X9242 motor issues

[Deltic Man]

Evening Gents. I have a R2350 class 50, and not being able to source a replacement board, I took the decision to remove it and hard wire a decoder via a fly lead. The issue I had was that the original motor (X9242) had continuity across the terminals and therefore would produce a short. I purchased a new motor and wired it temporarily to a decoder ( out of the chassis). All seemed good, then all of a sudden, a short issue, and continuity through the new motor. Can anybody explain or better still advise how to get over this issue as I really want to run this beautiful loco.

[96RAF]

There has to be continuity through a motor or current would not pass through the armature coils to create motove force via the magnets. The commutator makes and breaks this continuity as the armature rotates. Check the meter as you rotate the motor shaft.

[Deltic Man]

Ok, just tested both motors and I have continuity right through a revolution of the motor. What other reason can there be for a shorting issue. I’ve discounted track, pick ups and chassis as I’ve tested this motor with a gaugemaster decoder out of the chassis

[2e0dtoeric]

Have you forgotten to fit the insulated bush that goes on one end of the brushes spring?

[walkingthedog]

Think it’s a sealed unit Eric, no brush spring.

[jane1707819582]

connect the motor directly to a 9v battery , does it still short out ?.

[96RAF]

This where a decoder test rig would be handy as you could mount the decoder or a blanking plate and slave in this motor in lieu of the rig motor. That rules out any loco induced problems hence narrowing down the possibilities of what is causing this short.

[morairamike]

Here is a way to check if the motor had an internal short.

http://gracomfg.blogspot.com/2013/01/tech-tip-how-do-i-check-dc-motor-for.html?m=1

[Deltic Man]

RAF69, i‘ve already done that, so that I could discount track, chassis etc. The only thing left is the decoder itself(which I don’t want because it could become expensive!) but I can’t understand why it should blow decoders. It just seems strange that the impromptu test rig ran for a bit then shorted. By the way, the motor runs fine on a 9v battery

[jane1707819582]

RAF69, i‘ve already done that, so that I could discount track, chassis etc. The only thing left is the decoder itself(which I don’t want because it could become expensive!) but I can’t understand why it should blow decoders. It just seems strange that the impromptu test rig ran for a bit then shorted. By the way, the motor runs fine on a 9v battery

do you have any means of testing the motor current ?

[96RAF]

I think the motor if playing up on a test rig must have an internal intermittent short which when running on a battery is ignored by the brute force current from the battery but when in circuit with less robust components it manifests as an identifiable short.

 

Sensitive monitoring kit as suggested could give some idea of what and when.

[Deltic Man]

What sensitive monitoring kit, I have a electrical tester ?

it just seems strange that a brand new motor suddenly develops this issue, ok I know dcc runs at around 18vac, taking Into consideration Hornby replaced the original board and everything was then ok, I find it hard to believe that 18v would be too much for this can motor to handle. It just seems really weird and I’m almost pulling my hair out with it

[jane1707819582]

What sensitive monitoring kit, I have a electrical tester ?

it just seems strange that a brand new motor suddenly develops this issue, ok I know dcc runs at around 18vac, taking Into consideration Hornby replaced the original board and everything was then ok, I find it hard to believe that 18v would be too much for this can motor to handle. It just seems really weird and I’m almost pulling my hair out with it

if your electrical tester can be set up to measure current, this will indicate any motor short , (which from what you are describing may not be the problem ), set it up with a dc controller connect the ammeter in series with the motor ,read the current , turn up the voltage the current will move with it , then stall briefly the motor the current will increase ,if the current should increase whilst the motor is running normally this will indicate an internal short . eliminating the two motors you have .

 

 

[96RAF]

Doing a DC stall check will not monitor what is happening at the motor under DCC control. For that you either need a RRAMP meter or a ‘scope, both are sensitive and heavy on the pocket.

 

Be aware you need to have a meter that has a 10A DC current range, not all have, many being 200mA limited.

 

Putting 18v through a nominal 12v motor can’t be good for it (+50%). Noting that Hornby controlled DCC is around 15v pseudo AC and the motor never sees this as the decoder rectifies it and provides PWM DC At up to 12v.

[Chrissaf]

As Rob, says DCC is not 18 volts AC in the traditional sense. For one thing nearly all normal current meters are calibrated to read AC voltages as a Sine wave. DCC is technically a 'Bi-polar' square wave of 28 volts 'peak to peak'. Thus a normal AC voltmeter will interpret this as about 14 to 15 volts AC. This is why Rob included the term 'pseudo' in his text.

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The other issue is frequency. Most meters are calibrated to read 50/60 Hz frequency. DCC is a variable frequency because of the DCC signal variable 'Mark / Space' ratio. But nominally is about 7,100 Hz.

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To measure DCC voltages and current accurately you need as Rob says a RRAMP meter, these retail around £100.

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However, if one has the necessary skills, you can build an IC based DCC Ammeter for a mere few pounds. This web page gives all the constructional details.

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http://www.circuitous.ca/DCCammeter10.html

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Note this electronics project only measures DCC current, not voltage. If you want to measure both (accurately) you need the RRAMP meter.

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I am only making this post for general information of those who are interested in the technology and those who might want to make a cheap DCC current meter. I am not suggesting that the OP needs to make this meter to resolve his motor issue.

