Lionel legacy GP7 won't move

Well, if the DCDS is drawing excessive current, I'd be looking at the wiring to/from the DCDS, and especially to the motors.  I'd also carefully check the motors and truck gears, you may be having a motor stall.  If you've replaced the DCDS, and the repair folks did also, that seems to indicate the root cause is not the DCDS, but rather something downstream.

Blackjack-this may be a long shot, but I had a similar issue with my Legacy GP-7. After careful examination, I found some of the rubber insulation located above the motor's flywheel in the cab area had deteriorated and the debris had "locked" the motor.

After carefully removing the failed insulation and making sure that it was not binding the motor or flywheel, the locomotive now runs perfectly.

Thank you both for the replies. I looked at the motors, and they don't appear to be physically jammed by anything, since they spin without significant resistance when I turn the flywheels. I also found another wire with some damaged insulation, although it is not near the motor driver board, so I'm not sure if it has anything to do with the issue.

Blackjack-does your locomotive run with the shell removed?

Last time I checked, it didn't.

I just replaced the motor driver board and the motor with the encoder board attached to it. Both motors are now responding to commands, but they move very sluggishly, as if they are struggling to turn. What could be causing this? The motors still don't seem to be jammed by anything. I'm worried to keep running the engine because I want to prevent any new damage. 

I'd find out why the motors are not turning freely first.

I did some more work on it, and I think the new motor is spinning the wrong way. I'm not sure why this is happening, because I thoroughly analyzed the wiring chart for this locomotive, and everything looked correct. I must have missed something. I'll keep looking for a mistake.

Well, if one is spinning the wrong way, that will CERTAINLY be a major issue and could cause a motor stall and kill the DCDS.  Of course, if you verify that to be the case, just swap the leads on the offending motor.  Since you replaced the motor and encoder, my guess is you just swapped those leads in the process.

@gunrunnerjohn posted:

Well, if one is spinning the wrong way, that will CERTAINLY be a major issue and could cause a motor stall and kill the DCDS.  Of course, if you verify that to be the case, just swap the leads on the offending motor.  Since you replaced the motor and encoder, my guess is you just swapped those leads in the process.

That partially solved the problem. I switched the leads on the encoder, and the engine is now running smoothly, but when I run it in reverse, it shorts out the transformer, and the DCDS gets really hot. I have no idea what could be causing that.

You have a short to ground somewhere it sounds like.  I've just fixed a couple with that issue, and I have another one coming in that sounds like the same problem.

Would that be caused by an exposed wire touching either the metal part of the DCDS heat sink or the chassis? I'm not exactly sure what to look for.

The DCDS driver FETs are live, and some of the installations have a heatsink that doesn't have insulation, so if anything gets in contact with that, it's a problem.  I believe the modular board GP7 is one such installation, they don't insulate the heatsink pieces, they just put them in a plastic carrier.  IMO, a stupid arrangement, but I wasn't in charge.

The FETs are definitely what failed on the original board. There's a metal part of the heat sink that is supposed to attach to them. Do you think it would be a problem if I just left that part out?

The heatsink is necessary if you plan on pulling anything with the engine. The heatsink on those is marginal already, leaving it out will not be a good idea.

I've replaced FET's on a number of these in the past, that's my first inclination for failure of this type.  If that doesn't work, then I get a new one.

Do you know what type of FETs I should use? I don't know why the FETs failed on the original board and are now failing on the new one. I'm worried that there could be some other issue that I'm not noticing.

The reason the FET's are failing is you have a problem that's not just the DCDS!  You need to track that down before you smoke more boards.

Look at the numbers on the DCDS, I don't have one handy to read them off.  As I recall, there are two types, two each N-Channel and P-Channel types.  I probably have them in my parts box.

