I bought a 2nd hand self levelling laser from eBay and it was an incredible bargain (Leica Rugby 100) although still quite a lot of money. The seller said the batteries were probably flat and when I unpacked it, that was the case (it takes 4 D-cell 1.5V batteries). Instead of just going out and buying more, I hooked it up to a 6V fire alarm battery and in my living room, it worked just fine, the levelling motors doing their thing and then sending a rotating laser beam around the room.
However, this cackhanded idiot thought he'd try it outside on a tripod (as they are designed to be operated) but the battery hookup was a bit fragile and unwieldy. Long story short, I think I might have momentarily reversed the polarity and now the levelling motors don't turn.
To explain how these things work, inside you have 2 spirit level vials (one for each axis) with an optical sensor and an LED. These move the laser gimbal and once the level criteria is met, the rotation motor and laser get turned on, sending a lighthouse style beam around the environs. There is also a manual mode whereby the laser spins and the motors can be individually controlled to provide a tilt (the tile function doesn't work either now although I do get a laser level... that isn't level).
I've tested the motors and they're fine - I think they're driven by a couple of FDS8958A MOSFETs as they obviously need to reverse direction to turn the screw jacks. If I take the drive belts off, you can see the motors being turned very slowly but without enough speed or torque to actually turn the associated screws (via a pulley each). There are no obviously burnt components on the 3 circuit boards (one of which is a speed controller which works fine) but there is a very faint high pitch whine as it tries to turn the motors. I don't know if this is normal or whether it indicates a problem. There are some SMD tantalum capacitors - are these likely to be a failure point and are they possible to test without desoldering them?
I'm not sure if I'd be able to reverse engineer a self levelling circuit using an Arduino or whether I'd be better served hacking in manual motor controls but open to ideas/thoughts
The quote I've had for fixing it was roughly 3 times what I paid for it - would work out cheaper buying a new one, frankly. The individual circuit boards don't appear to be available as spares. Maybe I'll see if I can hack it with an Arduino although knowing quite what signals the optical sensors give out will be a challenge without an oscilloscope.
That is a nice piece of equipment, if it were me, I would take a run at fixing it because I have had a lot of success with things after i was told that I needed to replace the item. I saved myself about 5 grand on one of my boat air conditioners. The expert said the circuit board was shot and I needed a whole new unit. After a little poking around in the board, I found a relay that was not working properly and replaced it for $12.
Recently, and this is crazy, my most important USB thumbdrive stopped working, nothing. I tried it in every computer half a dozen times. It was dead. I had a lot of important drawings on the drive so I thought what the heck, I pulled it apart and started looking. I did not have any idea what I was doing other than I thought if I found something obvious I could try replacing/jumping over the offening part. You know, fools rush in where angels fear to tread. I started testing the resistors which all seemed fine. I plugged it in a few times to see if it was working. No such luck. My meter has a capacitor tester so I gave that a shot. I tested a couple of capacitors, plugged it into my computer and the damn thing lit up! I was able to download all my stuff. For whatever reason had I allowed myself to simply accept that the thing was dead I never would have recovered my files.
The tantalum capacitors tend to fail spectacularly. I wouldn't just assume the speed controller is working fine, as it is part of the problem circuit. Test it and make sure. See if your scope picks up the signal from the controller to the mosfets. Make sure the mosfets have power on the source/drain. Since it's spinning both directions, I would think it's an h-bridge driving the motors.
The problem is that a lot of ICs use diodes as part of their ESD protection. Power MOSFETs will also usually have a body diode between source and drain. These diodes are reverse biased when used with normal polarity, but when the power supply is reversed they become forward biased and are basically a short. Any one of them could blow and it's hard to predict what the effect will be. One of my classmates reverse-polarized a 741 op amp (he misinterpreted "reverse the inputs" as "reverse the power") and the chip actually blew up and blasted a fragment of the plastic package up towards the ceiling.
The repairability depends on what exactly blew. If it was just some capacitors, semiconductors, or non-programmable ICs, you have a good change of repairing it if you can find compatible replacements. If it's the microcontroller, you're pretty much screwed.
Recently, and this is crazy, my most important USB thumbdrive stopped working, nothing.
I have never allowed my USB drives to have the only copy of important files. Not only are they easy to break, they're easy to lose. It is a completely unacceptable risk to take.
I have been busy with the DMM and have tested some of the larger tantalum capacitors although my readings are not always consistent. However, due to the fact they soldered to the board and thus in circuit, I don't know if this is going to show me anything. As has been mentioned, I'd expect them to have properly blown up.
Haven't tested the MOSFETs with the DMM but the fact the motors are turning very slowly implies they are getting some power. Not 100% sure that's what they're for but there are 2 of them and 2 motors.
The speed controller works because in manual mode the laser head spins round at a normal speed. Unplugging it causes the motor to speed up. The unit has 2 speeds and they both work.
There are no obvious failures on the board(s) - no blown components or melty bits. Trying to reverse engineer the circuitry with my very limited knowledge is a fun learning experience.
I suspect the MOSFETs are not driving the motors, that's probably all in the speed controller. If the motors can spin both ways, that requires an H-bridge which would use 4 transistors per motor.
Do the FETs have inductors near them? They might be part of a switch mode power supply, either two different supplies or one synchronous supply.
The speed controller I speak of is for the laser head (there's a reluctor ring with a optical sensor). I will go and take some photos this morning.
The 8958A ICs have 2 MOSFETs in each - according to the datasheet
on pins 1,2,7,8 there is an N-type MOSFET. So pin 1 (source) should be connected to ground and to turn it on, a voltage needs to be applied to pin 2 (which will enable pins 7 and 8) - could I test by just shorting between 2 and 7 (or 8)?
Edit: yes that does work, although it turns out there are 2 8958A chips for each motor (one for each direction) and they only seem to use the N-type FET. Proves again nothing is wrong with the motors and if PhotoBucket wasn't so slow I'd be posting the pictures right now!
I've identified a couple more components. There are two 5201-33YM voltage regulators (below the 6V POWER in the photo above, just below the orange capacitor (106C)). The 16 pin IC to the left of the motor 1 8598A is a 78HC08D NAND gate.
Haven't actually tried any continuity tests on the MOSFETs yet, come to think of it, I've only confirmed that they do control the motors (you can see the traces on the circuit board going directly to the motor terminals)
2 pairs of MOSFETs for each motor is definitely an H-bridge. If you're confused about it not using P-channel FETs, whatever's driving the top half of the bridge is probably using a bootstrap driver.
Can you post full res images? It looks like photobucket killed the resolution so when I try to zoom in near the power connector is so pixellated I can't even tell how the diode near the connector is hooked up. I can't even see which end is the anode or cathode.
I think it'd be best to look at the power section near the conenctor, in particular the diode and voltage regulators.
Can try uploading differently tomorrow. The fact that one motor spins as it should (the laser head driver) tells me the main power regulator is probably fine so I'll be looking to test those 3.3V regulators, assuming they are the same. Difficult to read. Actually, my wife gave me a smartphone microscope that I could try...
It's better, but the flash bleaches out the side of the board of interest. Perhaps better backround lighting and turn off the flash, then some arrows with IC numbers.
Hi,
I find in 99% of ALL phone pictures of close objects, less than 50cm, the flash is more a hindrance than a help.
The resolution of your picture is excellent.
