Hot and common: where on PCB?

Keith L: Can't tell. Can you post a picture of the underside? That might help.

Here's the underside of the board:

See the GND/3RD on the connector?  GND is the wheels and 3RD is the center roller.  The two M- & M+ are the motor connections.

It also has connections for directional lighting and the smoke unit.  I believe the SW1/SW1 is the direction lock switch.

BTW, there should be an aluminum heatsink down the middle of the board bolted to all those TO-220 transistors, they'll cook quickly with no heatsink.

Thank you, John.

I do have the heat sink; it doubles as the mounting bracket for the board.

Now I have it all together, but I'm left with one item: a 470uF 35 volt capacitor. The defective board that I'm replacing had the leads of this capacitor soldered right in between the two flat black chips on each side of the board. (Frankly, it doesn't appear that anything is actually intended to be soldered at these locations.)

Should I solder the capacitor to the new board in the same places? Or, is there a better place to put the capacitor? Or, should I just omit it?

Well, the one I have which was removed from a working locomotive for a command upgrade has no external cap, so I don't know what that was for.

gunrunnerjohn posted:

Well, the one I have which was removed from a working locomotive for a command upgrade has no external cap, so I don't know what that was for.

With the new board, the engine (a K-Line conventional GG1) behaves the same way it did with the old board. The first time you apply track power, the engine sits, dead, for three seconds, then the lights illuminate and the engine moves, but in reverse. Thereafter, the engine operates normally (until it sits for a while without track power).

The board I replaced was not OEM. The engine was repaired 10 years ago, and, with no K-Line replacement board available, the Lionel board was installed. Is it possible that the repairer added the external cap because the Lionel board was not fully compatible and the cap was needed for normal startup?

If so, could it be that the cap became exhausted over time, and a new cap is needed? If so, is there another place I can locate the cap leads that would be more convenient?

If the locomotive starts in reverse, just swap the motor leads.

gunrunnerjohn posted:

If the locomotive starts in reverse, just swap the motor leads.

Yes, I could do that. Also, since it's a GG1, I could just turn it around. However, I'd still have that odd three second delay after track power is applied when the engine does nothing and even the lights don't illuminate.

The fact is, since someone put in the first Lionel board and a cap 10 years ago, the engine has worked normally--until recently, when it started this weird behavior of a three second lag and then moving in reverse.

I've replaced the board and there's been no change. I have not replaced the capacitor. What else is there???

Could it be that the motors require more voltage to start--this engine is die cast, is very heavy, and the gearing is very tight--than the non-OEM board is designed to pass through immediately? Perhaps this results in small pulses of current that are not enough to get the motors going, but that are enough to cycle the "reverse unit" twice, once to neutral and once to reverse during the three second lag before the current is sufficient to get the motors going and to illuminate the incandescent lights?

I tried to make a pair of locos MU with that type of reverse unit some years back. One reverse unit per loco. The problem was that the boards would not reset properly to the same state. Sometimes the loco would start in forward, sometimes in neutral before forward, sometimes in reverse. There was no way that two locos would predictably start up the same way. Those boards are in a parts box somewhere now. It was a waste of time.

First off - I don't know anything about your PC board.

I assume the PC board internally uses DC, and thus would have a half or full wave rectifier to create the DC from the track's AC. It would appear to me that there is a cap in the AC to DC conversion/regulation process that is taking a long time to charge, charge to a voltage level which is an operable DC level for the PC's electronics. So what may have changed? To change how long a cap takes charge, you control the energy being supplied to the cap by either changing the resistance between energy source, or how strong the energy source is.

Without a schematic, I would try to reverse engineer the PC a bit to see where the half or full wave rectifier is, then try to make sure all the diodes in the bridge are working. I would try to determine if there is a resistor between the bridge output and the cap, and make sure the resistor is within value. I would try to make sure that the center rail pick up to bridge, and bridge to engine frame-to wheels-to outside rail, are near zero ohm paths.

Wish I could be of more help!!

I'd have to know at least exactly where the extra cap was connected since mine didn't have one.  FWIW, I've never seen the board that I have do anything but start and run normally.  It worked fine until it was removed for a command upgrade.

The red dots show where the extra cap (470uF 35 volt) was connected by the repairer who replaced a blown K-Line board with the Lionel board 10 years ago. The Lionel board I just put in is exactly the same board, and, without the capacitor that was added, it behaves exactly the same odd way in this locomotive. At this point, I'm assuming that the cap stopped working. I've ordered a new cap, so I guess we'll see. But what's going on...

Well, that's right across the full-wave bridge that powers the board, so it's just a filter cap.  Interesting that the original board doesn't have that cap.  I'd stick it on and see if it helps.

FWIW, I just connected the one I have to a transformer and a motor.  It starts up in less than a second and reverses properly through the standard F-N-R-N sequence.  It has no added capacitor.

When I receive the replacement capacitor, I'll report on the outcome.

Here's the one I have, just plugged in the one plug with the power and motors and it worked 100%.

OK, I'm admitting defeat.

Here's a recap:

1. K-Line conventional GG1 new in 2001. Runs fine.

2. In 2010, board fails. Repairer replaces with Lionel board and adds external cap. Runs fine.

3. In 2019, locomotive begins an odd behavior at initial startup: instead of immediately going forward, it remains totally dead for 3 seconds, then goes backward.

4. In January 2020, I replaced the Lionel board with a new Lionel board that is exactly the same. I did not reconnect the cap. No change to odd behavior at initial startup.

5. I got a new cap with exactly the same specs and reconnected it in exactly the same way. No change to odd behavior at initial startup.

