Lasermad.com

Suggestions for improvements, mistakes, hints here please.

Hi Tony,
in the PCB assembly (page1) you wrote:
Now a modification before going any further. There's a track connecting the HV capactiros to the main HV rail here:

Image

It's under the resistor in the previous pictures but you can see where the PCB has been cut. Cut through this track as it's now connected to the HV supply by that resistor.

it seems that the location to cut the track is not correct: the image you showed is the Bottom Gerber seen from above: so left and right are inverted. The correct location (under the resistor and at the left of the 2x75V zeners) is here (see image in attached file)

It's the track that connects the HV capacitors to the x92 transistors, directly next to them.

So is the above diagram correct or NOT?

The track in the original instructions is different.

Maybe if this picture by Skyraider is CORRECT then it should REPLACE the pictures in the instructions.

Just a suggestion.

Firdaus

The resistor is to prevent the capacitors damaging the driver transistor if mechanical shock causes a momentary short in one of the tubes so should be fitted in series with them.

Hi Tony,
I've got as far as starting assembly of the relay 5-tube module and am having problems getting power to the levitating module. In the step where we need to measure across the 3v9 zener, I'm getting basically 0V. I have measured the coil at around 4.2 ohms, which I calculated as roughly correct, measuring the circumference of the coil, estimating the length and using 0.2mm diameter wire, so I'm confident the coil hasn't shorted anywhere.

I can float the magnet above the levitation base, so I'm assuming that the base is working correctly, unless the power transmission circuit is separate from the magnet driver circuit?

The kit only contained a strip of 2x 4.7nF capacitors (confirmed by measurement before soldering), rather than the three that are shown in the assembly instructions. I did try removing one and adding a 10nF cap that I had, to give ~14.7nF in case the tuning was that sensitive, but that made no perceptible difference.

Taken from the schematic posted by Skyraider (by the way, is the cathode connection of D18 incorrectly drawn? I have corrected to what I think it is in the image below) I have removed the crossed-out components to isolate the coil and tuning circuit from the rest of the circuit in case something was loading it, but still no luck.
I measured across the coil (in-circuit) with a scope, with the coil an inch or so above the magnets and am getting at most, perhaps 70mV of signal, mostly noise, but modulated on a triangle/sawtooth at around 67kHz (hard to lock the signal to get an accurate frequency measurement). What sort of signal amplitude should I be getting there?
I've measured the obvious stuff nearby with a multimeter to confirm components and connections, but with the black resist and lack of a component identification silk layer, the PCB is very difficult to trace, so I'm at a bit of a dead-end.

Do you have any ideas what the issue might be or any troubleshooting tips? I'm reasonably adept with electronics and have most necessary test equipment, but I'm not very experienced with magnetics and tuned circuits.

How critical is the 26 turns on the coil? As far as I know I counted 26, but would 25 or 27 prevent it from working? Unfortunately it is now glued, as per the instructions.

Thanks and kind regards,
Stu

Is the base coil getting warm? You should see 40-60Vp-p across the secondary so it looks like there's nothing driving it. What's the power being drawn by the base and is there any other sign of activity from the base LEDs?.

EDIT:
Please ignore this post - Turns out I am very stupid. After assembling the base, where it says to go on to the coil assembly, I jumped to the coil assembly for the clock module and missed the whole base coil assembly section.
I'll leave the rest of the post here in case anything else seems off though

The base draws about 90mA when idle, which goes up to around 1.9A when I float the magnet on top.
LD7 on the underside briefly illuminates green after power up before turning off again. I get nothing from the other LEDs underneath or from the 3mm LEDs LD5 and LD6 on the top.
The touch sensor circuit works and emits a tone which increases in pitch every second or so while I have my finger near it.
That sensor also goes walkabout sometimes when trying to float the magnet if it gets a bit too close. Then if I take the magnet away, it keeps increasing in pitch until I power cycle.

Cheers,
Stu