Hello everybody,
I'm new to this forum and I'm sorry to be looking for help here already with my first post. I'm not sure this is the right place, but I really don't think there's many other sites out there that gather as many electronics enthusiasts and professionals as the EEVBlog does
I'm not really a newbie when it comes to electronics, soldering and stuff... I've been handling soldering equipment regularly for the past twenty years or so. But still, my experience with circuitry is pretty much limited to digital stuff, where there's either voltage or no voltage... I don't have much practical experience with analog circuits, which I believe is what I'm lacking in the given case.
What I have sitting on top of my bench right now is the drive motor assembly of a somewhat older train destination display that used to be installed on pretty much every station on the local subway / tube / underground (I'm not sure what term to use... we call it "U-Bahn" here) network here in Munich. I remember them myself until a few years ago, when they were successively replace with newer, modern LCD displays. The design of this unit might date back into the 1980s or even 70s (1971 was the year when the subway started operation in Munich; however I'm not sure if these displays were already in place back then).
The challenge, of course, is to get it working again in some kind of way... and that's where I'm lost. I can't really get the circuit at hand to work in any useful way, and my hope is that somebody here will recognize some pattern, or derive in any other way how to drive the inputs in order to make it work the way it's supposed to.
I'll try to provide as much detail as I can about the circuit, but first: here's a short video of somebody who claims to have repaired one, just so you get an idea of what I'm talking about:
In the comments there's a reference to a website (that is gone by now) which was supposed to contain more information about how he did it - unfortunately there was not much information there, and we never managed to get in touch with the uploader.
Speaking of "we": I got this drive unit from a friend who is an active member of a local society called "Münchner U-Bahnfreunde" (German website:
http://www.muenchnerubahnfreunde.de/). They are striving to collect historical data, photos and items, and they also feature displays at local fairs, where they show off their collection. They bought a few of these old train destination units, and they are already putting them on display regularly, even though non-functional. They asked me to try and "resurrect" the old circuitry inside. The basic idea here is to combine the old electronics with something like an Arduino and / or Raspberry Pi (or whatever it takes) and let the fair attendants control the display in some way.
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Alright... now for the stuff I know so far. I'll attach some pictures to clarify things, due to the file limitations I have placed the complete imageset here:
http://www.justjakob.de/zza/. You can also find the Eagle schematic there. If there's any questions go ahead and ask, I will of course try to answer them
The unit consists of a rather chunky 3-phase motor, a set of gears with some magnets on them, and a PCB that has a 10pin connector for an input. Whatever once was connected to that input has been lost, but from what I'm told I suppose it wouldn't make things much simpler.
I have tried to reverse-engineer the PCB and look up the components on it, I have attached a screenshot of what I worked out. Also check out the image link above for the Eagle file.
Here's the parts list and what I know about each of the components:
MOTOR: "Berger Lahr" RSM63/12 - That's the primary drive motor, a 3-phase synchronous motor. the closest kind of documentation I could come up with is pages 101 and 102 of this document:
http://www.schneider-electric.com/download/ww/en/details/2081705-Synchronous-motors-RSM/?showAsIframe=false&reference=1148964249C2 & C3: appear to be motor caps that allow the 3-phase motor to run on single-phase AC. I don't have their exact capacities, but I remember that they somewhat matched up the values in the motor datasheet.
C1: I'm not sure if that's a capacitor at all. It's marking reads "104 M3B" and I couldn't come up with any information about it. Might as well be some kind of fuse / MOV.
T1: marked "L201E3", appears to be a TRIAC to drive the motor AC.
http://www.alldatasheet.com/datasheet-pdf/pdf/114977/TECCOR/L201E3.htmlT2: marked "MPSA92", seemingly a PNP transistor.
http://www.onsemi.com/pub_link/Collateral/MPSA92-D.PDFT3: marked "MPSA42", seemingly a NPN transistor.
http://www.farnell.com/datasheets/1747986.pdfIC1 & IC2: marked "03F024", can't find any information on them, but I guess they are some sort of hall effect sensors. They are mounted on the copper side of the PCB, right underneath a big wheel that sits right on the motor hub, that has permanent magnets sitting on it.
There is also another component that I forgot on the schematic. It's marked "S14K 60" and sits parallel to C2 & C3. It seems to be pretty clearly a MOV that - if I understand correctly - is for protection and probably does not influence the regular function... correct me if I'm wrong here.
My guesses about the magnets and hall effect sensors is that they provide positioning feedback to the controlling circuit. The math adds up: There's four magnets on the outer diameter (the one that IC1 picks up) on the motor wheel, the gear train reduces the motor movement by 1:10, and there's a total of 40 display "sheets" on the display hub, so each magnet passing would mean that the display has flicked by one sheet.
There's one more magnet on the inner diameter of the motor wheel that mechanically interacts with the 1:10 reduced wheel on the gear train: It is pushed down (near the hall effect sensor IC2) only on full turns of the reduced wheel, which would correspond to a full run-through of the display sheets. That seems to be some kind of calibration input for when the unit is powered up since the output of IC2 is routed directly to the 10pin connector and has no other connection to the rest of the circuit.
I tried to measure the output of IC2 with a multimeter (I don't own a scope, unfortunately) and it seems like it is actually pulled to ground when the magnet comes close to it.
From what is written in the copper, it seems the circuit used to run on two different voltages: 42VAC for the motor and 15VDC for the rest. I have tried to get some life out of it and could get the motor to actually spin when applying the voltages directly to the TRIAC, so I believe there should be some way to get it to work.
The 42VAC most certainly go into pins 2 and 4 of the input, at least that's what makes most sense to me. That way T1 can be triggered to close the actual motor circuit. The big question is: How do I trigger T1?
I don't know exactly where the DC is to be fed into, for me the most obvious combination would be pin 6 to be positive and pin 1 to be ground (derived from the guessed power supply lines of the hall effect sensors). Might of course be wrong here.
I have no real idea how to drive the remaining pins, unfortunately.
I can see that there's some interaction between the hall effect sensor IC1 and the transistors, and I'm really not sure how it's supposed to work. My guess would be that you can drive this circuit in a way that stops automatically at the next pass of the magnet (which would mean at the next sheet of the display) but I can't really "see" that behaviour in the circuit. Also, my guess could as well completely wrong
I'm also guessing that there is some kind of way to read the magnets passing by IC1 externally, since it would be kind of hard to stop the motor at the right time otherwise. With all the passives attached to IC1, I'm not sure how that works either.
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I guess that's all the detail I have at this point. Sorry for the long post, I just wanted to make sure that there's nothing missing in the puzzle. If I have overlooked anything, please let me know, I'll try to fill it in.
One more thing: Yes, it would be feasible to design my own PCB and attach the motor onto that, and I have spent some time thinking about that, too. I consider this as a "plan B", given the historical background of this project I'd rather keep as much of the original components, of course.
I really appreciate any help I can get with this project, thank you all for reading up to this point, and thanks in advance for any input