Hornby Class 73 Blowing Chips

[Butler]

Hi

I purchased  a Hornby Class 73 a few years ago, but on fitting a decoder, there was a puff of smoke from the chip, I tried this twice, then gave up! Getting costly. I’m not sure if it was new or not. But I recently decided a 73 would be a good addition, I’m told the Dapol 73 can be troublesome, so thinking about having another go with the Hornby .What should I do, measure the current drain? I don’t have any DC to try it, but guess I could rig something. Any ideas?

B

[pheaton]

Check for shorts, on the dcc socket, caused by Tin whiskers, I would say it was a short on the function side of the decoder as a short on the motor side....should trip the dcc system out.

 

What decoders have you tried ?

[Butler]

Hi

Thanks for the reply, They were both Hattons 8 pin direct, I will take another look at it, i could put the blank back in and rig dc up. Will any 8 pin blank do? All got a bit mixed up in my boxes.

B

[RFS]

Any 8-pin blanking plug will do. 

 

Would be worth investing in a decoder such as the Lenz Standard+ or MX600R both of which have short circuit and overload protection, unlike the Hatton's chip. I've got two 73s with the Lenz decoder and both are fine. Do remove the capacitor (interference suppressor) though. 

[Butler]

Thanks , great, are they Hornby 73’s? How do they compare detail wise to the Dapol? I do like the red Buffer beam, could always repaint the beam.

B

[Nigelcliffe]

Testing a loco which is known to be faulty, by putting in more decoders and hoping they work isn't sensible in my view.   Decoders with some overload protection are not a sure-thing if the loco is faulty.   If there are tenners to burn, perhaps donating them to a charity would be a better use ?  

 

 

Decoders blow for a reason, often it can be traced to an internal wiring fault.  Some of those faults won't show up on DC, but will bite on DCC.   A loco can be tested pretty quickly with a multimeter.    With no decoder or blanking plug fitted,  look for any electrical path from the track pickups (one at a time) with each of the other pins on the decoder socket  (so that's 6 tests per pickup wire, two pickup wires, total of 12 tests).  There should be no circuit in all cases.    If one connects, that tells you where to look for the fault.  

 

 

- Nigel

[Butler]

Thanks Nigel Ok will do, I get what your saying, so the other 2 pins of the socket are the correct ones from the pickups? So I’ll get a reading on 1 pin per pickup, but not any of the others.?

B

[GoingUnderground]

20 hours ago, Nigelcliffe said:

Testing a loco which is known to be faulty, by putting in more decoders and hoping they work isn't sensible in my view.   

Albert Einstein is supposed to have said that insanity is doing the same thing over and over again but expecting the result to be different.

[Nigelcliffe]

All 8-pins are wired this way (or are wired this way if wired correctly :-)  )

 

The image is from above, so looking down onto a decoder socket in a loco, or looking at the back of a decoder plug.   (image from TCS website, TCS being a long established decoder maker )

 

 

With multimeter set to "continuity buzzer" or "resistance", and nothing in the decoder socket in the loco, test the following: 

 

1  Red (pin 8) to pickups.  One should buzz (zero resistance) the other side wheels/pickups should not connect.  It should be to the right hand side wheels, when looking at front of loco. 

2   Black (pin 4) to pickups.  The other side should buzz (zero resistance) compared to test 1.

3   Red (pin 8), in turn to each other pin.  None should buzz.  (ie. all infinite resistance).

4   Black (pin 4) in turn to each other pin.  None should buzz. 

 

If any of tests 3 or 4 show a connection, note which it is, and investigate.  First place to look is the circuit board carrying the decoder socket, and any wires coming into that board - it is not unknown to see poor quality assembly with a wire touching two connections when it should be on only one.  

 

 

Edited March 16, 2021 by Nigelcliffe

[pheaton]

19 hours ago, GoingUnderground said:

Albert Einstein is supposed to have said that insanity is doing the same thing over and over again but expecting the result to be different.

 

   On 15/03/2021 at 19:55,  Nigelcliffe said: 

Testing a loco which is known to be faulty, by putting in more decoders and hoping they work isn't sensible in my view.   

 

 

what you mean you have never dropped a loco screw on the floor...and then purposely dropped another to see if it lands in the same place??????

Edited March 17, 2021 by pheaton

[Butler]

Hi

Thank you Nigel. I have done that test and all is OK. Refitted the blank and it runs on DC fine

Although at first just feeding power to wheels it sounded rough. Then ran it on short piece of DC track, fine, and it was drawing 0.12 Amps flat out full 12v!

so all seems fine but scared of putting another chip in. 

Dont know now!

Thanks anyway 

B

 

[Geep7]

If it's running ok on DC, then I suspect that the decoder socket is possibly faulty. It has been known for some of the soldering across the back to be "untidy", and there may just be one blob that is slighly touching another, and therefore causing a short on DCC, but no issue on DC.