I concede that GRJ is far more knowledgeable in this area than myself. Since these are DC motors, consider removing the wires from the motors or isolating them from the other components and run each motor on DC power. This is to verify that the motors and gears and wheels all turn smoothly, that nothing is binding. If they are binding excessively or hard to turn, they could be drawing more amps and potentially overheating components. You’ve come this far, one extra little step won’t take to long. Plus you get peace of mind that it’s not a motor/truck/gear issue. I keep a DC power pack handy for such occasions.

Steve

That sounds like a good idea, Steve.

Mark in Oregon

It's easy to test the motors, just unplug the 6-pin black plug from the DCDS, that isolates the motors.  Connect your DC supply to a motor and see if they run freely.  If you have a decent meter, measure the current draw of the motors running to see if when freewheeling it stays well below an amp, probably closer to half an amp.

Also, it's important to individually rotate the flywheels by hand through at least one full rev of the drive wheels and check for any binding or change in resistance of rotation.  They should rotate freely at all times.  If not, you need to address that.

I still think if the DCDS is getting hot that you have a wiring issue.

I'll try testing the current draw, but I also think that this is most likely a wiring issue because there isn't much resistance when I turn the flywheels by hand. 

You should be looking for any change in the resistance, they should turn very freely all the way around.

Next, unplug the motors from the DCDS and start looking around with the ohmmeter to see if anything is shorted to anything else.

I just tested the current draw of the motors, and they were only drawing about 0.35 amps, so they're likely not the issue. That only leaves a short circuit as the cause of the overheating DCDS. The problem is that I've looked at the wiring diagram for this engine and found no issues with any of the wires that have anything to do with the DCDS. There must be something else that I missed. I'll keep looking.

I've worked on a number, and I have one here, that has wires routed under the DCDS and they get pinched and short.  You need to actually trace the wires and make sure the wire routing isn't causing the issue.

@gunrunnerjohn posted:

I've worked on a number, and I have one here, that has wires routed under the DCDS and they get pinched and short.  You need to actually trace the wires and make sure the wire routing isn't causing the issue.

I wasn't able to find any pinched or exposed wires, but I did find a group of wires that appeared to be poorly soldered together and insulated with heat shrink tubing. I'm wondering if this could be some kind of manufacturing error which led to the failure of the original DCDS. 

Hard to say, usually an open wire won't kill things, it's a short somewhere that's bad news.

I looked at the wires that were all soldered together, and something doesn't add up. Two of the wires are connected to the truck grounds, another was connected to the "off" position for the odyssey switch, and another was connected to the AC regulator. The wiring diagram doesn't show any of the wires coming from the AC regulator to be connected directly to ground. That wire should go to the "smoke on" terminal. Furthermore, a different wire from the AC regulator is soldered to that terminal, but the diagram shows that this wire should be connected to the third rail pickup. I removed the smoke unit when I first disassembled this engine so that it would be out of the way, but I remember the smoke unit turning on immediately when track power was turned on. I'm pretty sure legacy diesels aren't supposed to do this. I don't know if this could be connected to the DCDS issue, but somebody definitely made a mistake when putting this thing together. I'll keep looking for other errors before I fix this wiring issue, just in case I missed something.  

Not sure what wiring diagram you're looking at, but there is indeed a real ground to the AC Regulator module.  AAMOF, there are actually two grounds provided, for reasons I don't fully understand, they're internally connected.

If someone has been in screwing around with the internal wiring, that's a red flag.  As for the smoke turning on immediately with power, that sounds like a shorted AC Regulator module.

https://www.lionelsupport.com/...s/7148728563256.jpeg

This is the chart I've been using. Terminal 2 on the AC regulator is shown being connected to the "Smoke on" terminal, but it is labeled "GND". The wire in terminal 3 is shown to be connected to the third rail pickup, but mine is soldered to the smoke unit switch. This diagram is for the pennsy 8512. My engine is pennsy 8510, but I would assume that the wiring for these engines are identical. I'm sure that this is the correct diagram.

