Atlas/Tomix vacuum car problems

[Maletrain]

Years ago, I bought a new Tomix vacuum car to clean track.  I am just getting around to converting it to DCC, which looks to be pretty easy.  Now that I have mentioned that at the club, others are bringing out their non-functioning versions for me to "look over".  I took apart an Atlas version today, and found that the Off-On-CL plastic switch part that protrudes from the top of the car is connected by two small plastic pins to the plastic part that holds the actual electrical contacts.  Those pins are broken, so the unit cannot be turned on.  Those pins are fragile and that seems to be a common failure point.

I tested the motor with a 9v battery directly on its contacts and it worked well.  So, I cleaned the contact points in the car's current path, set the switch contacts to "On" and reassembled it to see how well it vacuumed.  Not well at all.  There is some sort of electrical controller in the onboard chip that shuts down the motor before it gets enough voltage to actually suck test lint off the track.  In comparison, my new one will go to a much higher speed and does suck up even largish (but light) particles.

So, I am thinking that the OEM electronics are toast, and am wondering whether it is worth stripping them out and converting this one to DCC.  Is the real problem likely to be in that chip, or in the motor drawing too much current to let that chip be happy?  At the same DCC voltage setting, the new one spins much faster.  And, it goes even faster at the higher voltages tolerated by the chip in the new Tomix version.

Looking for experienced suggestions from others here before I spend time on any of these.  In particular, I am wondering how the DCC version fairs when used on a DC layout.  I would leave the analog mode active in the decoder.  So, on a DC layout, I would expect the vacuum motor speed to be linked to the speed that the car is being pulled along the rails - high suction only at high speed.  Is that worth the effort for somebody who will only use it in DC mode?

[peteski]

I have one of those (quite old - probably original release), but I haven't used or looked at it for some time.  I would have thought that the only electronics would be a bridge rectifier.  IIRC in DC the the vacuum motor's speed (as expected) would depend on the DC voltage coming from the track.

The standard permanent-magnet DC motor (similar to ones used to power N scale models) under a decoder control should respond to the DCC throttle controlling the decoder. In DC it should again run at a speed proportional to the DC voltage from the decoder. If it will only be operated in DC then IMO installing a decoder is a waste of a decoder.

[Maletrain]

In DC, the only value of a decoder would be to get rid of the OEM chip that keeps shutting down the motor.

But, do I really need any chip/decoder?  It is just a DC motor. 

Why not just connect the motor straight to the track if it will be operated only on a DC layout?  The OEM version chip seems to be intended to use some sort of "constant lighting" power to the track of DC systems (AC on the track?)  that would allow the vacuum motor to run at high speed while the car is not being pulled rapidly by a DC loco.  So, maybe there is a rectifier in that OEM chip, along with some sort of over-power or over-heating detector?

Frankly, the whole thing seems weird without a decoder for setting the vacuum fan speed independently of the speed along the track.  But, the OEM version is DC only, according to the literature.

[nickelplate759]

I put a decoder in mine and it sucks nicely.  As I recall I used a cheap 2 function digitrax decoder.

[peteski]

I don't think you need a decoder for running in DC.  But will the motor produce suction running in either direction? If not, a bridge rectifier would assure that the motor runs in the correct direction regardless of the DC track polarity.

I'm still curious why some additional electronics would be needed for running a simple DC motor the first place.  Is it possible that the motor is rated for lower voltage and the electronics are a simple voltage regulator?  I don't recall the details of my vacuum car and it is buried somewhere. 

The other issue is that the car needs to be pulled by a locomotive.  To get the motor to run at high enough speed to suck it needs higher voltage, but then the DC loco pulling it will be going at a breakneck speed. 

[nscaler711]

I put a  DZ126 in one and I haven't had any issues. just red and black for track power and orange and grey for motor, bypass the switch entirely. polarity should not matter. the blades of the blower are not angled. I have pretty decent luck at speed step 60-80. I think the DZ126 is dual mode so it should work either way. there is a slot in the weight where you can nestle the decoder in fairly well too. 
If you decide to put a decoder in it, then it can be used pretty much anywhere and the simple small decoders are fairly cheap now, so it's not a complete waste of time or money.

[C855B]

... will the motor produce suction running in either direction? ...

I have two, one converted to DCC. Answer is "yes". The impeller vanes are straight, so air movement is by centrifugal action only. Makes me wonder if I ought to 3D print a scroll rotor that would be more efficient if run in the same direction with the car moving either way.

Mine works nicely; there's always something to empty out of the catch chamber. I did the conversion years ago, so I should open it up and see how I did it. I did remove the selector switch on top. Silly and fun thought - with the hole there maybe I can stick an LED it it and wire it to one of the unused lighting leads for a flasher. I've done worse things.

[Maletrain]

I am definitely going to put a DZ126 in the new Tomix version that I own.

My questions really are coming from what to do with other members' Tomix and Atlas versions that are currently not working.  If it is just a switch with broken plastic prongs, I will have one from my conversion that I can give to ONE member.