 

The Hornby 73 runs perfectly fine on DCC, one of mine is even fitted with a Legoman sound chip. As regards it vs. the Dapol 73, there are plenty of for and against arguements which I won't list here, you're best off checking out the Dapol 73 thread for that. Personally I think the Hornby (ex Lima) 73 is still a good model (I think the body shape still just about edges ahead of the Dapol one), just not a finely detailed (especially the underframe), but nothing that a bit of modelling can't fix.

[Butler]

Thanks, but as I said in my reply to Nigelcliffe, I have tested each pin of the decoder socket, no shorts. I removed it and looked underneath, doesn’t appear to be touching anywhere, But, it looks a little scratched as if someone had run a screwdriver along the gaps, it wasn’t new when I got it , maybe it has been a problem before, but there’s nothing to be seen wrong.

could it be , as I said before, the motor sounded rough at first, could a slightly seized motor blow a chip?  Maybe running dc has cleared it?

W

[Hamburger]

6 hours ago, Butler said:

 . . .could a slightly seized motor blow a chip?  Maybe running dc has cleared it?

This is what the Zimo manual says, should be the same for other decoders:

"Unfit or defective motors (e.g. shorted windings or commutator) are not always recognized by their high current consumption, because these are often just short current spikes. So, they can lead to decoder damage including damage to power amplifiers due to long-term exposure."

 

 

 

[roundhouse]

On 15/03/2021 at 16:56, Butler said:

Hi

Thanks for the reply, They were both Hattons 8 pin direct, I will take another look at it, i could put the blank back in and rig dc up. Will any 8 pin blank do? All got a bit mixed up in my boxes.

B

Running on DC doesnt always show up the issue. I have had few Hornby locos ( and some Farish N scale 6 pin fitted locos) that ran fine in both directions on DC with the blanking plug but when a decoder was inserted the decoder blew due to 'tin whiskers' as there was a solder / wire bridge across the underside of the 8 pin socket no doubt when the wires were soldered on in the factory, in one case the loco ran in one direction fine but then blew the decoder when ran in the other direction. Nowadays I tend to unscrew the socket and check the wiring to the socket.

 

As an aside, I have two Hornby Adams Radial tank locos where the pick up wiring to the socket was all over the place with some wired to the wrong pins. Worked fine on DC.

[Nigelcliffe]

If the loco passes the meter tests I listed earlier, then I'm out of ideas without inspecting the loco.   

 

There are theoretical failures, around parts moving, small whiskers of wires which can move, motor faults, etc..  But I've not handled one of these locos, so no idea if specific failures are more or less likely.  

 

If wanting to chance another decoder, then one of the European brands with known records on over-load protection working (eg. Lenz, Zimo) might be useful.  Lenz may be the better option because there are some CV's which will report the nature of faults.      But, even a decoder with over-load protection might hit a situation where the overload fails and it goes in smoke.  

 

 

- Nigel

[GoingUnderground]

I don't know the model, but in the past there have been problems on some models which have a live metal chassis that when the decoder plug was pushed fully home in the socket the plug's pins touched the chassis. If your 73 has a metal chassis that might be something to look at.

 

Also make sure that if the pins do project below the socket that they're not touching any uninsulated wires or stray blobs of solder from adjacent terminals on the socket. you won't spot these sorts of problems with a continuity tester as they'll only show up when the decoder plug is in place. And do NOT test for continuity with the decoder plugged in or you could damage the decoder just by testing with a multimeter.

[GoingUnderground]

22 hours ago, pheaton said:

what you mean you have never dropped a loco screw on the floor...and then purposely dropped another to see if it lands in the same place??????

Frequently, with the same result, I lost them both! 

Edited March 18, 2021 by GoingUnderground

[Butler]

Thanks for all your comments, if I had to guess, I’d say that the motor hadn’t run for a while, and  not tried on dc by me first (lesson to be learned there), It seemed a bit rough at first,now smooth. Probably overloaded the decoder. 

Might be ok now when I feel brave enough!

Anyway, I’m prefering the Dapol 73, despite mixed reviews on its running, it just looks good.

B

[Butler]

Bain of my life dropping tiny parts, fortunately the other half is brill at finding them. Except my Brittania loco, which lost its cranks going round the track, found all the parts except a tiny bush, off the rear drive wheel. Searched forever on the track. No! And there not available at present! Hey Ho!

B

 

[gordon s]

Not the same loco, but I had a similar experience recently where Nigel came to the rescue and pointed me in the right direction. Loco ran perfectly on DC, but dead short on DCC.

 

Whatever you do, always use the programming track as that in itself limits the possibility of blowing a decoder.

 

 

Edited March 18, 2021 by gordon s

[Yardman]

What usually toasts decoders is shorting a pick up wire (red 0r black) to a Motor wire (orange or grey). In a case like this the loco will sometimes work ok on DC but not DCC. I had a case where the loco would work fine with the body off but immediately killed a decoder when the body was clipped in place. It turned out the body was crushing a motor wire just enough to short through the insulation of a motor wire to the chassis. Close inspection and dismantling will usually reveal the problem. With the decoder plug out, use a meter to check between motor wires and pickups. It should read open circuit.