TAS Engineer On Board Problems

I have had several Engineer on board systems go south. Time is taking it's toll on the boards as the years go by. Have had several issues with the cruise control on these now dated boards.

The symptoms suggest the board is indeed going south.  I have fixed several of mine, but they're getting long in the tooth, and it gets harder to justify keeping them running.

Did you check the gap between the sensor and the tach strip? Its fairly critical and should be .030". You can use a drill bit if you don't have a set of feeler gauges.

Pete

He stated that the LED is blinking for each stripe on the flywheel when he rotates it, so I suspect it's probably close enough.

"As best as I can tell I have lined up the black ends evenly & the optic is triggering at every bar."

Thanks for the quick replys. I'll try setting the sensor gap again.  I have couple questions still.

First: does the sensor see the white or black or does it really matter?  Looks to me like the red LED is actually turning on, on when the white part passes (gets its reflection). I imagine the EOB only cares about regular pulses from the sensor board.

Second: is it usually the sensor board that fails or the main board?

The sensor just converts black and white to ones and zeros. This is a reflective sensor so white reflects the light back and turns on the photo device (transistor, diode?? doesn't really matter) on. I assume you are seeing the red LED with the shell off. If you run it at speed is it still blinking at a regular rate or does it stay off or stay on?

All the failed EOB boards I have seen fail around the power devices including vaporized circuit traces. Never had a problem with the tach circuitry other than adjustment.

Pete

I've actually had several that ate their uP, which is a show stopper.  However, the triacs and the power traces are the more common failure.  Those are not that difficult to fix, but it's a PITA to fix the triacs, you have to pull the whole works off to get to them.

Norton:  At a crawl in cruise off mode the red LED appears to be blinking consistently anything faster and I can't tell.. might be because the motor is turning too fast for my eye. 

Gunrunnerjohn: Do the triacs stick on? Is that why the engine takes off at full speed?  The engine runs fine in cruise off mode - no full speed take offs. 

First off, check the wiring between the tach reader and the EOB motherboard VERY CLOSELY!  I've seen a number of them that have a broken wire between the two units, if the signal wire is broken, you'll get the rocket effect.

The fact that conventional works is simple to explain, you're just passing the variable voltage through, even if the triacs were shorted, it would still run that way.

Usually, only one set of triacs is bad, though I replace all of them if I have to remove the heatsink.  That being the case, the locomotive will frequently run properly in one direction, but take off in the other.

The Horn and intermittent running suggests a control circuit issue.  I'd remove and replace the PIC processor in it's socket to make sure it has good contact, and I'd try a different R2LC. 

Cruise off in command mode would be a good way to test the integrity of the triacs (and everything else other than the two cruise modes).

Very good point Norm.

It has been runing fine in command mode cruise off. I reseated the PIC, don't have another R2LC around to test right now.  After I reseated the PIC, I noticed the tail of the tach tape had lifted, so I glued it down. After that I ran it forwards and backwards for about 20 min each direction in the first speed step. I need to  run it more and at faster speeds to see if it stays good. 

Also, I tested the connections from the sensor board to the motherboard. They tested ok I think. 5v on black and red on the sensor and about 1-1.5v on the blue wire on the motherboard plug while the red LED was lit up.

Reseating the PIC was probably the silver bullet, after some years, the contacts tend to oxidize and cause issues.  The same thing happens to Lionel RailSounds audio boards, reseating the two chips fixes a lot of these.