No problem there, they're interrupting the power to the smoke unit.  The other ground goes only to the smoke unit, so that's just a somewhat odd way of switching them.  The pinouts on that regulator are correct, I'm holding one in my hand.

That diagram looks correct to me, if the engine is wired differently, not sure what to say.  You'd need to actually draw what you have for us to analyze what is going on.

I made this video where I show the difference between the diagram and the actual locomotive. I apologize for the bad camera work. I also incorrectly referred to the ac regulator as a "voltage regulator", and the broken purple wire that is shown at one point is supposed to be connected to the run/program switch, so it's unrelated to what I was trying to show. Hopefully this video is able to clearly illustrate the problem.

I think you'll find if you analyze it, swapping the ground and hot wire didn't change anything logically.  I'm sure you'll find that on the other side of the smoke switch is actual track power (center roller).  Truthfully, I was a bit surprised to see them switching ground to the voltage regulator, it's more common to switch the track power lead as you are seeing.

I can't imagine this is having anything to do with the running issues.

I can hardly follow this sophisticated and well articulated dialogue, but I very much enjoy reading it, and hope that some of the expertise expressed will seep into my brain.

Does it sometimes happen that a particular locomotive is simply a lemon, which happens with motor vehicles?

I guess those with great mechanical knowledge like you folks may find it intriguing to figure out just what makes the engine a lemon and how to turn it into lemonade metaphorically speaking. 

I'm convinced I have a newly acquired MTH Proto 2 engine (the subject of another thread) that is a lemon and will probably ultimately hire an expert and upgrade it to Proto 3. Arnold

@Arnold D. Cribari posted:

I can hardly follow this sophisticated and well articulated dialogue, but I very much enjoy reading it, and hope that some of the expertise expressed will seep into my brain.

Does it sometimes happen that a particular locomotive is simply a lemon, which happens with motor vehicles?

I guess those with great mechanical knowledge like you folks may find it intriguing to figure out just what makes the engine a lemon and how to turn it into lemonade metaphorically speaking. 

I'm convinced I have a newly acquired MTH Proto 2 engine (the subject of another thread) that is a lemon and will probably ultimately hire an expert and upgrade it to Proto 3. Arnold

Yes, I think that this engine is just a lemon, as this seems to be the result of some kind of manufacturing error. 

I haven't been able to make much progress on it, but I partially reassembled it today to see if the issue was just a faulty heat sink, but I found that the sounds don't work anymore. The speaker just makes a loud humming sound, but the engine still moves. Did I fry the sound board somehow? I don't think I can get a replacement from lionel's web site, so I realy hope that that's not the case. 

I think it's time for a repair person to look at it, it seems like it's going downhill.

@gunrunnerjohn posted:

I think it's time for a repair person to look at it, it seems like it's going downhill.

I think that the sound problem was caused by part of the speaker contacting the frame. I put some electrical tape on it, and the sounds work fine now, so that was just a false alarm.

But I agree, I think my only option now is to bring it to a repair person, since I still haven't been able to find any messed up wires. I've heard that thermal paste can be used to mitigate the heat that these motor driver boards generate, but I don't know how effective that will be in my case.

If it's not moving and the DCDS is getting hot in reverse, no amount of heatsink compound is going to fix it!  Most likely you have a short somewhere, and the FET's are trying to overcome it.  They'll cook soon.  This is usually caused by something under the DCDS, the heatsinks are not insulated.

I brought the engine to a repair place a few weeks ago and just got it back today. They weren't able to fix it. I'll keep looking at it, but I don't know what else I can do.

I may have spoken too soon. I just ran the engine for about 2 minutes with my hand on the DCDS heat sink and barely noticed any temperature change. Before I brought this engine in for repairs, the heat sink would get so hot after only about 30 seconds that I physically could not touch it. It's also not shorting my lionel CW-80 anymore. I'll run it for a little bit longer before I reassemble it just to make sure it won't break down again.