Coupler problem..Yeehaa, no problem

I don't have his book

That's your first problem, however, it's easily an d inexpensively resolved.

There are only a few things that can cause a coupler to not fire:

• One or both wires have become unsoldered from the actual coupler itself. This is quite common as the cause of this kind of failure.
• The circuit between the coupler and the PS2 board has become broken. This may be because the inline connector is loose or disconnected, or a wire is broken, perhaps inside of its insulation.
• The FET on the PS2 board that operates the coupler has failed.

The odds are good that it's one of the above.

When I posted a similar problem on the TMCC  thread, the answers came back-- raise

the voltage. I prefer running at 16 volts rather than 18-20 volts so I quit worrying

about the couplers.

Al W.

raise the voltage

That's the wrong answer for a PS2/PS3 engine running under DCS.

Al W., I'm curious; what makes you choose 16 volts? I run bricks so I'm at 19 volts which is the unadjustable output. I'm thinking maybe to extend incandescent bulb life or to make the bulbs not as bright.

I am adding a new section I will control with a PW ZW so I will be able to control voltage there.

Barry:

Note  that I said that " raise the voltage"  was a response on the TMCC thread.  What voltage do you recommend for DCS?

Jeff:

I run both TMCC and DCS. I have no problems with 16 volts except that some

 TMCC couplers fail to open.

16 volts works well for me. Considering transformer voltage  regulation, when the

load lightens the voltage does not soar to greater than 18 volts if I set it

originally at 16 volts.

Al W. 

You really can't measure the voltage when fired, this is a timed pulse.  You can measure that you have continuity thru the coupler coil, you can connect a good coupler and see if it fires, you can inspect the FET on the PS-2 3V board.  If this is a PS-2 5V board you are out of luck as the FET is not reachable.  G

Thank you for the reply, appreciated. So...............

You really can't measure the voltage when fired, this is a timed pulse.

That probably means I can't input to the coupler a voltage (ac or dc) that would get it to fire then, correct?

You can measure that you have continuity thru the coupler coil

That was one of my next steps. I assume that one end of one of the wires from the coupler going inside must be unsoldered so it does not affect the reading, correct?

you can inspect the FET on the PS-2 3V board

Again.....might be above my pay grade. I am not sure what a fet looks like (I bet not like my pet!) and when I find it (I am sure I can find a photo or someone can post one) I am not certain then that "inspecting" it visually would do me any good, since I am not certain what a bad one vs. a good one looks like. Maybe you can help me with that, but let me run the continuity test and also that other good idea you had, try a known good coupler hooked to the wires that exist to the none working one. Good reply.

Last thing...on the diesel, does each coupler have its own FET or does one do both? Because if the latter, then the FET is good since my front one works. If the former, then yes, a FET might be bad.

Barry, feel free to chime in. I just put in a plug for your book!!

Thanks, Greg (anyone else get spell check to highlight " coupler ?"

If you take the shell off and unplug the coupler you can apply DC voltage quickly from a 6-9V battery to see if it fires.

Yes individual FETs for PS-2 3V.  Single FET supposedly for 5V boards.  G

Greg,

Try tapping the end of the coupler with your finger when trying to uncouple a few times. Sometimes they just get stuck from lack of use and once moved, will work fine. A drop of oil helps also.

Al,

Note  that I said that " raise the voltage"  was a response on the TMCC thread.  What voltage do you recommend for DCS?

If you're not interested in running multiple trains on the same TIU channel at very high speeds, 16 volts should work fine.

GGG,

If this is a PS-2 5V board you are out of luck as the FET is not reachable

On the contrary, the FETS are easily accessible, right on top of the board. Often, it's not even necessary to remove the board itself. I've changed a few FETs on 5 volt boards.

Single FET supposedly for 5V boards

Nope, 2 FETs, one per coupler, on the 5 volt boards.

Barry, As an accomplished author/expert you need to do better research before you answer.  I do.  Please tell me where the Coupler FETs are on a PS-2 5V board?  If you check your ASC notes you will find they are not shown or listed as replaceable.

If you look, at the PS-2 3V diagram you will find they are not on the bottom of the board they are on the top of the processor board in a separate location side by side.

As I stated I was told it is a single transistor that controls both for a PS-2 5V board. MTH told me when I was researching a repair for a PS-2 5V with one coupler that would not work.  Either way it was not a replaceable part without cutting the board in half.