But, the strange performance of the Atlas one that will not run fast without shutting down is something that I  think I can fix by just wiring the motor leads directly to the track pickups.  The owner of that one does not use DCC, but the fact that I found the box for it under the club's DCC layout makes me strongly suspect that somebody "tried it" on the DCC layout (without converting it with a decoder) and damaged the OEM chip, then gave it to the DC layout.  So, if it is only going to be used on a DC layout, which does no have that "constant lighting" mechanism anyway, why get fancy with an on/off switch?

Regarding the impeller rotation direction, a rectifier in the circuit would solve that if it mattered.  But, the OEM impeller works the same in either direction because the vanes are straight.  If somebody here decides to make more efficient impellers, there is room to add a rectifier.

[peteski]

I'm (as usual) curious. Could you post a closeup photo of the circuit board with the defective chip?  Not sure it will give me enough info to tell what the circuit is supposed to do, but worth a try.

[John]

I'm (as usual) curious. Could you post a closeup photo of the circuit board with the defective chip?  Not sure it will give me enough info to tell what the circuit is supposed to do, but worth a try.

this might help

https://www.hookstonemodels.co.uk/dcc-conversion/tomix/track-cleaner/6425

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[Maletrain]

OK, here are (crappy cell phone) pictures of the top and bottom of the board:

On the top, the 3 position switch contacts are visible along with a cap marked "SX6A Mexico" that I initially thought just bridges the track feeds, but looking more closely at the traces, I now see feeds the chip on the bottom.



On the bottom are 3 more components:

1.  Looks like a surface mounted resistor (or cap) across the motor contacts
2.  Looks like a diode marked "445   4.7   35V"
3.  The 4 contact chip marked "Z64"



Remember, there is some sort of "Continuous Lighting" (CL) Power feature that is one of the switch positions, and is not supposed to be used when that feature is not available.  On this vacuum car, that position is counter clockwise from the center, which is "On". Clockwise from the center is "Off".  (directions when looking down on top of assembled car.)

The directions state that the DC power should be at "low speed" when using the "CL Power" position, but then says "*except Suction Fun (sic) Disk"  (I think they meant "Fan Disk"  )

Elsewhere is states that using "CL Power Mode" for cleaning operations other than the vacuum, the "safety circuit will work in a short time to stop the operation."

The problem I am having with this Atlas unit is that the "safety circuit" seems to be cutting in even in the plain "On" model with a DC track voltage of only 7.5 volts when using the vacuum disk.  That isn't fast enough to pick up anything from the track.  Putting a 9V bsttery directly across the motor leads with the motor isolated, the motor runs fine and faster.  So, this "safety circuit" seems to be cutting things off at too slow a speed.  Doing the same thing with my new Tomix vacuum car, the motor goes to high speed in the "On" mode and does not cut out.

I do suspect that the Atlas car was "tried" on the DCC layout some time in the past, didn't work there, and was given to the DC layout.  That may have damaged the "safety circuit" and account for this problem.

[John]

looks like a bridge rectifier and capacitor is all that's there

[Maletrain]

John, Those items alone would not provide a safety cutout circuit.  Wondering about that diode (if that is what it is).

[peteski]

I see no diodes besides a bridge rectifier.  There is an electrolytic 4.7uF 35V capacitor, a small MLCC type capacitor (the very small tan color part), and the M&M-like yellowish device on the other side of the board is likely a PTC circuit protector or resettable fuse.  That it likely what is causing the problem. Temporally solder a piece of wire between its solder pads (it can remained soldered) to bypass it to see how the circuit behaves.  The bridge rectifier also appears to be burned slightly?   Might be just the way it looks in the photo.

To further explain, the MLCC across the motor connections is for RFI suppression, and the 47uF cap is actually not connected directly to the motor. Maybe it is for that unused option you mentioned.  The PTC resettable fuses are often used to protect the motor from excessive (stall) current damaging it. I have seen these yellow discs in Bachmann 44-tonner and other locomotives from various manufacturers.

[Maletrain]

Peteski called it!

I soldered a bridge wire across the pads for "the M&M thing" and now the motor goes much faster at the 7.5 volt setting and does not trip off all the way to 12.5 volts.

Thanks for the help and learning process.

BTW, the other side of the "M&M" also has printing that I missed earlier.  It looks like "X60" and "X025", except the "X" in front of the "60" is probably not supposed to be an "X" - the character is wider than the other "X" and it is like the top "v" and bottom "^" overlap in the middle and are filled inside the  overlap diamond between them.

When I convert my own Tomix version, I will have one of these "M&M" things left over that I could use to replace the bad on in the Atlas unit. 

But, is that really worth the trouble?  Is anything likely to burn out if some object stalls the rotor?  The motor is a robust looking open sided 5-pole.  I am not thinking that the rectifier and the electrolytic cap are in the basic "On' circuit - thinking those are there for the "CL-Power" mode, only.  But, I have not followed the traces on the board to be sure of that.