new ps 2 board problem

Hi Marty, thanks for the reply. Both boards are new from mth, the malfunction occurs on two different mth test jigs so it appears to be the board. A known good power board was swapped and results were the same, runaway speed and no sound over 11volts, conventional mode. Original problem reportedly caused by using wrong tender, no way to verify. This is a 3volt system. Also there is a .5 amp increase from 10to 11 volts, ie 1.2 to1.7 amps. The sound was loaded by mth, I reloaded it successfully but it did not fix the problem. If I had to guess I'd say some component is causing an intermittent power surge causing the motor to race beyond the tach readers ability to process the pulse, but I have no idea what the part might be. Hope you can give me some direction on this, you have helped me in the past. Boards are under warranty and can be returned, but then I don't learn anything. Thanks
Regards,
Joe

Joe,  I Have seen one sound file where the motor speed on the test rig (which is unloaded) is too fast for the tach reader to keep up and you start missing counts.  Normally it was at a higher voltage than 11V, closer to 13-14V.

 

I would install in the engine which is loaded and the motor spins slower.  See how it does.

 

If it still acts up at higher voltage, I would say you have a Processor problem.  I have one on the bench that didn't have the run away issue but would  run up extremely high amps after running for a few minutes with a good load on the engine.   G

Picking up on G's comments, I'd run the engine at 10.5V or some voltage where the chuffing still works.  Presumably you have conventional mode speed control in the default "on" setting. 

 

Then, insert a piece of opaque paper between the tach-reader sensor and the flywheel.  This should block tach pulses and the motor should speed up to full track voltage - hopefully 10.5V is enough spin the motor fast enough to lose the chuffing.

 

If experiment is "successful" then I'd fiddle with the distance/alignment of the tach sensor board.  Presumably you've already inspected the flywheel striping for distinct, clean, black/white striping. The opto-sensor chip on the tach board is an analog component and there are production variations in sensitivity.  You could have a "weak" chip that can't keep up with faster pulses. 

 

Hi George, thanks for chiming in. The problem first occurred after the new boards were installed and it was put on a test track, so it was loaded with  the weight of  the engine and tender, plus it  is an intermittent problem, every once in a while it will function normally but only for a short while. I agree with you that it could be the processor itself, any way to test it w/o swapping it out?  thanks.

   Hi Stan, thanks for the input. I had put the boards on two different test jigs and the results were the same, so I don't think its the tach reader. The test jigs were used to check other  boards and they both work fine. Thanks.

Regards,

Joe

Ahh, I just learned something!  So the test-jig you guys talk about has a motor (unloaded) with a tach-sensor. Got it.

 

Then how about this. Pull the 5-contact motor connector from the PS2 board. Now you can directly drive the test-jig's DC motor from a variable DC supply (if you have one).  Or hook up a diode or bridge-rectifier to make DC from a variable AC track transformer.  Run the voltage up and down to spin the test-jig's motor at different rates.  The PS2 boards should chuff even if the motor is being driven externally.  That is, you can run the boards at a relatively low-voltage yet have the speed at the "high" voltage that apparently triggers the problem.  This may be more trouble than it's worth if you don't have a DC supply but if you're interested in learning I'd think this might reveal something.  Just an idea...

 

 

Hi Stan, that's some good "outside the box" thinking, I like it. You could also drive the motor with  a dremel tool with a rubber washer fixed on it. The result would still point to the board ie the processor.  To add insult to injury, now there is only idle sounds no matter how fast or slow the motor turns. Intermittent problems with varying symptons are the worst to troubleshoot, time to let MTH replace the boards and go from there. If I learn anything usefull I will post it here for you guys. Tnanks for the input.

Regards,

Joe

Joe, I would reload the sound file. See if that solves it.  If it still acts up it has to be a processor problem since changing PS doesn't resolve it.  G

Are you an MTH authorized service tech? Seems like you are spending a whole lot of energy to resolve an issue that is better handled with a warranty RA

George, one of the first things I did was to reload the sound file successfully.

Matt, no I am not.

Regards,
Joe

Joe,  I would call MTH and see if they would honor a warranty anyway.  Just reread your original post and see you tried a reload.

 

Assuming the power supply works with a different processor fine, and this processor doesn't work with other power supplies it is time to send it back for replacement.

 

It can be anything from the main processor, smaller micro chip, control FET or the Motor FET not turning off properly.  It would be an easter egg hunt, so sending it back is best.   G

George,  I will get new boards from  MTH, you are right its easier. The sole purpose of this thread was to understand the problem, and to find out if there was a reasonable fix, and how to trouble shoot it, make  sure I didn't miss  anything. The suggestions here were helpfull and I thank you and the others for your help.

Regards,

Joe

Joe, Once isolated to the processor board, something sporadic like this is hard to nail down.  If something is not working, like a light or  heater, or motor always running, that can be isolated.  Motor control gets a little tougher and sometimes it is a bad processor segment.  No fixing that.  G