on the decoder board.  Since I was anyway soldering the stay alive connection to one contact of these bridge diodes I thought I’d try to replace them.  Found some equivalents for the 1N4001 online, it was a very fiddly soldering job, but much to my amazement both the fried decoders now work again.  Not sure how much I saved in the time vs cost of replacement equation, but it was kind of satisfying to have experimented and succeeded!

[Grovenor]

Congratulations, not often we hear from someone who has succeeded replacing components on a decoder.

[KingEdwardII]

1 hour ago, Osquin said:

it was kind of satisfying to have experimented and succeeded!

Indeed - there are many aspects to a hobby that are like this - the sheer satisfaction of succeeding to do something tricky is one of the big reasons for doing the hobby in the first place. Hang the cost in terms of time and money!

 

Well done first for understanding what had happened and then for having the skill and patience to complete a fiddly task successfully!

 

Yours,  Mike.

[LNERGE]

I have just fitted three more chips with homemade stay alives. All good so far.

[Sir TophamHatt]

16 hours ago, LNERGE said:

I have just fitted three more chips with homemade stay alives. All good so far.

 

Do you have a list of your components? And any photos? 

[LNERGE]

My methods and components may not be the best. This one is made using Zimo Tantalums. There are four in parallel. Each is 220uf. The resistor is 68 ohms. The diode is from the bits box. I’ve only built one like this and it wasn’t big enough to make much difference to an old Mainline class 03. It was replaced by a more conventional 2200uf can type capacitor that just shoehorns into the 03 cab. I usually use a 100 ohm resistor with that sized cap. 

Edit to add. This capacitor was put into a Hornby Railroad Jinty that was a gift for taking out a subscription to a certain railway modelling magazine. It has made a significant difference to performance. 

Edited March 13, 2021 by LNERGE

[LNERGE]

There is no way this would have negotiated this bit of track before without a cough or stutter..

 

https://www.flickr.com/photos/32297024@N08/51032805362/

[saddler]

This is my effort, worked well on the Mainline Warship till it gave up. Cap is 4700uF, diode 1N4007 and 100r resistor.

 

Incidentally I was quite chuffed when I managed to replace the traction tyres with heat shrink. Not had chance to try it yet.

[saddler]

As a PS to this post I've splashed out on a Sprog programmer and have changed the CV29 values. Might give it another go now.

I wonder if anyone makes a decoder with a negative connection pad to solder to?

Edited March 20, 2021 by saddler
Typo

[Lemmy282]

Try looking at the range from Zimo. Their cheapest is about £20 and has negative a connection pad at the edge of the board.

 

Nigel L

[RAF96]

On 20/03/2021 at 20:43, saddler said:

As a PS to this post ...

... I wonder if anyone makes a decoder with a negative connection pad to solder to?

 

Strathpeffer shows two ways of connecting a stay alive to a Hornby decoder, via the diode pads or via more easily accessible pads at the sides of the decoder. See his site for details.

[saddler]

II've just bought two decoders from Lais DCC they have the leads for KA already attached. Will try one with that Warship next week. Will report back.