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[Deltic Man]

Thank you gents, this all getting a little technical. I’m using a gaugemaster prodigy control system and when I put my volt meter across the track I get 18vac. All my other DCC locos work fine ( TTS 31/40/47 and a CD motored HST) It just seems to be this motor and or Decoder, now, having two X9242 motors doing the same thing and reading your posts, I’m inclined to think that it maybe the gaugemaster decoder that is at fault. Having said that, I don’t really want to spend a fortune on different decoders just to prove a point,as I was looking in the future to putting the Hornby Class 50 sound decoder in it. Do I need to put resistors/Diodes  in the circuit between Decoder and Motor to decrease the voltage ???? I really don’t know...... do I look to put a different can motor in the loco.......?? I’m open to options

[walkingthedog]

Have you got a decoder in another loco you can put in the CL50 to see if it works. It doesn’t matter what voltage you get across the track, the decoder send 12 volts DC to the motor. 

[Chrissaf]

Do I need to put resistors/Diodes  in the circuit between Decoder and Motor to decrease the voltage ????

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Absolutely not.....any modification in this circuit area will only make matters worse. Apart from which, as WTD above says. A decoder that is not faulty converts whatever it finds on the track side of the decoder to something that is correct for the motor.

[Chrissaf]

Read both pages of this previous thread. It has some useful advice. I acknowledge that the OP has stated he has already removed completely the known bad PCB. But maybe fitting this alternative PCB board will solve the issue.

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https://www.hornby.com/us-en/forum/post/view/topic_id/20277/?p=1

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[jane1707819582]

Thank you gents, this all getting a little technical. I’m using a gaugemaster prodigy control system and when I put my volt meter across the track I get 18vac. All my other DCC locos work fine ( TTS 31/40/47 and a CD motored HST) It just seems to be this motor and or Decoder, now, having two X9242 motors doing the same thing and reading your posts, I’m inclined to think that it maybe the gaugemaster decoder that is at fault. Having said that, I don’t really want to spend a fortune on different decoders just to prove a point,as I was looking in the future to putting the Hornby Class 50 sound decoder in it. Do I need to put resistors/Diodes  in the circuit between Decoder and Motor to decrease the voltage ???? I really don’t know...... do I look to put a different can motor in the loco.......?? I’m open to options

which model of decoder are you using ?

[Deltic Man]

Can’t get a version 1 X9788, only the newer version with the white molex connectors on the ends, I’ve already been down that route which was why I took the decision to hard wire a decoder via a fly lead.

jane2, I was using a Gaugemaster DCC26, but I’ve just ordered a handfull of R8249 decoders

[Chrissaf]

The fact that you state you have removed the original Class 50 PCB got me thinking. These PCBs are packed with electronics and serve a purpose. One of them being how to make what are in effect DCC controlled Directional Lighting work in a DCC Ready model without the decoder. The PCB circuit may also provide 'constant current' regulator circuits for the lighting LEDs.

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Now if your DCC mod removed the PCB but also included wiring the decoder function outputs up to the front and rear LEDs, then if you didn't replace the PCB with current limiting resistors into the LED feeds. The lighting circuits can effectively become a 'short circuit' across the decoder function power. Some decoders might just blow like a fuse, but some also shut down to protect themselves.

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One way to test for this theory would be to unsolder wherever you have terminated the decoder 'Blue' wire as part of your mod (assuming you have terminated it somewhere). With the 'Blue' wire disconnected. Does the fault go away. If it does and you hadn't included any current limiting resistors in the white / yellow wires, then you need to replace the function of the removed PCB with some resistors (probably a value between 680 Ohms and 2200 Ohms is needed). One resistor in each USED function wire (except the Blue). The resistors can be standard 5% tolerance 1/4 Watt. The actual values need to be subject to experimentation if LED light brightness is affected. One also needs to understand the exact connectivity of the LEDs at each end of the loco to confirm the physical location of the resistors in the overall circuit.

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If you are ONLY using the red, black, orange and grey wires on the decoder then ignore this reply (above).

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EDIT:

.....with the white molex connectors on the ends,

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They are not Molex connectors they are JST ZH connectors and readily available from on-line electronic component suppliers so that you could terminate your loco wires on JST ZH 8 way plugs and use the white connector PCB.

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The details are covered in my previous post on this link below:

https://www.hornby.com/uk-en/forum/class-50-main-pcb/?p=1

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[Chrissaf]

Update.

The component links contained in my linked post in my reply above have expired. Here are new links to for the same product but using a different component supplier.

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JST ZH Data Sheet

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JST ZH Pins 100 Pack

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JST ZH 8 way Plug Housing. (minimum order value = 5)

[Deltic Man]

Chrissaf, I had only connected red,black,orange & grey, so as you said ignore.

i think I have a later X9788 that I ordered from AC Models. Do you or anyone have a wiring diagram for the pin positions ??

[Deltic Man]

Chrissaf, UPDATE.... found my X9788. Now looking at the underneath of the board, I take it RT is Right Track, LT is Left Track, M+ is Motor Positive and M- is Motor Negative. Assuming this is correct, the fly wires I have out of the plus are : 3,5 & 6 which I assume are blue, yellow and white on a decoder. Do you know what I need to connect to what on the lighting boards of the class 50 (X9252)