TMCC gantry crane question

Does anyone out there have a TMCC crane that can tell me if this hum is normal?  

I have a TMCC Crane and it doesn't make a sound I am aware of. You might open up the controller and poke at it with a Q tip and see where the hum is coming from. I haven't opened mine up but would assume there is a power supply that converts AC to DC for the TMCC circuitry. Maybe a filter capacitor is bad.

Pete

I will have to try that, the thing that is weird to me is that not only does the controller hum, but the crane does too.  There is a small capacitor connected on each motor (at least I think that's what they are) and looking at the exploded diagram it appears that there's a diode bridge in there as well.  Maybe that's the source of the hum on the crane?

Mine never hummed.  It was silent while not in operation, and never hummed while it was.  Running in TMCC old school with an AMC.  Always worked great.  Good luck.

So I believe I have narrowed down the electrical hum to a resistor in the controller (the blue item in the pic) and a capacitor on the motor.  I am not for certain but as best I can tell the noise is coming from there.  The blue resistor gets fairly hot when power is applied.  Is this normal?  The buzz could possibly be coming from one of the two silver cylinders near the blue resistor. I am not sure what those are.  I will try to test the resistor tonight with my multi meter but would a bad resistor cause this electrical hum?  Or possibly bad capacitors (i assume they're capacitors on the motors)?  Sure wish I wasn't an electrical dummy!

I believe the blue component is actually an inductor. These are usually placed in series with a load to filter high frequencies, much like a capacitor in parallel. If you measure across it with an ohmmeter it will likely read an ohm or less. Without reverse engineering the controller I would guess the inductor is getting hot because there is a problem in the crane itself. You said the hum goes away when you disconnect the controller from the crane further indicating a problem in the crane. You could simply unsolder one lead from the motor capacitor to see if that what is causing the problem. Report back after trying that.

Pete

So I experimented like you said and took the capacitors off the motors and it still buzzes. I believe it's actually the motors making the buzzing noise.

I experimented removing the capacitors and their accompanying wires in the controller and it looks like it's the capacitors making the buzzing noise in the controller.  More than one buzzes.  There is a diode bridge in the crane. Is that where it converts from ac to dc?  I wonder if it's not doing its job and that is causing the buzz. However if it wasn't working it seems like the motors wouldn't work properly either.

I have the same TMCC crane and mine emits a soft buzz as well.

I've just always assumed that it was due to the TMCC wiring.

I believe if it has an objectionable buzz, it'll turn out to be filter capacitors or a diode in one of those bridge rectifiers has died.  Those "silver cylinders" are filter caps.

So i hope i found the culprit.  I took the bridge rectifier off of the crane and tested it with my multi meter.  One leg read much higher than the others which to my limited understanding signifies a bad rectifier.  This would make sense what you said John regarding DC vs AC voltage on the motors.  John, i didn't realize there were also bridge rectifiers on the controller board.  Can you explain to me which components are the rectifiers?  I thought the tan discs were capacitors?  The bridge rectifier in the crane was a fairly large square piece with a wire coming out at each corner.  I ordered a new rectifier and when it gets here I'll let everyone know if that solves the issue.  It may be a rectifier in the controller though as depending on whose directions I follow on testing the bridge rectifier, it may not be broken.

The bridge rectifiers are on the back side of the board, you can see them in the silkscreen labeled BR2 and BR3.  I'd suspect one of those could be bad, or the filter capacitors that smooth the outputs.

I will take a pic when i go on my lunch break to verify with you, but the back side of BR2 and BR3 are screw terminals to connect power (BR3) and the legacy base (BR2).  The blue resistor is connected to the power terminals.

OK, with no information to the contrary, I figured those could be bridge rectifiers.  That's the risks of having a tidbit of information and no way of seeing the rest of the board.

Try checking the diodes in this area, you should be able to check them in-circuit.

I didn't realize those were diodes... Are the ones that have the triangles next to them the diodes?  I will check those as well.

Many of the components have a marking next to them on the board. "C" is a capacitor, "D" is diode, "Q" usually is transistor or some sort of semiconductor switch. "R" for resistor and "L" for inductor. One test you can do with a multimeter is read the voltage across the can capacitors. Set the meter to AC volts and read what you get with the crane disconnected, no hum, and then with the crane connected and you get the audible hum. With the crane not connected you should get less than 20 millivolts, maybe close to zero. Then read what it is connected.

A reading higher than 20 mv without the crane connector could indicate a bad bridge or capacitor. This is not an exhaustive test but just a few things to try with a simple meter.  Someone with an oscilloscope could solve this in a few minutes.

Pete

Trying to debug this stuff with limited pictures and no access to simple diagnostic readings is a crap shoot.

Aw come on John you know you like troubleshooting in the dark   I appreciate everyone's suggestions and help,  I'll try them tonight and see where I get.  I'll probably end up having to send this out to someone who knows what to look for.