While I have a few 5V boards I have cut in half, I haven't devoted any time to tracing the interior chips yet.  G

Menu/Advanced/ Reset engine/ Feature reset.... When things go a muck, this one usually fixes it unless there's some serious hardware issue.

GGG,

Please tell me where the Coupler FETs are on a PS-2 5V board?

FETs...

It is hard to believe you can't admit when you are wrong.  I asked you to show me which one is the "coupler" FET.  It ain't there....:-(  G

 Here is the PS-2 5V coupler Transistor (Not FET).  It sits behind the audio chip on top of the processor board.   The top power section is removed along with other components.  You can clearly see the traces from pin 8/9 of the 12 pin going to legs 5/6 and 7/8 of the transistor. 

GGG,

It is hard to believe you can't admit when you are wrong.

OK, I was, indeed, mistaken. I incorrectly recalled that the coupler wasn't among the FETs that were easily accessible. It would appear to be the exception to the rule.

 I asked you to show me which one is the "coupler" FET.  It ain't there....

I figured that, if it was there, you'd identify it. If not, you'd correct me. Which you did. I appreciate the "lesson".

Thanks - really!

Barry, Thank you, and you are welcome.

So Gregg did you get to do any testing?  G

Nope not me, although I did about 15 upgrades when  the kits first cane out,

You want greg, don't you?

Never a dull moment with you and Barry .  You're both right. That 8-pin package (labeled 7103) contains two separate FETs - one for the rear coupler, the other for the front.  So you're right in that it's a single part that does both couplers and Barry's right in that there are two independent FETs.  BTW, a FET is a transistor (FET=Field Effect Transistor).

cngw: I suggest you pull the connector at the circuit board and measure the resistance of the coupler using a digital meter at the low-ohms setting.  It should be a few ohms but not below, say, 1 ohm.  If you're going to try to fire the coupler with a battery to test it, note that that battery needs to have some serious juice behind it.  A 9V transistor radio battery is not going to supply the Amps of current to drive a few ohms!  If in measuring the coupler resistance you discover it is shorted (below 1 ohm or so), then don't try to test it with the other coupler's drive circuit.  That is, if there's a short in the coupler itself or in the wiring to the coupler, that could be the reason its FET blew up.  So you wouldn't want to blow the working FET by trying to drive a problem coupler.  If you want to see if the rear coupler FET is working, then try driving the front-coupler by re-arranging the wires to the connector.

Yes, it is possible that just 1 of the 2 FETs is damaged. And while in some cases you can "see" a damaged FET by visual inspection (e.g., a pock mark or hole in the package), it might look cosmetically intact.  If you conclude the dual-FET part is bad, as the guys point out replacing that part is a bitc* but it has been done.  The dual-FET part itself is available from DigiKey for $1. 

Hmm, I might have missed it but did you tell us if this is a PS-2 3V board or a PS-2 5V board? 

I have never had a coupler fail to fire due to low voltage.  Whatever you do, do not let one of the coupler terminals touch ground. Before applying any power to coupler directly, unplug it from the board

Have you tried switch the coupler plugs between fron & rear, which would pin down whether coupler or board.

No idea on that one, but when I pull the shell, I will know since the battery seems to be bad anyway....won't hold charge.

Nope not me, although I did about 15 upgrades when  the kits first cane out,

You want greg, don't you? 

YES HE DOES!! Greg

Have you tried switch the coupler plugs between front & rear, which would pin down whether coupler or board.

See above....no time yet. May not do a switch anyway, or if I do, I may move the front working one to the rear.

cngw: I suggest you pull the connector at the circuit board and measure the resistance of the coupler using a digital meter at the low-ohms setting. 

That sounds like a plan.

Thanks to everyone for the interest! I will keep you posted. Greg

(Not Gregg. People ask me when I tell them my name for them to write down, "Do you spell it with one g or two?" I tell them two....if I only used one, it would be pronounced Gre.  Get it??!!! They meant 2 g's or 3 g's ! So, Gregg, you can tell them you spell it with 3.) 

As mentioned earlier the coupler signal output from the electronics is a short timed pulse - and perhaps difficult to register without an oscilloscope or whatever.  This short video shows an incandescent holiday light bulb (2-3 Volts) attached to the two PS2 coupler output wires in place of the coupler.  With 16V on the track here's one way to see if the electronics is generating a pulse. The video has sound.