6. I like to know how things work and, if they do not work, why. But what else is there in this locomotive: the 2 motors?

7. I turn the GG1 around so at least it goes forward initially, and I accept the initial 3 second dead period.

Thank you, gentlemen, for trying to help.

The number of motors makes no difference to this board, one or a dozen.  I'm totally confused why your boards do something odd.

Long winded, but this is the next step I would take in trying to trace down this problem.

I would check the path from track to PCB. Since multiple boards act the same way, this would appear to me to be the next logical area to verify.

I would remove the body so I could access the PCB. I would put the engine on a piece(s) of track that are completely isolated, like a couple pieces of track on a workbench. @gunrunnerjohn identified to you the full wave bridge that the cap you replaced spans. At one end of the cap, the components immediately to the left and right are diodes, whose inputs come from the track. I edited your picture, identifying two of the diodes, and two measurement points that are the ends of the diodes, which I labeled Point A and Point B.

I would us an ohmmeter and put one lead on the Outside Rail (OR) of the track, then measure resistance to the Point A end of one of the diodes and write it down, then from OR to the end of the other diode Point B and write this measurement down.

Now move the ohmmeter lead from the Outside Rail (OR)  to the Center Rail (CT). Measure and write down the ohm reading from CT to Point A, and from CT to Point B.

You should end up with two zero ohm readings ( when I write zero ohms, I mean zero ohms or very near zero ohms, like below 10ohms) one zero ohm reading should be to Point A, and the other zero ohm reading should be to Point B, falling into one of the two situations below:

1) OR to Point A and CT to Point B zero ohms

2) CT to Point A and OR to Point B zero ohms

An incorrect situation would be, for example, OR to Point A is zero ohms, but CT to Point B is 200 ohms. Since OR to Point A is zero ohms, CT to Point B must also be zero ohms, and if it isn't, need to find out why not zero (dirty wheels, dirty pick up rollers, wire connection, etc.).

gunrunnerjohn posted:

The number of motors makes no difference to this board, one or a dozen.  I'm totally confused why your boards do something odd.

I wasn't referring to 2 motors vs. 1 motor. I was just trying to say that there's only the board, an external cap, and the motors. Both the board and the cap are new. It seems highly unlikely, but could an issue have possibly developed with a motor that could cause the weird behavior?

MED posted:

Long winded, but this is the next step I would take in trying to trace down this problem.

I would check the path from track to PCB. Since multiple boards act the same way, this would appear to me to be the next logical area to verify.

I would remove the body so I could access the PCB. I would put the engine on a piece(s) of track that are completely isolated, like a couple pieces of track on a workbench. @gunrunnerjohn identified to you the full wave bridge that the cap you replaced spans. At one end of the cap, the components immediately to the left and right are diodes, whose inputs come from the track. I edited your picture, identifying two of the diodes, and two measurement points that are the ends of the diodes, which I labeled Point A and Point B.

 

 

I would us an ohmmeter and put one lead on the Outside Rail (OR) of the track, then measure resistance to the Point A end of one of the diodes and write it down, then from OR to the end of the other diode Point B and write this measurement down.

Now move the ohmmeter lead from the Outside Rail (OR)  to the Center Rail (CT). Measure and write down the ohm reading from CT to Point A, and from CT to Point B.

You should end up with two zero ohm readings ( when I write zero ohms, I mean zero ohms or very near zero ohms, like below 10ohms) one zero ohm reading should be to Point A, and the other zero ohm reading should be to Point B, falling into one of the two situations below:

1) OR to Point A and CT to Point B zero ohms

2) CT to Point A and OR to Point B zero ohms

An incorrect situation would be, for example, OR to Point A is zero ohms, but CT to Point B is 200 ohms. Since OR to Point A is zero ohms, CT to Point B must also be zero ohms, and if it isn't, need to find out why not zero (dirty wheels, dirty pick up rollers, wire connection, etc.).

Thank you so much for the detailed instructions on how to diagnose further. I'll check it out.

Keith L posted:

gunrunnerjohn posted:

The number of motors makes no difference to this board, one or a dozen.  I'm totally confused why your boards do something odd.

I wasn't referring to 2 motors vs. 1 motor. I was just trying to say that there's only the board, an external cap, and the motors. Both the board and the cap are new. It seems highly unlikely, but could an issue have possibly developed with a motor that could cause the weird behavior?

OK, I'd have to be at least looking at the wiring and motors since you've replaced the board.  Of course, with four wires, you can fire up either of the boards you have on the bench with a spare motor and see if they exhibit the behavior you describe.

I am just trying to follow a progression of steps. The order can be different based on a person's background, experience, and knowledge - I have listed Steps in the order I would probably have progressed through - i.e., if Step 1 shows no change, do Step 2. Step 2 shows no change, on to Step 3 - I think you get the idea. One thing I was often good at was asking questions of the people I worked with, be they hardware people or software people, that jogged something in their memory that led to a solution.

Step 1) Swap in new PCB - You did this with no change in operation reported.

Step 2) Put suspected PCB in a know working engine? Runs okay on same track that "delayed startup" engine is run on?

Step 3) Testing power path from Track to PCB

Step 4) What is plugged into the PCB, besides power from the track? Can I remove one plug at a time from the PCB to see if the operation changes?

Step 5) Did you change the track power source between the time you had the normal operation and the "delayed startup" operation? i.e. - change transformer the transformer that supplies the power. (example: change from postwar ZW to ZW-L)

These are the 5 Steps I can think of at this time. You did Step 1 with no change in operation, so maybe the other Steps will help shed more light on your problem