With 15 minutes of lunch time to spare I tried a couple suggestions and this is what I found:  First of all, i checked all the diodes using the multimeter and they all read in the 500 range one direction and 0 in the other, meaning they are working properly if I understand correctly.  Well, just out of curiosity, I powered up the board and then checked them again.  They all did the same thing, reading around 500 in one direction and 0 in the other, except for one diode.  That one still read in the 500's powered up, but when i switched leads, it read in the 300's the other direction.  It is D3 that did this. You cant see the D3 in the pic as its hidden under the capacitor nearby.  Since it was powered up I don't know if this means anything.  I then used my meter to check the two capacitors as suggested by Pete and I have attached some pics of those results and i'm not sure what to make of it.  Both capacitors gave the same reading whether the controller was hooked up to the crane or not.  Also, one interesting note, i had previously removed the bridge rectifier from the crane last night, leaving the wire ends not hooked up to anything and the crane motors and the controller still buzz.  I'm thinking that bridge probably isn't bad.

You guys are managing to run some trains at some point?

The power circuits on most of these devices is:

(R?, the blue 110? ohm resistor is probably in series with the following power circuit.)

AC power feeds thru (R? & D4 for halfwave rectification.  Z1 is a clamp TVS across the output of D4 for overvoltage protection. 

The halfwave voltage then goes through a 12V regulator chip U7 that lops off the peak of the sinewave at 12 volts to absorb part of the input power and provide a 12V supply.

The 12V regulator feed through D3 to a 5V regulator U? that powers the logic circuits.

Check the DC voltages on the two can capacitors.  You have shown us the AC voltages.  I forget exactly where they are attached in the regulation chain.

The above architecture is used in almost everything that evolved from the original TPC3000.

The DC voltages are as follows

The smaller can is 28.0 and the larger is 11.1 

The bridge rectifier on the cab base is for the magnet .

Good to know, I can eliminate that as a problem. Thanks

Based upon your measurements, I would expect the small capacitor to see the incoming halfwave voltage, and the other capacitor to be after the 12V regulator and diode. 

So do they seem to be in working order based on those measurements?  Any idea why the disc capacitors are humming?  

I don't know how those disc capacitors are used in the circuit, but they may be across the switching devices (which we can't see hidden under the capacitors?).  If indeed they are connected that way, they will have a voltage across them when the load device is OFF.  Those capacitors are ceramic capacitors, and they experience electrostriction, meaning that they expand and contract as the voltage varies across them, which might cause them to hum.  The effect is similar to how the bimorph discs that "beep" in a CAB-1 work.

The voltages seem appropriate.

This is a picture of underneath the capacitors. Not sure if it will help at all.

The four Teccor L2004 chips are the actual switching devices that control the motors.  The yellow disks are not capacitors, but rather Polyfuse self-resetting fuses.

So knowing those are polyfuses any insight as to why they would be buzzing? So from what i can tell some sort of circuit is being completed through the can motors and supplying return voltage to the controller.  I believe that return voltage is causing the polyfuses to hum because if I disconnect the crane, the buzz goes away.

I suspect something is causing the circuit to always draw current.

Try taking a long plastic rod of soda straw and holding one in contact in right in front of your ear, touch the other end to each component.  This is an old mechanics trick, the buzzing will be a lot louder when you touch the actual component that is making the noise.

A polyfuse should be a fairly good short circuit when it is not overloaded.  You could measure the AC voltage across each of the polyfuses while they are humming to see if there is any voltage drop.  There should be at most a very small voltage drop.

If you do measure a significant voltage, the polyfuse is either defective or it is properly operating in response to an overcurrent condition.

Since the crane works, it's hard to believe he's getting an over-current to the polyfuses.  I confess, I've never heard them sing, and I use them quite often.

I will check the current on the fuses just to be sure.  I also noted last night while troubleshooting that when I remove the small capacitors on the motors, the buzzing increases and when I reconnect them the buzzing reduces. There is also a large capacitor connected across the bridge rectifier for the magnet that does the same thing when connected and disconnected.  It seems as if when I remove the capacitors another one of the polyfuses begins buzzing and when i reconnect them, one of the fuses stops. This was the case with both motor capacitors.  I have also uploaded a quick video clip to let you hear how loud the buzz is.  As John said, the crane works just fine aside from the loud buzz that makes me worry it could blow at any time! By the way, I have tried more than one transformer just in case that was the problem.  It is currently hooked up to a K-line power chief.

If the buzzing goes away for a motor when you reconnect the capacitor, have you tried a new capacitor across each motor to see if you have one or more bad capacitors?

The buzzing only reduces in the controller, the motor still has a quiet buzz with the capacitors connected.  Connecting and disconnecting both capacitors just changes the amount of buzzing in the controller.  I am probably going to go ahead and order new capacitors for everything if they're not too expensive.  However, those silver capacitors on the controller are different than normal ones as they have a plastic base on them or something that solders on the sides, not through the circuit board (no protruding wires).  I haven't been able to locate a comparable replacement on those.

You can change the caps but if you use the same values I am not sure it will make a difference. I still think the AC ripple across the caps is high when the crane is not connected. Dale mentioned half wave rectified (single diode) but if you actually have two full wave bridges the ripple should be much less. Before ordering new caps just replace the bridges if you are not sure if they are good or bad.

Pete

when you say to replace the bridges, are you referring to the little diodes D3, D4, and Z1 in the pic?  As I noted in an earlier post, those diodes all read in the mid 500's in one direction and 0 in the other, signifying they are working properly, but when powered up, D3 also registers a reading in both directions.  Nobody has mentioned if this is normal or not.  

I am getting a little lost in this but you said further up the thread you had ordered new bridges.

Pete