The easiest thing to try is a feature reset and tap the coupler as Joe suggested.  Maybe you've  already  tried the reset? I don't know. Gregg... 3 Gs

Menu/advanced/ Reset engine/ feature reset....

cngw, don't worry I haven't abandoned the sinking ship (yet)...

For the record, since your battery is the 9V style, you have a PS2-5V board.

I still suggest you first pull the 12-pin connector from the main PC board set.  The video has 4 segments.  The first segment shows how to wiggle the 12-pin connector from the board.  The goal is to confirm the continuity-integrity from main board all the way to the coupler.  In the picture below I inserted some small pieces of wire in pins 2 (purple) and 8 (brown) so that I could easily measure the resistance with a meter.  These 2 connector contacts are the 2 wires that go to the rear coupler.  You should read the same 2.8 ohm resistance as your coupler confirming you have continuity through the harness and any intermediate connectors.  At the same time, if you didn't do it earlier, you should confirm there is no contact between the coupler wires and the chassis-frame (or at least something very high - in the Meg-ohms)

As for WTF?  Here's a closeup of the so-called 7103 chip which contains the 2 coupler FETs.  If the surface of the chip is bulging, or has some funny deformation or pock-mark (a close-up photo would be nice), it might be bad.  But these usually fail without any visible indication.

Here's the chip further back in case you're trying to locate it.

The 2nd video segment shows the 2-pin coupler connector.  It should wiggle right off and snaps right back in.

For now, ignore the 3rd video segment which shows how to remove a crimped wire from the 12-pin housing. 

You got my curiosity about firing a coupler AND a bulb.  I'd turn the track voltage down to 14V or less as putting both loads on the FET makes it work harder.  But I could fire both devices as shown in the 4th video segment; I had the engine on its side with some alligator clip leads attached to the roller and chassis.

One other thing to look for.  If you look closely at the lights, perhaps maybe more so at lower track voltage (say, 14V) when you fire the coupler, the lights flicker ever so slightly.  So fire your working front-coupler and watch the lights.  Then fire the back-coupler.  If you have continuity from main board to the rear-coupler (you confirmed the 2.8 ohm resistance), the lights should flicker in the same way.  That is, I suppose there is a microscopic chance that something is mechanically jammed in the coupler so it still draws the electrical load but does no mechanical work.

Well there you have it.  You have a broken connection from pin 2 at the 12-pin connector at the PC board and the black 2-pin coupler connector.  That is, pin 8 is making it back to the 2-pin coupler connector but for some reason pin 2 is not. 

I am not familiar with your engine, so do you have a small circuit board near the rear lights as shown in the video where I pull the 2-pin connector with the needle-nose?  If so, pin-2 from the 12-pin feeds not just the coupler but all the lights plugged into that board.  If your rear-lights are working then pin-2 is making it to that small circuit board and somehow it is not making it to the coupler connector.

Let me know if this makes any sense and if you need more discussion.  This is REALLY good news!  If it "just" a broken connection in the harness or in the coupler connector, then I think you'll be able to fix it...and much more easily than a broken FET.

I'm pretty certain we have the same small board just oriented differently.  Here is a backside shot of mine.  The board is labeled 1017-10 as shown in photo not that you can see this unless you take yours off. I think it will come right off by removing that black Phillips screw in the center of the board.

On the top side your board the row of holes is labeled 1 and 6 in white on the edge.  The purple wire goes to hole #1.  I'm sure you'll see the remains of the broken wire in the hole where the purple wire broke off.

For whatever reason it looks like you have two (?) brown wires coming into the small board?  I don't know what that wire is on the far right but you should be able to confirm the middle brown wire comes from pin-8 and goes to one of the black coupler contacts as shown by the yellow lines.

I guess to be precise, yes, pin-2 and pin-8 go to the 2-pin black coupler connector.  But in this case the 2 wires go through this small circuit board and pin-2 is shared with other circuits (the lights).  I think you're rounding 3rd base...

Wow, I don't even remember hitting the ball!

Thanks for all the help, I will post again after I dissect the board and repair the wire.

Greg

And an inside-the-park one at that.  Those are always the most exciting.  Well done!